diff --git a/apps/server/execution/orchestrator.test.ts b/apps/server/execution/orchestrator.test.ts
index 6cf293d..3bbf1a1 100644
--- a/apps/server/execution/orchestrator.test.ts
+++ b/apps/server/execution/orchestrator.test.ts
@@ -46,6 +46,9 @@ function createMocks() {
     ensureBranch: vi.fn(),
     mergeBranch: vi.fn().mockResolvedValue({ success: true, message: 'merged', previousRef: 'abc000' }),
     diffBranches: vi.fn().mockResolvedValue(''),
+    diffBranchesStat: vi.fn().mockResolvedValue([]),
+    diffFileSingle: vi.fn().mockResolvedValue(''),
+    getHeadCommitHash: vi.fn().mockResolvedValue('deadbeef00000000000000000000000000000000'),
     deleteBranch: vi.fn(),
     branchExists: vi.fn().mockResolvedValue(true),
     remoteBranchExists: vi.fn().mockResolvedValue(false),
diff --git a/apps/server/execution/orchestrator.ts b/apps/server/execution/orchestrator.ts
index 5d29142..138aaa3 100644
--- a/apps/server/execution/orchestrator.ts
+++ b/apps/server/execution/orchestrator.ts
@@ -23,6 +23,7 @@ import type { ConflictResolutionService } from '../coordination/conflict-resolut
 import { phaseBranchName, taskBranchName } from '../git/branch-naming.js';
 import { ensureProjectClone } from '../git/project-clones.js';
 import { createModuleLogger } from '../logger/index.js';
+import { phaseMetaCache, fileDiffCache } from '../review/diff-cache.js';
 
 const log = createModuleLogger('execution-orchestrator');
 
@@ -253,6 +254,10 @@ export class ExecutionOrchestrator {
       log.info({ taskId, taskBranch, phaseBranch, project: project.name }, 'task branch merged into phase branch');
     }
 
+    // Invalidate diff cache — phase branch HEAD has advanced after merges
+    phaseMetaCache.invalidateByPrefix(`${phaseId}:`);
+    fileDiffCache.invalidateByPrefix(`${phaseId}:`);
+
     // Emit task:merged event
     const mergedEvent: TaskMergedEvent = {
       type: 'task:merged',
diff --git a/apps/server/git/branch-manager.ts b/apps/server/git/branch-manager.ts
index 9ba6d85..fd94ebb 100644
--- a/apps/server/git/branch-manager.ts
+++ b/apps/server/git/branch-manager.ts
@@ -6,7 +6,7 @@
  * a worktree to be checked out.
  */
 
-import type { MergeResult, MergeabilityResult, BranchCommit } from './types.js';
+import type { MergeResult, MergeabilityResult, BranchCommit, FileStatEntry } from './types.js';
 
 export interface BranchManager {
   /**
@@ -29,6 +29,27 @@ export interface BranchManager {
    */
   diffBranches(repoPath: string, baseBranch: string, headBranch: string): Promise<string>;
 
+  /**
+   * Get per-file metadata for changes between two branches.
+   * Uses three-dot diff (baseBranch...headBranch) — same divergence model as diffBranches.
+   * Binary files are included with status 'binary' and additions/deletions both 0.
+   * Does NOT return hunk content.
+   */
+  diffBranchesStat(repoPath: string, baseBranch: string, headBranch: string): Promise<FileStatEntry[]>;
+
+  /**
+   * Get the raw unified diff for a single file between two branches.
+   * Uses three-dot diff (baseBranch...headBranch).
+   * Returns empty string for binary files (caller must detect binary separately).
+   * filePath must be URL-decoded before being passed here.
+   */
+  diffFileSingle(repoPath: string, baseBranch: string, headBranch: string, filePath: string): Promise<string>;
+
+  /**
+   * Returns the current HEAD commit hash (40-char SHA) for the given branch in the repo.
+   */
+  getHeadCommitHash(repoPath: string, branch: string): Promise<string>;
+
   /**
    * Delete a branch. No-op if the branch doesn't exist.
    */
diff --git a/apps/server/git/simple-git-branch-manager.test.ts b/apps/server/git/simple-git-branch-manager.test.ts
index 18cb50a..f59c65b 100644
--- a/apps/server/git/simple-git-branch-manager.test.ts
+++ b/apps/server/git/simple-git-branch-manager.test.ts
@@ -65,6 +65,69 @@ async function createTestRepoWithRemote(): Promise<{
   };
 }
 
+/**
+ * Create a repo pair for testing diff operations.
+ * Sets up bare + clone with a 'feature' branch that has known changes vs 'main'.
+ */
+async function createTestRepoForDiff(): Promise<{
+  clonePath: string;
+  cleanup: () => Promise<void>;
+}> {
+  const tmpBase = await mkdtemp(path.join(tmpdir(), 'cw-diff-test-'));
+  const barePath = path.join(tmpBase, 'bare.git');
+  const workPath = path.join(tmpBase, 'work');
+  const clonePath = path.join(tmpBase, 'clone');
+
+  // Create bare repo
+  await simpleGit().init([barePath, '--bare']);
+
+  // Set up main branch in work dir
+  await simpleGit().clone(barePath, workPath);
+  const workGit = simpleGit(workPath);
+  await workGit.addConfig('user.email', 'test@example.com');
+  await workGit.addConfig('user.name', 'Test User');
+  await writeFile(path.join(workPath, 'README.md'), '# README\n');
+  await writeFile(path.join(workPath, 'to-delete.txt'), 'delete me\n');
+  await workGit.add(['README.md', 'to-delete.txt']);
+  await workGit.commit('Initial commit');
+  await workGit.push('origin', 'main');
+
+  // Clone and create feature branch with changes
+  await simpleGit().clone(barePath, clonePath);
+  const cloneGit = simpleGit(clonePath);
+  await cloneGit.addConfig('user.email', 'test@example.com');
+  await cloneGit.addConfig('user.name', 'Test User');
+  await cloneGit.checkoutLocalBranch('feature');
+
+  // Add new text file
+  await writeFile(path.join(clonePath, 'added.txt'), 'new content\n');
+  await cloneGit.add('added.txt');
+
+  // Modify existing file
+  await writeFile(path.join(clonePath, 'README.md'), '# README\n\nModified content\n');
+  await cloneGit.add('README.md');
+
+  // Delete a file
+  await cloneGit.rm(['to-delete.txt']);
+
+  // Add binary file
+  await writeFile(path.join(clonePath, 'image.bin'), Buffer.alloc(16));
+  await cloneGit.add('image.bin');
+
+  // Add file with space in name
+  await writeFile(path.join(clonePath, 'has space.txt'), 'content\n');
+  await cloneGit.add('has space.txt');
+
+  await cloneGit.commit('Feature branch changes');
+
+  return {
+    clonePath,
+    cleanup: async () => {
+      await rm(tmpBase, { recursive: true, force: true });
+    },
+  };
+}
+
 describe('SimpleGitBranchManager', () => {
   let clonePath: string;
   let cleanup: () => Promise<void>;
@@ -108,3 +171,80 @@ describe('SimpleGitBranchManager', () => {
     });
   });
 });
+
+describe('SimpleGitBranchManager - diffBranchesStat and diffFileSingle', () => {
+  let clonePath: string;
+  let cleanup: () => Promise<void>;
+  let branchManager: SimpleGitBranchManager;
+
+  beforeEach(async () => {
+    const setup = await createTestRepoForDiff();
+    clonePath = setup.clonePath;
+    cleanup = setup.cleanup;
+    branchManager = new SimpleGitBranchManager();
+  });
+
+  afterEach(async () => {
+    await cleanup();
+  });
+
+  describe('diffBranchesStat', () => {
+    it('returns correct entries for added, modified, and deleted text files', async () => {
+      const entries = await branchManager.diffBranchesStat(clonePath, 'main', 'feature');
+      const added = entries.find(e => e.path === 'added.txt');
+      const modified = entries.find(e => e.path === 'README.md');
+      const deleted = entries.find(e => e.path === 'to-delete.txt');
+
+      expect(added?.status).toBe('added');
+      expect(added?.additions).toBeGreaterThan(0);
+      expect(modified?.status).toBe('modified');
+      expect(deleted?.status).toBe('deleted');
+      expect(deleted?.deletions).toBeGreaterThan(0);
+    });
+
+    it('marks binary files as status=binary with additions=0, deletions=0', async () => {
+      const entries = await branchManager.diffBranchesStat(clonePath, 'main', 'feature');
+      const binary = entries.find(e => e.path === 'image.bin');
+      expect(binary?.status).toBe('binary');
+      expect(binary?.additions).toBe(0);
+      expect(binary?.deletions).toBe(0);
+    });
+
+    it('returns empty array when there are no changes', async () => {
+      const entries = await branchManager.diffBranchesStat(clonePath, 'main', 'main');
+      expect(entries).toEqual([]);
+    });
+
+    it('handles files with spaces in their names', async () => {
+      const entries = await branchManager.diffBranchesStat(clonePath, 'main', 'feature');
+      const spaced = entries.find(e => e.path === 'has space.txt');
+      expect(spaced).toBeDefined();
+      expect(spaced?.status).toBe('added');
+    });
+  });
+
+  describe('diffFileSingle', () => {
+    it('returns unified diff containing addition hunks for an added file', async () => {
+      const diff = await branchManager.diffFileSingle(clonePath, 'main', 'feature', 'added.txt');
+      expect(diff).toContain('+');
+      expect(diff).toContain('added.txt');
+    });
+
+    it('returns unified diff with removal hunks for a deleted file', async () => {
+      const diff = await branchManager.diffFileSingle(clonePath, 'main', 'feature', 'to-delete.txt');
+      expect(diff).toContain('-');
+      expect(diff).toContain('to-delete.txt');
+    });
+
+    it('returns string for a binary file', async () => {
+      const diff = await branchManager.diffFileSingle(clonePath, 'main', 'feature', 'image.bin');
+      // git diff returns empty or a "Binary files differ" line — no hunk content
+      expect(typeof diff).toBe('string');
+    });
+
+    it('handles file paths with spaces', async () => {
+      const diff = await branchManager.diffFileSingle(clonePath, 'main', 'feature', 'has space.txt');
+      expect(diff).toContain('has space.txt');
+    });
+  });
+});
diff --git a/apps/server/git/simple-git-branch-manager.ts b/apps/server/git/simple-git-branch-manager.ts
index 47b690e..bfe969d 100644
--- a/apps/server/git/simple-git-branch-manager.ts
+++ b/apps/server/git/simple-git-branch-manager.ts
@@ -11,11 +11,31 @@ import { mkdtempSync, rmSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { simpleGit } from 'simple-git';
 import type { BranchManager } from './branch-manager.js';
-import type { MergeResult, MergeabilityResult, BranchCommit } from './types.js';
+import type { MergeResult, MergeabilityResult, BranchCommit, FileStatEntry } from './types.js';
 import { createModuleLogger } from '../logger/index.js';
 
 const log = createModuleLogger('branch-manager');
 
+/**
+ * Normalize a numstat path to the new path for rename entries.
+ * Handles patterns like:
+ *   - "{old.txt => new.txt}" → "new.txt"
+ *   - "dir/{old.txt => new.txt}" → "dir/new.txt"
+ *   - "old_dir/file.txt => new_dir/file.txt" → "new_dir/file.txt"
+ */
+function normalizeNumstatPath(pathStr: string): string {
+  const braceMatch = pathStr.match(/^(.*)\{(.*) => (.*)\}(.*)$/);
+  if (braceMatch) {
+    const [, prefix, , newPart, suffix] = braceMatch;
+    return `${prefix}${newPart}${suffix}`;
+  }
+  const arrowMatch = pathStr.match(/^.* => (.+)$/);
+  if (arrowMatch) {
+    return arrowMatch[1];
+  }
+  return pathStr;
+}
+
 export class SimpleGitBranchManager implements BranchManager {
   async ensureBranch(repoPath: string, branch: string, baseBranch: string): Promise<void> {
     const git = simpleGit(repoPath);
@@ -97,6 +117,97 @@ export class SimpleGitBranchManager implements BranchManager {
     return diff;
   }
 
+  async diffBranchesStat(repoPath: string, baseBranch: string, headBranch: string): Promise<FileStatEntry[]> {
+    const git = simpleGit(repoPath);
+    const range = `${baseBranch}...${headBranch}`;
+
+    const [nameStatusRaw, numStatRaw] = await Promise.all([
+      git.raw(['diff', '--name-status', range]),
+      git.raw(['diff', '--numstat', range]),
+    ]);
+
+    if (!nameStatusRaw.trim()) return [];
+
+    // Parse numstat: "<additions>\t<deletions>\t<path>"
+    // Binary files: "-\t-\t<path>"
+    const numStatMap = new Map<string, { additions: number; deletions: number; binary: boolean }>();
+    for (const line of numStatRaw.split('\n')) {
+      if (!line.trim()) continue;
+      const tabIdx1 = line.indexOf('\t');
+      const tabIdx2 = line.indexOf('\t', tabIdx1 + 1);
+      if (tabIdx1 === -1 || tabIdx2 === -1) continue;
+      const addStr = line.slice(0, tabIdx1);
+      const delStr = line.slice(tabIdx1 + 1, tabIdx2);
+      const pathStr = line.slice(tabIdx2 + 1);
+      const binary = addStr === '-' && delStr === '-';
+      // Normalize rename paths like "{old => new}" or "dir/{old => new}/file" to new path
+      const newPath = normalizeNumstatPath(pathStr);
+      numStatMap.set(newPath, {
+        additions: binary ? 0 : parseInt(addStr, 10),
+        deletions: binary ? 0 : parseInt(delStr, 10),
+        binary,
+      });
+    }
+
+    // Parse name-status: "<status>\t<path>" or "<Rxx>\t<oldPath>\t<newPath>"
+    const entries: FileStatEntry[] = [];
+    for (const line of nameStatusRaw.split('\n')) {
+      if (!line.trim()) continue;
+      const parts = line.split('\t');
+      if (parts.length < 2) continue;
+
+      const statusCode = parts[0];
+      let status: FileStatEntry['status'];
+      let filePath: string;
+      let oldPath: string | undefined;
+
+      if (statusCode.startsWith('R')) {
+        status = 'renamed';
+        oldPath = parts[1];
+        filePath = parts[2];
+      } else if (statusCode === 'A') {
+        status = 'added';
+        filePath = parts[1];
+      } else if (statusCode === 'M') {
+        status = 'modified';
+        filePath = parts[1];
+      } else if (statusCode === 'D') {
+        status = 'deleted';
+        filePath = parts[1];
+      } else {
+        status = 'modified';
+        filePath = parts[1];
+      }
+
+      const numStat = numStatMap.get(filePath);
+      if (numStat?.binary) {
+        status = 'binary';
+      }
+
+      const entry: FileStatEntry = {
+        path: filePath,
+        status,
+        additions: numStat?.additions ?? 0,
+        deletions: numStat?.deletions ?? 0,
+      };
+      if (oldPath !== undefined) entry.oldPath = oldPath;
+      entries.push(entry);
+    }
+
+    return entries;
+  }
+
+  async diffFileSingle(repoPath: string, baseBranch: string, headBranch: string, filePath: string): Promise<string> {
+    const git = simpleGit(repoPath);
+    return git.diff([`${baseBranch}...${headBranch}`, '--', filePath]);
+  }
+
+  async getHeadCommitHash(repoPath: string, branch: string): Promise<string> {
+    const git = simpleGit(repoPath);
+    const result = await git.raw(['rev-parse', branch]);
+    return result.trim();
+  }
+
   async deleteBranch(repoPath: string, branch: string): Promise<void> {
     const git = simpleGit(repoPath);
     const exists = await this.branchExists(repoPath, branch);
diff --git a/apps/server/git/types.ts b/apps/server/git/types.ts
index 51a35b7..00cb829 100644
--- a/apps/server/git/types.ts
+++ b/apps/server/git/types.ts
@@ -100,6 +100,29 @@ export interface BranchCommit {
   deletions: number;
 }
 
+// =============================================================================
+// File Stat Entry (per-file diff metadata)
+// =============================================================================
+
+/**
+ * Metadata for a single file changed between two branches.
+ * No hunk content — only path, status, and line-count statistics.
+ */
+export interface FileStatEntry {
+  /** New path (or old path for deletions) */
+  path: string;
+  /** Only set for renames — the path before the rename */
+  oldPath?: string;
+  /** Nature of the change */
+  status: 'added' | 'modified' | 'deleted' | 'renamed' | 'binary';
+  /** Lines added (0 for binary files) */
+  additions: number;
+  /** Lines deleted (0 for binary files) */
+  deletions: number;
+  /** Which project clone this file belongs to (populated by callers in multi-project scenarios) */
+  projectId?: string;
+}
+
 // =============================================================================
 // WorktreeManager Port Interface
 // =============================================================================
diff --git a/apps/server/review/diff-cache.test.ts b/apps/server/review/diff-cache.test.ts
new file mode 100644
index 0000000..ddb1622
--- /dev/null
+++ b/apps/server/review/diff-cache.test.ts
@@ -0,0 +1,76 @@
+/**
+ * Unit tests for DiffCache class.
+ *
+ * Tests TTL expiry, prefix invalidation, and env-var TTL configuration.
+ */
+
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { DiffCache } from './diff-cache.js';
+
+afterEach(() => {
+  vi.restoreAllMocks();
+});
+
+describe('DiffCache', () => {
+  it('returns undefined for a key that was never set', () => {
+    const cache = new DiffCache<string>(5000);
+    expect(cache.get('nonexistent')).toBeUndefined();
+  });
+
+  it('returns value when entry has not expired', () => {
+    vi.spyOn(Date, 'now').mockReturnValue(1000);
+    const cache = new DiffCache<string>(5000);
+    cache.set('key', 'value');
+    vi.spyOn(Date, 'now').mockReturnValue(5999); // 4999ms elapsed, TTL=5000
+    expect(cache.get('key')).toBe('value');
+  });
+
+  it('returns undefined and deletes the entry when TTL has elapsed', () => {
+    vi.spyOn(Date, 'now').mockReturnValue(1000);
+    const cache = new DiffCache<string>(5000);
+    cache.set('key', 'value');
+    vi.spyOn(Date, 'now').mockReturnValue(6001); // 5001ms elapsed, TTL=5000
+    expect(cache.get('key')).toBeUndefined();
+    // Verify the key is no longer stored (second get also returns undefined)
+    vi.spyOn(Date, 'now').mockReturnValue(6001);
+    expect(cache.get('key')).toBeUndefined();
+  });
+
+  it('overwrites an existing entry and resets its TTL', () => {
+    vi.spyOn(Date, 'now').mockReturnValue(1000);
+    const cache = new DiffCache<string>(5000);
+    cache.set('key', 'first');
+    vi.spyOn(Date, 'now').mockReturnValue(4000); // overwrite before expiry
+    cache.set('key', 'second');
+    vi.spyOn(Date, 'now').mockReturnValue(8999); // 4999ms after overwrite, TTL=5000
+    expect(cache.get('key')).toBe('second');
+    vi.spyOn(Date, 'now').mockReturnValue(9001); // 5001ms after overwrite
+    expect(cache.get('key')).toBeUndefined();
+  });
+
+  it('invalidateByPrefix removes all matching keys and preserves others', () => {
+    const cache = new DiffCache<string>(60_000);
+    cache.set('phase-1:abc', 'a');
+    cache.set('phase-1:abc:file.ts', 'b');
+    cache.set('phase-2:xyz', 'c');
+    cache.invalidateByPrefix('phase-1:');
+    expect(cache.get('phase-1:abc')).toBeUndefined();
+    expect(cache.get('phase-1:abc:file.ts')).toBeUndefined();
+    expect(cache.get('phase-2:xyz')).toBe('c');
+  });
+
+  it('singleton instances use REVIEW_DIFF_CACHE_TTL_MS env var for TTL', async () => {
+    vi.resetModules();
+    vi.stubEnv('REVIEW_DIFF_CACHE_TTL_MS', '1000');
+    const { phaseMetaCache } = await import('./diff-cache.js');
+
+    vi.spyOn(Date, 'now').mockReturnValue(0);
+    phaseMetaCache.set('key', {} as any);
+    vi.spyOn(Date, 'now').mockReturnValue(999);
+    expect(phaseMetaCache.get('key')).toBeDefined();
+    vi.spyOn(Date, 'now').mockReturnValue(1001);
+    expect(phaseMetaCache.get('key')).toBeUndefined();
+
+    vi.unstubAllEnvs();
+  });
+});
diff --git a/apps/server/review/diff-cache.ts b/apps/server/review/diff-cache.ts
new file mode 100644
index 0000000..44cb1ec
--- /dev/null
+++ b/apps/server/review/diff-cache.ts
@@ -0,0 +1,70 @@
+/**
+ * DiffCache — in-memory TTL cache for git diff results.
+ *
+ * Keyed by `phaseId:headHash` (or `phaseId:headHash:filePath` for per-file diffs).
+ * TTL defaults to 5 minutes, configurable via REVIEW_DIFF_CACHE_TTL_MS env var.
+ * Prefix-based invalidation clears all entries for a phase when a new commit lands.
+ */
+
+import type { FileStatEntry } from '../git/types.js';
+
+interface CacheEntry<T> {
+  value: T;
+  expiresAt: number;
+}
+
+export class DiffCache<T> {
+  private store = new Map<string, CacheEntry<T>>();
+  private ttlMs: number;
+
+  constructor(ttlMs: number) {
+    this.ttlMs = ttlMs;
+  }
+
+  get(key: string): T | undefined {
+    const entry = this.store.get(key);
+    if (!entry) return undefined;
+    if (Date.now() > entry.expiresAt) {
+      this.store.delete(key);
+      return undefined;
+    }
+    return entry.value;
+  }
+
+  set(key: string, value: T): void {
+    this.store.set(key, { value, expiresAt: Date.now() + this.ttlMs });
+  }
+
+  invalidateByPrefix(prefix: string): void {
+    for (const key of this.store.keys()) {
+      if (key.startsWith(prefix)) this.store.delete(key);
+    }
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Response shapes (mirror the return types of getPhaseReviewDiff / getFileDiff)
+// ---------------------------------------------------------------------------
+
+export interface PhaseMetaResponse {
+  phaseName: string;
+  sourceBranch: string;
+  targetBranch: string;
+  files: FileStatEntry[];
+  totalAdditions: number;
+  totalDeletions: number;
+}
+
+export interface FileDiffResponse {
+  binary: boolean;
+  rawDiff: string;
+}
+
+// ---------------------------------------------------------------------------
+// Singleton instances — TTL is read once at module load time
+// ---------------------------------------------------------------------------
+
+const TTL = parseInt(process.env.REVIEW_DIFF_CACHE_TTL_MS ?? '300000', 10);
+
+export const phaseMetaCache = new DiffCache<PhaseMetaResponse>(TTL);
+export const fileDiffCache = new DiffCache<FileDiffResponse>(TTL);
diff --git a/apps/server/test/integration/phase-review-diff.test.ts b/apps/server/test/integration/phase-review-diff.test.ts
new file mode 100644
index 0000000..036e12d
--- /dev/null
+++ b/apps/server/test/integration/phase-review-diff.test.ts
@@ -0,0 +1,256 @@
+/**
+ * Integration tests for getPhaseReviewDiff and getFileDiff tRPC procedures.
+ *
+ * Uses real git repos on disk (no cassettes) + an in-memory SQLite database.
+ * No network calls — purely local git operations.
+ */
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { mkdtemp, rm, writeFile, mkdir } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import { simpleGit } from 'simple-git';
+import { router, publicProcedure, createCallerFactory } from '../../trpc/trpc.js';
+import { phaseProcedures } from '../../trpc/routers/phase.js';
+import { createTestDatabase } from '../../db/repositories/drizzle/test-helpers.js';
+import {
+  DrizzleInitiativeRepository,
+  DrizzlePhaseRepository,
+  DrizzleProjectRepository,
+} from '../../db/repositories/drizzle/index.js';
+import { SimpleGitBranchManager } from '../../git/simple-git-branch-manager.js';
+import { getProjectCloneDir } from '../../git/project-clones.js';
+import type { TRPCContext } from '../../trpc/context.js';
+
+// ============================================================================
+// Test router & caller factory
+// ============================================================================
+
+const testRouter = router({
+  ...phaseProcedures(publicProcedure),
+});
+
+const createCaller = createCallerFactory(testRouter);
+
+// ============================================================================
+// Shared test state (set up once for the whole suite)
+// ============================================================================
+
+let workspaceRoot: string;
+let cleanup: () => Promise<void>;
+let phaseId: string;
+let pendingPhaseId: string;
+
+/**
+ * Build the test git repo with the required branches and files.
+ *
+ * Repo layout on the phase branch vs main:
+ *   file1.txt through file5.txt — added (10–20 lines each)
+ *   photo.bin                  — binary file (Buffer.alloc(32))
+ *   gone.txt                   — deleted (existed on main)
+ *   has space.txt              — added (contains text)
+ */
+async function setupGitRepo(clonePath: string): Promise<void> {
+  await mkdir(clonePath, { recursive: true });
+
+  const git = simpleGit(clonePath);
+  await git.init();
+  await git.addConfig('user.email', 'test@example.com');
+  await git.addConfig('user.name', 'Test');
+
+  // Commit gone.txt on main so it can be deleted on the phase branch
+  await writeFile(path.join(clonePath, 'gone.txt'), Array.from({ length: 5 }, (_, i) => `line ${i + 1}`).join('\n') + '\n');
+  await git.add('gone.txt');
+  await git.commit('Initial commit on main');
+
+  // Create phase branch from main
+  // phaseBranchName('main', 'test-phase') => 'main-phase-test-phase'
+  await git.checkoutLocalBranch('main-phase-test-phase');
+
+  // Add 5 text files
+  for (let i = 1; i <= 5; i++) {
+    const lines = Array.from({ length: 15 }, (_, j) => `Line ${j + 1} in file${i}`).join('\n') + '\n';
+    await writeFile(path.join(clonePath, `file${i}.txt`), lines);
+  }
+  await git.add(['file1.txt', 'file2.txt', 'file3.txt', 'file4.txt', 'file5.txt']);
+
+  // Add binary file
+  await writeFile(path.join(clonePath, 'photo.bin'), Buffer.alloc(32));
+  await git.add('photo.bin');
+
+  // Delete gone.txt
+  await git.rm(['gone.txt']);
+
+  // Add file with space in name
+  await writeFile(path.join(clonePath, 'has space.txt'), 'content with spaces\n');
+  await git.add('has space.txt');
+
+  await git.commit('Phase branch changes');
+}
+
+beforeAll(async () => {
+  // Create workspace root temp dir
+  workspaceRoot = await mkdtemp(path.join(tmpdir(), 'cw-phase-diff-test-'));
+  cleanup = async () => {
+    await rm(workspaceRoot, { recursive: true, force: true });
+  };
+
+  // Set up in-memory database
+  const db = createTestDatabase();
+  const initiativeRepo = new DrizzleInitiativeRepository(db);
+  const phaseRepo = new DrizzlePhaseRepository(db);
+  const projectRepo = new DrizzleProjectRepository(db);
+
+  // Create initiative with branch='main'
+  const initiative = await initiativeRepo.create({
+    name: 'Test Initiative',
+    branch: 'main',
+  });
+
+  // Create project — we'll set up the git repo at the expected clone path
+  const project = await projectRepo.create({
+    name: 'test-repo',
+    url: 'file:///dev/null', // won't be cloned — we create the repo directly
+    defaultBranch: 'main',
+  });
+
+  // Link project to initiative
+  await projectRepo.addProjectToInitiative(initiative.id, project.id);
+
+  // Set up git repo at the expected clone path
+  const relPath = getProjectCloneDir(project.name, project.id);
+  const clonePath = path.join(workspaceRoot, relPath);
+  await setupGitRepo(clonePath);
+
+  // Create reviewable phase (pending_review)
+  const phase = await phaseRepo.create({
+    initiativeId: initiative.id,
+    name: 'test-phase',
+    status: 'pending_review',
+  });
+  phaseId = phase.id;
+
+  // Create a non-reviewable phase (pending) for error test
+  const pendingPhase = await phaseRepo.create({
+    initiativeId: initiative.id,
+    name: 'pending-phase',
+    status: 'pending',
+  });
+  pendingPhaseId = pendingPhase.id;
+
+  // Store db and repos so the caller can use them
+  // (stored in module-level vars to be accessed in test helper)
+  Object.assign(sharedCtx, {
+    initiativeRepository: initiativeRepo,
+    phaseRepository: phaseRepo,
+    projectRepository: projectRepo,
+    branchManager: new SimpleGitBranchManager(),
+    workspaceRoot,
+  });
+});
+
+afterAll(async () => {
+  await cleanup?.();
+});
+
+// ============================================================================
+// Shared context (filled in beforeAll)
+// ============================================================================
+
+const sharedCtx: Partial<TRPCContext> = {
+  eventBus: { emit: () => {}, on: () => {}, off: () => {}, once: () => {} } as any,
+  serverStartedAt: null,
+  processCount: 0,
+};
+
+function getCaller() {
+  return createCaller(sharedCtx as TRPCContext);
+}
+
+// ============================================================================
+// Tests: getPhaseReviewDiff
+// ============================================================================
+
+describe('getPhaseReviewDiff', () => {
+  it('returns files array with correct metadata and no rawDiff field', async () => {
+    const start = Date.now();
+    const result = await getCaller().getPhaseReviewDiff({ phaseId });
+    const elapsed = Date.now() - start;
+
+    expect(result).not.toHaveProperty('rawDiff');
+    expect(result.files).toBeInstanceOf(Array);
+    // 5 text + 1 binary + 1 deleted + 1 spaced = 8 files
+    expect(result.files.length).toBeGreaterThanOrEqual(7);
+    expect(elapsed).toBeLessThan(3000);
+  });
+
+  it('includes binary file with status=binary, additions=0, deletions=0', async () => {
+    const result = await getCaller().getPhaseReviewDiff({ phaseId });
+    const bin = result.files.find((f) => f.path === 'photo.bin');
+    expect(bin?.status).toBe('binary');
+    expect(bin?.additions).toBe(0);
+    expect(bin?.deletions).toBe(0);
+  });
+
+  it('includes deleted file with status=deleted and nonzero deletions', async () => {
+    const result = await getCaller().getPhaseReviewDiff({ phaseId });
+    const del = result.files.find((f) => f.path === 'gone.txt');
+    expect(del?.status).toBe('deleted');
+    expect(del?.deletions).toBeGreaterThan(0);
+  });
+
+  it('computes totalAdditions and totalDeletions as sums over files', async () => {
+    const result = await getCaller().getPhaseReviewDiff({ phaseId });
+    const sumAdd = result.files.reduce((s, f) => s + f.additions, 0);
+    const sumDel = result.files.reduce((s, f) => s + f.deletions, 0);
+    expect(result.totalAdditions).toBe(sumAdd);
+    expect(result.totalDeletions).toBe(sumDel);
+  });
+
+  it('throws NOT_FOUND for unknown phaseId', async () => {
+    const err = await getCaller().getPhaseReviewDiff({ phaseId: 'nonexistent' }).catch((e) => e);
+    expect(err.code).toBe('NOT_FOUND');
+  });
+
+  it('throws BAD_REQUEST for phase not in reviewable status', async () => {
+    const err = await getCaller().getPhaseReviewDiff({ phaseId: pendingPhaseId }).catch((e) => e);
+    expect(err.code).toBe('BAD_REQUEST');
+  });
+});
+
+// ============================================================================
+// Tests: getFileDiff
+// ============================================================================
+
+describe('getFileDiff', () => {
+  it('returns rawDiff with unified diff for a normal file, under 1 second', async () => {
+    const start = Date.now();
+    const result = await getCaller().getFileDiff({ phaseId, filePath: 'file1.txt' });
+    const elapsed = Date.now() - start;
+
+    expect(result.binary).toBe(false);
+    expect(result.rawDiff).toContain('+');
+    expect(elapsed).toBeLessThan(1000);
+  });
+
+  it('returns binary=true and rawDiff="" for binary file', async () => {
+    const result = await getCaller().getFileDiff({ phaseId, filePath: 'photo.bin' });
+    expect(result.binary).toBe(true);
+    expect(result.rawDiff).toBe('');
+  });
+
+  it('returns removal hunks for a deleted file', async () => {
+    const result = await getCaller().getFileDiff({ phaseId, filePath: 'gone.txt' });
+    expect(result.binary).toBe(false);
+    expect(result.rawDiff).toContain('-');
+  });
+
+  it('handles URL-encoded file path with space', async () => {
+    const result = await getCaller().getFileDiff({
+      phaseId,
+      filePath: encodeURIComponent('has space.txt'),
+    });
+    expect(result.binary).toBe(false);
+    expect(result.rawDiff).toContain('has space.txt');
+  });
+});
diff --git a/apps/server/trpc/routers/phase.test.ts b/apps/server/trpc/routers/phase.test.ts
new file mode 100644
index 0000000..ec021bd
--- /dev/null
+++ b/apps/server/trpc/routers/phase.test.ts
@@ -0,0 +1,249 @@
+/**
+ * Integration tests for getPhaseReviewDiff caching behaviour.
+ *
+ * Verifies that git diff is only invoked once per HEAD hash and that
+ * cache invalidation after a task merge triggers a re-run.
+ */
+
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+import { router, publicProcedure, createCallerFactory } from '../trpc.js';
+import { phaseProcedures } from './phase.js';
+import type { TRPCContext } from '../context.js';
+import type { BranchManager } from '../../git/branch-manager.js';
+import { createTestDatabase } from '../../db/repositories/drizzle/test-helpers.js';
+import {
+  DrizzleInitiativeRepository,
+  DrizzlePhaseRepository,
+  DrizzleProjectRepository,
+} from '../../db/repositories/drizzle/index.js';
+import { phaseMetaCache, fileDiffCache } from '../../review/diff-cache.js';
+
+// =============================================================================
+// Mock ensureProjectClone — prevents actual git cloning
+// =============================================================================
+
+vi.mock('../../git/project-clones.js', () => ({
+  ensureProjectClone: vi.fn().mockResolvedValue('/fake/clone/path'),
+  getProjectCloneDir: vi.fn().mockReturnValue('repos/fake-project-id'),
+}));
+
+// =============================================================================
+// Test router
+// =============================================================================
+
+const testRouter = router({
+  ...phaseProcedures(publicProcedure),
+});
+
+const createCaller = createCallerFactory(testRouter);
+
+// =============================================================================
+// MockBranchManager
+// =============================================================================
+
+function makeMockBranchManager(): BranchManager {
+  return {
+    ensureBranch: vi.fn().mockResolvedValue(undefined),
+    mergeBranch: vi.fn().mockResolvedValue({ success: true, conflictFiles: [] }),
+    diffBranches: vi.fn().mockResolvedValue('diff --git a/file.ts'),
+    diffBranchesStat: vi.fn().mockResolvedValue([]),
+    diffFileSingle: vi.fn().mockResolvedValue('diff --git a/file.ts'),
+    deleteBranch: vi.fn().mockResolvedValue(undefined),
+    branchExists: vi.fn().mockResolvedValue(true),
+    remoteBranchExists: vi.fn().mockResolvedValue(true),
+    listCommits: vi.fn().mockResolvedValue([]),
+    diffCommit: vi.fn().mockResolvedValue(''),
+    getMergeBase: vi.fn().mockResolvedValue('mergebase123'),
+    pushBranch: vi.fn().mockResolvedValue(undefined),
+    checkMergeability: vi.fn().mockResolvedValue({ canMerge: true, conflicts: [] }),
+    fetchRemote: vi.fn().mockResolvedValue(undefined),
+    fastForwardBranch: vi.fn().mockResolvedValue(undefined),
+    updateRef: vi.fn().mockResolvedValue(undefined),
+    getHeadCommitHash: vi.fn().mockResolvedValue('abc123def456'),
+  };
+}
+
+// =============================================================================
+// Helpers
+// =============================================================================
+
+function createMockEventBus(): TRPCContext['eventBus'] {
+  return {
+    emit: vi.fn(),
+    on: vi.fn(),
+    off: vi.fn(),
+    once: vi.fn(),
+  };
+}
+
+interface SeedResult {
+  phaseId: string;
+  initiativeId: string;
+  projectId: string;
+}
+
+async function seedDatabase(): Promise<{
+  repos: {
+    initiativeRepo: DrizzleInitiativeRepository;
+    phaseRepo: DrizzlePhaseRepository;
+    projectRepo: DrizzleProjectRepository;
+  };
+  data: SeedResult;
+}> {
+  const db = createTestDatabase();
+  const initiativeRepo = new DrizzleInitiativeRepository(db);
+  const phaseRepo = new DrizzlePhaseRepository(db);
+  const projectRepo = new DrizzleProjectRepository(db);
+
+  const initiative = await initiativeRepo.create({
+    name: 'Test Initiative',
+    status: 'active',
+    branch: 'main',
+  });
+
+  const phase = await phaseRepo.create({
+    initiativeId: initiative.id,
+    name: 'Test Phase',
+    status: 'pending_review',
+  });
+
+  const project = await projectRepo.create({
+    name: 'Test Project',
+    url: 'https://github.com/test/repo',
+  });
+
+  await projectRepo.addProjectToInitiative(initiative.id, project.id);
+
+  return {
+    repos: { initiativeRepo, phaseRepo, projectRepo },
+    data: { phaseId: phase.id, initiativeId: initiative.id, projectId: project.id },
+  };
+}
+
+async function seedDatabaseNoProjects(): Promise<{
+  repos: {
+    initiativeRepo: DrizzleInitiativeRepository;
+    phaseRepo: DrizzlePhaseRepository;
+    projectRepo: DrizzleProjectRepository;
+  };
+  data: { phaseId: string };
+}> {
+  const db = createTestDatabase();
+  const initiativeRepo = new DrizzleInitiativeRepository(db);
+  const phaseRepo = new DrizzlePhaseRepository(db);
+  const projectRepo = new DrizzleProjectRepository(db);
+
+  const initiative = await initiativeRepo.create({
+    name: 'Test Initiative No Projects',
+    status: 'active',
+    branch: 'main',
+  });
+
+  const phase = await phaseRepo.create({
+    initiativeId: initiative.id,
+    name: 'Empty Phase',
+    status: 'pending_review',
+  });
+
+  return {
+    repos: { initiativeRepo, phaseRepo, projectRepo },
+    data: { phaseId: phase.id },
+  };
+}
+
+function makeCaller(
+  branchManager: BranchManager,
+  repos: {
+    initiativeRepo: DrizzleInitiativeRepository;
+    phaseRepo: DrizzlePhaseRepository;
+    projectRepo: DrizzleProjectRepository;
+  },
+) {
+  const ctx: TRPCContext = {
+    eventBus: createMockEventBus(),
+    serverStartedAt: null,
+    processCount: 0,
+    branchManager,
+    initiativeRepository: repos.initiativeRepo,
+    phaseRepository: repos.phaseRepo,
+    projectRepository: repos.projectRepo,
+    workspaceRoot: '/fake/workspace',
+  };
+  return createCaller(ctx);
+}
+
+// =============================================================================
+// Tests
+// =============================================================================
+
+beforeEach(() => {
+  // Clear caches between tests to ensure isolation
+  phaseMetaCache.invalidateByPrefix('');
+  fileDiffCache.invalidateByPrefix('');
+});
+
+describe('getPhaseReviewDiff caching', () => {
+  it('second call for same phase/HEAD returns cached result without calling git again', async () => {
+    const { repos, data } = await seedDatabase();
+    const branchManager = makeMockBranchManager();
+    const diffBranchesSpy = vi.spyOn(branchManager, 'diffBranchesStat');
+    const caller = makeCaller(branchManager, repos);
+
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+
+    expect(diffBranchesSpy).toHaveBeenCalledTimes(1);
+  });
+
+  it('after cache invalidation, next call re-runs git diff', async () => {
+    const { repos, data } = await seedDatabase();
+    const branchManager = makeMockBranchManager();
+    const diffBranchesSpy = vi.spyOn(branchManager, 'diffBranchesStat');
+    const caller = makeCaller(branchManager, repos);
+
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+    expect(diffBranchesSpy).toHaveBeenCalledTimes(1);
+
+    // Simulate a task merge → cache invalidated
+    phaseMetaCache.invalidateByPrefix(`${data.phaseId}:`);
+
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+    expect(diffBranchesSpy).toHaveBeenCalledTimes(2);
+  });
+
+  it('different HEAD hashes for same phase are treated as distinct cache entries', async () => {
+    const { repos, data } = await seedDatabase();
+    const branchManager = makeMockBranchManager();
+    const diffBranchesSpy = vi.spyOn(branchManager, 'diffBranchesStat');
+    const caller = makeCaller(branchManager, repos);
+
+    // First call with headHash = 'abc123'
+    vi.spyOn(branchManager, 'getHeadCommitHash').mockResolvedValueOnce('abc123');
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+
+    // Second call with headHash = 'def456' (simulates a new commit)
+    vi.spyOn(branchManager, 'getHeadCommitHash').mockResolvedValueOnce('def456');
+    await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+
+    expect(diffBranchesSpy).toHaveBeenCalledTimes(2);
+  });
+
+  it('throws NOT_FOUND for nonexistent phaseId', async () => {
+    const { repos } = await seedDatabase();
+    const caller = makeCaller(makeMockBranchManager(), repos);
+
+    await expect(caller.getPhaseReviewDiff({ phaseId: 'nonexistent' }))
+      .rejects.toMatchObject({ code: 'NOT_FOUND' });
+  });
+
+  it('phase with no projects returns empty result without calling git', async () => {
+    const { repos, data } = await seedDatabaseNoProjects();
+    const branchManager = makeMockBranchManager();
+    const diffBranchesSpy = vi.spyOn(branchManager, 'diffBranchesStat');
+    const caller = makeCaller(branchManager, repos);
+
+    const result = await caller.getPhaseReviewDiff({ phaseId: data.phaseId });
+    expect(diffBranchesSpy).not.toHaveBeenCalled();
+    expect(result).toHaveProperty('phaseName');
+  });
+});
diff --git a/apps/server/trpc/routers/phase.ts b/apps/server/trpc/routers/phase.ts
index be59ef2..9381722 100644
--- a/apps/server/trpc/routers/phase.ts
+++ b/apps/server/trpc/routers/phase.ts
@@ -4,11 +4,14 @@
 
 import { TRPCError } from '@trpc/server';
 import { z } from 'zod';
+import { simpleGit } from 'simple-git';
 import type { Phase } from '../../db/schema.js';
 import type { ProcedureBuilder } from '../trpc.js';
 import { requirePhaseRepository, requireTaskRepository, requireBranchManager, requireInitiativeRepository, requireProjectRepository, requireExecutionOrchestrator, requireReviewCommentRepository, requireChangeSetRepository } from './_helpers.js';
 import { phaseBranchName } from '../../git/branch-naming.js';
 import { ensureProjectClone } from '../../git/project-clones.js';
+import type { FileStatEntry } from '../../git/types.js';
+import { phaseMetaCache, fileDiffCache } from '../../review/diff-cache.js';
 
 export function phaseProcedures(publicProcedure: ProcedureBuilder) {
   return {
@@ -230,26 +233,124 @@ export function phaseProcedures(publicProcedure: ProcedureBuilder) {
 
         const initBranch = initiative.branch;
         const phBranch = phaseBranchName(initBranch, phase.name);
-        // For completed phases, use stored merge base; for pending_review, use initiative branch
         const diffBase = (phase.status === 'completed' && phase.mergeBase) ? phase.mergeBase : initBranch;
 
         const projects = await projectRepo.findProjectsByInitiativeId(phase.initiativeId);
-        let rawDiff = '';
+
+        if (projects.length === 0) {
+          return {
+            phaseName: phase.name,
+            sourceBranch: phBranch,
+            targetBranch: initBranch,
+            files: [],
+            totalAdditions: 0,
+            totalDeletions: 0,
+          };
+        }
+
+        const firstClone = await ensureProjectClone(projects[0], ctx.workspaceRoot!);
+        const headHash = await branchManager.getHeadCommitHash(firstClone, phBranch);
+        const cacheKey = `${input.phaseId}:${headHash}`;
+
+        type PhaseReviewDiffResult = { phaseName: string; sourceBranch: string; targetBranch: string; files: FileStatEntry[]; totalAdditions: number; totalDeletions: number };
+        const cached = phaseMetaCache.get(cacheKey) as PhaseReviewDiffResult | undefined;
+        if (cached) return cached;
+
+        const files: FileStatEntry[] = [];
 
         for (const project of projects) {
           const clonePath = await ensureProjectClone(project, ctx.workspaceRoot!);
-          const diff = await branchManager.diffBranches(clonePath, diffBase, phBranch);
-          if (diff) {
-            rawDiff += diff + '\n';
+          const entries = await branchManager.diffBranchesStat(clonePath, diffBase, phBranch);
+          for (const entry of entries) {
+            const tagged: FileStatEntry = { ...entry, projectId: project.id };
+            if (projects.length > 1) {
+              tagged.path = `${project.name}/${entry.path}`;
+              if (entry.oldPath) {
+                tagged.oldPath = `${project.name}/${entry.oldPath}`;
+              }
+            }
+            files.push(tagged);
           }
         }
 
-        return {
+        const totalAdditions = files.reduce((sum, f) => sum + f.additions, 0);
+        const totalDeletions = files.reduce((sum, f) => sum + f.deletions, 0);
+
+        const result = {
           phaseName: phase.name,
           sourceBranch: phBranch,
           targetBranch: initBranch,
-          rawDiff,
+          files,
+          totalAdditions,
+          totalDeletions,
         };
+        phaseMetaCache.set(cacheKey, result);
+        return result;
+      }),
+
+    getFileDiff: publicProcedure
+      .input(z.object({
+        phaseId: z.string().min(1),
+        filePath: z.string().min(1),
+        projectId: z.string().optional(),
+      }))
+      .query(async ({ ctx, input }) => {
+        const phaseRepo = requirePhaseRepository(ctx);
+        const initiativeRepo = requireInitiativeRepository(ctx);
+        const projectRepo = requireProjectRepository(ctx);
+        const branchManager = requireBranchManager(ctx);
+
+        const phase = await phaseRepo.findById(input.phaseId);
+        if (!phase) {
+          throw new TRPCError({ code: 'NOT_FOUND', message: `Phase '${input.phaseId}' not found` });
+        }
+        if (phase.status !== 'pending_review' && phase.status !== 'completed') {
+          throw new TRPCError({ code: 'BAD_REQUEST', message: `Phase is not reviewable (status: ${phase.status})` });
+        }
+
+        const initiative = await initiativeRepo.findById(phase.initiativeId);
+        if (!initiative?.branch) {
+          throw new TRPCError({ code: 'BAD_REQUEST', message: 'Initiative has no branch configured' });
+        }
+
+        const initBranch = initiative.branch;
+        const phBranch = phaseBranchName(initBranch, phase.name);
+        const diffBase = (phase.status === 'completed' && phase.mergeBase) ? phase.mergeBase : initBranch;
+
+        const decodedPath = decodeURIComponent(input.filePath);
+
+        const projects = await projectRepo.findProjectsByInitiativeId(phase.initiativeId);
+
+        const firstClone = await ensureProjectClone(projects[0], ctx.workspaceRoot!);
+        const headHash = await branchManager.getHeadCommitHash(firstClone, phBranch);
+        const cacheKey = `${input.phaseId}:${headHash}:${input.filePath}`;
+        const cached = fileDiffCache.get(cacheKey);
+        if (cached) return cached;
+
+        let clonePath: string;
+        if (input.projectId) {
+          const project = projects.find((p) => p.id === input.projectId);
+          if (!project) {
+            throw new TRPCError({ code: 'NOT_FOUND', message: `Project '${input.projectId}' not found for this phase` });
+          }
+          clonePath = await ensureProjectClone(project, ctx.workspaceRoot!);
+        } else {
+          clonePath = firstClone;
+        }
+
+        const git = simpleGit(clonePath);
+        // Binary files appear as "-\t-\t<path>" in --numstat output
+        const numstatOut = await git.raw(['diff', '--numstat', `${diffBase}...${phBranch}`, '--', decodedPath]);
+        if (numstatOut.trim() && numstatOut.startsWith('-\t-\t')) {
+          const binaryResult = { binary: true, rawDiff: '' };
+          fileDiffCache.set(cacheKey, binaryResult);
+          return binaryResult;
+        }
+
+        const rawDiff = await branchManager.diffFileSingle(clonePath, diffBase, phBranch, decodedPath);
+        const result = { binary: false, rawDiff };
+        fileDiffCache.set(cacheKey, result);
+        return result;
       }),
 
     approvePhaseReview: publicProcedure
diff --git a/apps/web/package.json b/apps/web/package.json
index bae73ef..d0caa00 100644
--- a/apps/web/package.json
+++ b/apps/web/package.json
@@ -27,12 +27,14 @@
     "@tiptap/suggestion": "^3.19.0",
     "@trpc/client": "^11.9.0",
     "@trpc/react-query": "^11.9.0",
+    "@types/react-window": "^1.8.8",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "geist": "^1.7.0",
     "lucide-react": "^0.563.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
+    "react-window": "^2.2.7",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.4.0",
     "tippy.js": "^6.3.7"
diff --git a/apps/web/src/components/review/ConflictResolutionPanel.tsx b/apps/web/src/components/review/ConflictResolutionPanel.tsx
index ea2ff36..95dc750 100644
--- a/apps/web/src/components/review/ConflictResolutionPanel.tsx
+++ b/apps/web/src/components/review/ConflictResolutionPanel.tsx
@@ -11,7 +11,7 @@ interface ConflictResolutionPanelProps {
 }
 
 export function ConflictResolutionPanel({ initiativeId, conflicts, onResolved }: ConflictResolutionPanelProps) {
-  const { state, agent, questions, spawn, resume, stop, dismiss } = useConflictAgent(initiativeId);
+  const { state, agent: _agent, questions, spawn, resume, stop, dismiss } = useConflictAgent(initiativeId);
   const [showManual, setShowManual] = useState(false);
   const prevStateRef = useRef<string | null>(null);
 
diff --git a/apps/web/src/components/review/DiffViewer.test.tsx b/apps/web/src/components/review/DiffViewer.test.tsx
new file mode 100644
index 0000000..062de65
--- /dev/null
+++ b/apps/web/src/components/review/DiffViewer.test.tsx
@@ -0,0 +1,192 @@
+// @vitest-environment happy-dom
+import "@testing-library/jest-dom/vitest";
+import { render, screen, act } from "@testing-library/react";
+import { vi, describe, it, expect, beforeEach, afterEach } from "vitest";
+import { DiffViewer } from "./DiffViewer";
+import type { FileDiff } from "./types";
+
+// ── Module mocks ──────────────────────────────────────────────────────────────
+
+vi.mock("./FileCard", () => ({
+  FileCard: ({ file }: { file: FileDiff }) => (
+    <div data-testid="file-card" data-path={file.newPath} />
+  ),
+}));
+
+// Hoist the fetch mock so it can be referenced inside vi.mock factories
+const { mockGetFileDiffFetch } = vi.hoisted(() => ({
+  mockGetFileDiffFetch: vi.fn().mockResolvedValue({ rawDiff: "" }),
+}));
+
+vi.mock("@/lib/trpc", () => ({
+  trpc: {
+    useUtils: () => ({
+      getFileDiff: { fetch: mockGetFileDiffFetch },
+    }),
+  },
+}));
+
+// DiffViewer calls useQueryClient() (even though the return value is unused).
+// Provide a minimal mock so the hook doesn't throw outside a QueryClientProvider.
+vi.mock("@tanstack/react-query", async (importOriginal) => {
+  const actual =
+    await importOriginal<typeof import("@tanstack/react-query")>();
+  return { ...actual, useQueryClient: () => ({}) };
+});
+
+// ── IntersectionObserver mock ─────────────────────────────────────────────────
+
+let observerCallback: IntersectionObserverCallback | null = null;
+const observedElements = new Set<Element>();
+
+// Class (not arrow function) so it can be used with `new IntersectionObserver(...)`
+class MockIntersectionObserver {
+  constructor(cb: IntersectionObserverCallback) {
+    observerCallback = cb;
+  }
+  observe(el: Element) {
+    observedElements.add(el);
+  }
+  unobserve(el: Element) {
+    observedElements.delete(el);
+  }
+  disconnect() {
+    observedElements.clear();
+  }
+}
+
+beforeEach(() => {
+  vi.stubGlobal("IntersectionObserver", MockIntersectionObserver);
+  observedElements.clear();
+  observerCallback = null;
+  mockGetFileDiffFetch.mockClear();
+  mockGetFileDiffFetch.mockResolvedValue({ rawDiff: "" });
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+/**
+ * Fire the IntersectionObserver callback with a set of intersecting and
+ * non-intersecting file paths. The target element is simulated by an object
+ * whose dataset.filePath matches the DiffViewer's data-file-path attribute.
+ */
+function fireIntersection(
+  intersectingPaths: string[],
+  nonIntersectingPaths: string[] = [],
+) {
+  if (!observerCallback) return;
+  const entries = [
+    ...intersectingPaths.map((p) => ({
+      isIntersecting: true,
+      target: { dataset: { filePath: p } } as unknown as Element,
+    })),
+    ...nonIntersectingPaths.map((p) => ({
+      isIntersecting: false,
+      target: { dataset: { filePath: p } } as unknown as Element,
+    })),
+  ] as IntersectionObserverEntry[];
+  act(() => {
+    observerCallback!(entries, {} as IntersectionObserver);
+  });
+}
+
+function makeFiles(count: number): FileDiff[] {
+  return Array.from({ length: count }, (_, i) => ({
+    oldPath: `file${i}.ts`,
+    newPath: `file${i}.ts`,
+    status: "modified" as const,
+    additions: 1,
+    deletions: 1,
+  }));
+}
+
+const defaultProps = {
+  phaseId: "phase-1",
+  commitMode: false,
+  commentsByLine: new Map(),
+  onAddComment: vi.fn(),
+  onResolveComment: vi.fn(),
+  onUnresolveComment: vi.fn(),
+};
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("DiffViewer", () => {
+  it("renders all FileCards when 5 files are all in viewport", () => {
+    const files = makeFiles(5);
+    render(<DiffViewer files={files} {...defaultProps} />);
+
+    // Trigger all five as intersecting
+    fireIntersection(files.map((f) => f.newPath));
+
+    expect(screen.getAllByTestId("file-card")).toHaveLength(5);
+  });
+
+  it("shows only intersecting FileCards for 300 files, placeholders for the rest", () => {
+    const files = makeFiles(300);
+    render(<DiffViewer files={files} {...defaultProps} />);
+
+    // Only first 5 files enter the viewport
+    fireIntersection(files.slice(0, 5).map((f) => f.newPath));
+
+    expect(screen.getAllByTestId("file-card")).toHaveLength(5);
+
+    // The remaining 295 should be 48px placeholder divs marked aria-hidden
+    const placeholders = document.querySelectorAll(
+      '[aria-hidden][style*="height: 48px"]',
+    );
+    expect(placeholders.length).toBeGreaterThanOrEqual(295);
+  });
+
+  it("skips IntersectionObserver for single-file diff and renders FileCard directly", () => {
+    render(<DiffViewer files={makeFiles(1)} {...defaultProps} />);
+
+    // Single-file path: isVisible is always true, no intersection event needed
+    expect(screen.getAllByTestId("file-card")).toHaveLength(1);
+  });
+
+  it("calls scrollIntoView on the wrapper div when onRegisterRef is used for sidebar navigation", () => {
+    const files = makeFiles(5);
+    const registeredRefs = new Map<string, HTMLDivElement>();
+    const onRegisterRef = (filePath: string, el: HTMLDivElement | null) => {
+      if (el) registeredRefs.set(filePath, el);
+    };
+
+    render(<DiffViewer files={files} {...defaultProps} onRegisterRef={onRegisterRef} />);
+
+    // All wrapper divs should have been registered (including the last one)
+    const targetFile = files[4].newPath;
+    expect(registeredRefs.has(targetFile)).toBe(true);
+
+    const wrapperEl = registeredRefs.get(targetFile)!;
+    const scrollSpy = vi.fn();
+    Object.defineProperty(wrapperEl, "scrollIntoView", { value: scrollSpy });
+
+    // Simulate a sidebar click that calls scrollIntoView on the wrapper
+    act(() => {
+      wrapperEl.scrollIntoView({ behavior: "smooth", block: "start" });
+    });
+    expect(scrollSpy).toHaveBeenCalledOnce();
+  });
+
+  it("fires getFileDiff queries in batches of 10 when expandAll is toggled", async () => {
+    const files = makeFiles(25); // 3 batches: 10, 10, 5
+    const { rerender } = render(
+      <DiffViewer files={files} {...defaultProps} expandAll={false} />,
+    );
+
+    rerender(<DiffViewer files={files} {...defaultProps} expandAll={true} />);
+
+    // Wait for all async batch iterations to complete
+    await act(async () => {
+      await new Promise((r) => setTimeout(r, 100));
+    });
+
+    // All 25 non-binary files should have been prefetched
+    expect(mockGetFileDiffFetch).toHaveBeenCalledTimes(25);
+  });
+});
diff --git a/apps/web/src/components/review/DiffViewer.tsx b/apps/web/src/components/review/DiffViewer.tsx
index 5b9c1e2..1387393 100644
--- a/apps/web/src/components/review/DiffViewer.tsx
+++ b/apps/web/src/components/review/DiffViewer.tsx
@@ -1,9 +1,25 @@
-import type { FileDiff, DiffLine, ReviewComment } from "./types";
+import { useCallback, useEffect, useRef, useState } from "react";
+import { useQueryClient } from "@tanstack/react-query";
+import type { FileDiff, FileDiffDetail, DiffLine, ReviewComment } from "./types";
 import { FileCard } from "./FileCard";
+import { trpc } from "@/lib/trpc";
+
+function getFileCommentMap(
+  commentsByLine: Map<string, ReviewComment[]>,
+  filePath: string,
+): Map<string, ReviewComment[]> {
+  const result = new Map<string, ReviewComment[]>();
+  for (const [key, val] of commentsByLine) {
+    if (key.startsWith(`${filePath}:`)) result.set(key, val);
+  }
+  return result;
+}
 
 interface DiffViewerProps {
-  files: FileDiff[];
-  comments: ReviewComment[];
+  files: (FileDiff | FileDiffDetail)[];
+  phaseId: string;
+  commitMode: boolean;
+  commentsByLine: Map<string, ReviewComment[]>;
   onAddComment: (
     filePath: string,
     lineNumber: number,
@@ -17,11 +33,14 @@ interface DiffViewerProps {
   viewedFiles?: Set<string>;
   onToggleViewed?: (filePath: string) => void;
   onRegisterRef?: (filePath: string, el: HTMLDivElement | null) => void;
+  expandAll?: boolean;
 }
 
 export function DiffViewer({
   files,
-  comments,
+  phaseId,
+  commitMode,
+  commentsByLine,
   onAddComment,
   onResolveComment,
   onUnresolveComment,
@@ -30,24 +49,156 @@ export function DiffViewer({
   viewedFiles,
   onToggleViewed,
   onRegisterRef,
+  expandAll,
 }: DiffViewerProps) {
+  // Set of file paths currently intersecting (or near) the viewport
+  const visibleFiles = useRef<Set<string>>(new Set());
+  // Map from filePath → wrapper div ref
+  const wrapperRefs = useRef<Map<string, HTMLDivElement>>(new Map());
+  // Increment to trigger re-render when visibility changes
+  const [visibilityVersion, setVisibilityVersion] = useState(0);
+
+  // Single IntersectionObserver for all wrappers
+  const observerRef = useRef<IntersectionObserver | null>(null);
+
+  useEffect(() => {
+    if (files.length === 1) return; // skip for single file
+
+    observerRef.current = new IntersectionObserver(
+      (entries) => {
+        let changed = false;
+        for (const entry of entries) {
+          const filePath = (entry.target as HTMLDivElement).dataset['filePath'];
+          if (!filePath) continue;
+          if (entry.isIntersecting) {
+            if (!visibleFiles.current.has(filePath)) {
+              visibleFiles.current.add(filePath);
+              changed = true;
+            }
+          } else {
+            if (visibleFiles.current.has(filePath)) {
+              visibleFiles.current.delete(filePath);
+              changed = true;
+            }
+          }
+        }
+        if (changed) setVisibilityVersion((v) => v + 1);
+      },
+      { rootMargin: '100% 0px 100% 0px' }, // 1× viewport above and below
+    );
+
+    // Observe all current wrapper divs
+    for (const el of wrapperRefs.current.values()) {
+      observerRef.current.observe(el);
+    }
+
+    return () => {
+      observerRef.current?.disconnect();
+    };
+  }, [files]); // re-create observer when file list changes
+
+  // Register wrapper ref — observes the div, registers with parent
+  const registerWrapper = useCallback(
+    (filePath: string, el: HTMLDivElement | null) => {
+      if (el) {
+        wrapperRefs.current.set(filePath, el);
+        observerRef.current?.observe(el);
+      } else {
+        const prev = wrapperRefs.current.get(filePath);
+        if (prev) observerRef.current?.unobserve(prev);
+        wrapperRefs.current.delete(filePath);
+      }
+      onRegisterRef?.(filePath, el);
+    },
+    [onRegisterRef],
+  );
+
+  // expandAll batch loading
+  const [expandedFiles, setExpandedFiles] = useState<Set<string>>(new Set());
+  const queryClient = useQueryClient();
+  const utils = trpc.useUtils();
+
+  useEffect(() => {
+    if (!expandAll || files.length === 0) return;
+
+    const BATCH = 10;
+    let cancelled = false;
+
+    async function batchExpand() {
+      const chunks: (FileDiff | FileDiffDetail)[][] = [];
+      for (let i = 0; i < files.length; i += BATCH) {
+        chunks.push(files.slice(i, i + BATCH));
+      }
+
+      for (const chunk of chunks) {
+        if (cancelled) break;
+        // Mark this batch as expanded (triggers FileCard renders + queries)
+        setExpandedFiles((prev) => {
+          const next = new Set(prev);
+          for (const f of chunk) {
+            if (f.status !== 'binary') next.add(f.newPath);
+          }
+          return next;
+        });
+        // Eagerly prefetch via React Query to saturate network
+        await Promise.all(
+          chunk
+            .filter((f) => f.status !== 'binary' && !('hunks' in f))
+            .map((f) =>
+              utils.getFileDiff
+                .fetch({ phaseId, filePath: encodeURIComponent(f.newPath) })
+                .catch(() => null), // swallow per-file errors; FileCard shows its own error state
+            ),
+        );
+      }
+    }
+
+    batchExpand();
+    return () => {
+      cancelled = true;
+    };
+  }, [expandAll]); // only re-run when expandAll toggles
+  // eslint-disable-next-line react-hooks/exhaustive-deps -- intentionally only on expandAll
+
+  // Suppress unused variable warning — used only to force re-render on visibility change
+  void visibilityVersion;
+  void queryClient; // imported for type alignment; actual prefetch goes through trpc utils
+
+  const isSingleFile = files.length === 1;
+
   return (
     <div className="space-y-4">
-      {files.map((file) => (
-        <div key={file.newPath} ref={(el) => onRegisterRef?.(file.newPath, el)}>
-          <FileCard
-            file={file}
-            comments={comments.filter((c) => c.filePath === file.newPath)}
-            onAddComment={onAddComment}
-            onResolveComment={onResolveComment}
-            onUnresolveComment={onUnresolveComment}
-            onReplyComment={onReplyComment}
-            onEditComment={onEditComment}
-            isViewed={viewedFiles?.has(file.newPath) ?? false}
-            onToggleViewed={() => onToggleViewed?.(file.newPath)}
-          />
-        </div>
-      ))}
+      {files.map((file) => {
+        const isVisible = isSingleFile || visibleFiles.current.has(file.newPath);
+        const isExpandedOverride = expandedFiles.has(file.newPath) ? true : undefined;
+        return (
+          <div
+            key={file.newPath}
+            ref={(el) => registerWrapper(file.newPath, el)}
+            data-file-path={file.newPath}
+          >
+            {isVisible ? (
+              <FileCard
+                file={file as FileDiff}
+                detail={'hunks' in file ? (file as FileDiffDetail) : undefined}
+                phaseId={phaseId}
+                commitMode={commitMode}
+                commentsByLine={getFileCommentMap(commentsByLine, file.newPath)}
+                isExpandedOverride={isExpandedOverride}
+                onAddComment={onAddComment}
+                onResolveComment={onResolveComment}
+                onUnresolveComment={onUnresolveComment}
+                onReplyComment={onReplyComment}
+                onEditComment={onEditComment}
+                isViewed={viewedFiles?.has(file.newPath) ?? false}
+                onToggleViewed={() => onToggleViewed?.(file.newPath)}
+              />
+            ) : (
+              <div style={{ height: '48px' }} aria-hidden />
+            )}
+          </div>
+        );
+      })}
     </div>
   );
 }
diff --git a/apps/web/src/components/review/FileCard.test.tsx b/apps/web/src/components/review/FileCard.test.tsx
new file mode 100644
index 0000000..56f73d5
--- /dev/null
+++ b/apps/web/src/components/review/FileCard.test.tsx
@@ -0,0 +1,270 @@
+// @vitest-environment happy-dom
+import "@testing-library/jest-dom/vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/react";
+import { vi, describe, it, expect, beforeEach } from "vitest";
+import { FileCard } from "./FileCard";
+import type { FileDiff, FileDiffDetail } from "./types";
+
+// ── Module mocks ──────────────────────────────────────────────────────────────
+
+vi.mock("./HunkRows", () => ({
+  HunkRows: ({ hunk }: { hunk: { header: string } }) => (
+    <tr data-testid="hunk-row">
+      <td>{hunk.header}</td>
+    </tr>
+  ),
+}));
+
+vi.mock("./use-syntax-highlight", () => ({
+  useHighlightedFile: () => null,
+}));
+
+// Hoist mocks so they can be referenced in vi.mock factories
+const { mockGetFileDiff, mockParseUnifiedDiff } = vi.hoisted(() => ({
+  mockGetFileDiff: vi.fn(),
+  mockParseUnifiedDiff: vi.fn(),
+}));
+
+vi.mock("@/lib/trpc", () => ({
+  trpc: {
+    getFileDiff: {
+      useQuery: (
+        input: unknown,
+        opts: { enabled: boolean; staleTime?: number },
+      ) => mockGetFileDiff(input, opts),
+    },
+  },
+}));
+
+vi.mock("./parse-diff", () => ({
+  parseUnifiedDiff: (rawDiff: string) => mockParseUnifiedDiff(rawDiff),
+}));
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeFile(overrides: Partial<FileDiff> = {}): FileDiff {
+  return {
+    oldPath: "src/foo.ts",
+    newPath: "src/foo.ts",
+    status: "modified",
+    additions: 10,
+    deletions: 5,
+    ...overrides,
+  };
+}
+
+const defaultProps = {
+  phaseId: "phase-1",
+  commitMode: false,
+  commentsByLine: new Map(),
+  onAddComment: vi.fn(),
+  onResolveComment: vi.fn(),
+  onUnresolveComment: vi.fn(),
+};
+
+beforeEach(() => {
+  mockGetFileDiff.mockReturnValue({
+    data: undefined,
+    isLoading: false,
+    isError: false,
+    refetch: vi.fn(),
+  });
+  // Default: return empty parse result
+  mockParseUnifiedDiff.mockReturnValue([]);
+});
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("FileCard", () => {
+  it("starts collapsed and does not enable getFileDiff query", () => {
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+
+    // Query must be called with enabled: false while card is collapsed
+    expect(mockGetFileDiff).toHaveBeenCalledWith(
+      expect.objectContaining({
+        filePath: encodeURIComponent("src/foo.ts"),
+      }),
+      expect.objectContaining({ enabled: false }),
+    );
+
+    // No hunk rows rendered in the collapsed state
+    expect(screen.queryByTestId("hunk-row")).toBeNull();
+  });
+
+  it("enables query and shows loading spinner when expanded", () => {
+    mockGetFileDiff.mockReturnValue({
+      data: undefined,
+      isLoading: true,
+      isError: false,
+      refetch: vi.fn(),
+    });
+
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+    fireEvent.click(screen.getByRole("button"));
+
+    // After expanding, query should be called with enabled: true
+    expect(mockGetFileDiff).toHaveBeenLastCalledWith(
+      expect.anything(),
+      expect.objectContaining({ enabled: true }),
+    );
+
+    // Loading spinner should be visible
+    expect(screen.getByText(/Loading diff/i)).toBeInTheDocument();
+  });
+
+  it("renders HunkRows when query succeeds", async () => {
+    mockGetFileDiff.mockReturnValue({
+      data: {
+        binary: false,
+        rawDiff:
+          "diff --git a/src/foo.ts b/src/foo.ts\n@@ -1,3 +1,3 @@\n context\n",
+      },
+      isLoading: false,
+      isError: false,
+      refetch: vi.fn(),
+    });
+
+    mockParseUnifiedDiff.mockReturnValue([
+      {
+        oldPath: "src/foo.ts",
+        newPath: "src/foo.ts",
+        status: "modified",
+        additions: 0,
+        deletions: 0,
+        hunks: [
+          {
+            header: "@@ -1,3 +1,3 @@",
+            oldStart: 1,
+            oldCount: 3,
+            newStart: 1,
+            newCount: 3,
+            lines: [],
+          },
+        ],
+      },
+    ]);
+
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+    fireEvent.click(screen.getByRole("button"));
+
+    await waitFor(() => {
+      expect(screen.getByTestId("hunk-row")).toBeInTheDocument();
+    });
+  });
+
+  it("shows error state with Retry button; clicking retry calls refetch", () => {
+    const refetch = vi.fn();
+    mockGetFileDiff.mockReturnValue({
+      data: undefined,
+      isLoading: false,
+      isError: true,
+      refetch,
+    });
+
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+    fireEvent.click(screen.getByRole("button"));
+
+    expect(screen.getByText(/Failed to load diff/i)).toBeInTheDocument();
+    const retryBtn = screen.getByRole("button", { name: /retry/i });
+    fireEvent.click(retryBtn);
+    expect(refetch).toHaveBeenCalledOnce();
+  });
+
+  it("shows binary message on expand and does not enable getFileDiff query", () => {
+    render(<FileCard file={makeFile({ status: "binary" })} {...defaultProps} />);
+    fireEvent.click(screen.getByRole("button"));
+
+    expect(screen.getByText(/Binary file/i)).toBeInTheDocument();
+
+    // Query must never be enabled for binary files
+    expect(mockGetFileDiff).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({ enabled: false }),
+    );
+  });
+
+  it("shows No content changes when parsed hunks array is empty", async () => {
+    mockGetFileDiff.mockReturnValue({
+      data: {
+        binary: false,
+        rawDiff: "diff --git a/src/foo.ts b/src/foo.ts\nsome content\n",
+      },
+      isLoading: false,
+      isError: false,
+      refetch: vi.fn(),
+    });
+
+    mockParseUnifiedDiff.mockReturnValue([
+      {
+        oldPath: "src/foo.ts",
+        newPath: "src/foo.ts",
+        status: "modified",
+        additions: 0,
+        deletions: 0,
+        hunks: [],
+      },
+    ]);
+
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+    fireEvent.click(screen.getByRole("button"));
+
+    await waitFor(() => {
+      expect(screen.getByText(/No content changes/i)).toBeInTheDocument();
+    });
+  });
+
+  it("renders pre-parsed hunks from detail prop without fetching", () => {
+    const detail: FileDiffDetail = {
+      oldPath: "src/foo.ts",
+      newPath: "src/foo.ts",
+      status: "modified",
+      additions: 5,
+      deletions: 2,
+      hunks: [
+        {
+          header: "@@ -1 +1 @@",
+          oldStart: 1,
+          oldCount: 1,
+          newStart: 1,
+          newCount: 1,
+          lines: [],
+        },
+      ],
+    };
+
+    render(<FileCard file={makeFile()} detail={detail} {...defaultProps} />);
+
+    // Should start expanded because detail prop is provided
+    expect(screen.getByTestId("hunk-row")).toBeInTheDocument();
+
+    // Query must not be enabled when detail prop is present
+    expect(mockGetFileDiff).toHaveBeenCalledWith(
+      expect.anything(),
+      expect.objectContaining({ enabled: false }),
+    );
+  });
+
+  it("does not refetch when collapsing and re-expanding", () => {
+    // Simulate data already available (as if previously fetched and cached)
+    mockGetFileDiff.mockReturnValue({
+      data: { binary: false, rawDiff: "" },
+      isLoading: false,
+      isError: false,
+      refetch: vi.fn(),
+    });
+
+    render(<FileCard file={makeFile()} {...defaultProps} />);
+    const headerBtn = screen.getByRole("button");
+
+    // Expand: query enabled, data shown immediately (no loading)
+    fireEvent.click(headerBtn);
+    expect(screen.queryByText(/Loading diff/i)).toBeNull();
+
+    // Collapse
+    fireEvent.click(headerBtn);
+
+    // Re-expand: should not enter loading state (data still available)
+    fireEvent.click(headerBtn);
+    expect(screen.queryByText(/Loading diff/i)).toBeNull();
+  });
+});
diff --git a/apps/web/src/components/review/FileCard.tsx b/apps/web/src/components/review/FileCard.tsx
index d7056c8..12cfb14 100644
--- a/apps/web/src/components/review/FileCard.tsx
+++ b/apps/web/src/components/review/FileCard.tsx
@@ -6,16 +6,16 @@ import {
   Minus,
   CheckCircle2,
   Circle,
+  Loader2,
 } from "lucide-react";
 import { Badge } from "@/components/ui/badge";
-import type { FileDiff, FileChangeType, DiffLine, ReviewComment } from "./types";
+import type { FileDiff, FileDiffDetail, DiffLine, ReviewComment } from "./types";
 import { HunkRows } from "./HunkRows";
 import { useHighlightedFile } from "./use-syntax-highlight";
+import { parseUnifiedDiff } from "./parse-diff";
+import { trpc } from "@/lib/trpc";
 
-const changeTypeBadge: Record<
-  FileChangeType,
-  { label: string; classes: string } | null
-> = {
+const statusBadge: Record<FileDiff['status'], { label: string; classes: string } | null> = {
   added: {
     label: "NEW",
     classes:
@@ -32,18 +32,27 @@ const changeTypeBadge: Record<
       "bg-status-active-bg text-status-active-fg border-status-active-border",
   },
   modified: null,
+  binary: {
+    label: "BINARY",
+    classes: "bg-muted text-muted-foreground border-border",
+  },
 };
 
-const leftBorderClass: Record<FileChangeType, string> = {
+const leftBorderClass: Record<FileDiff['status'], string> = {
   added: "border-l-2 border-l-status-success-fg",
   deleted: "border-l-2 border-l-status-error-fg",
   renamed: "border-l-2 border-l-status-active-fg",
   modified: "border-l-2 border-l-primary/40",
+  binary: "border-l-2 border-l-primary/40",
 };
 
 interface FileCardProps {
   file: FileDiff;
-  comments: ReviewComment[];
+  detail?: FileDiffDetail;
+  phaseId: string;
+  commitMode: boolean;
+  commentsByLine: Map<string, ReviewComment[]>;
+  isExpandedOverride?: boolean;
   onAddComment: (
     filePath: string,
     lineNumber: number,
@@ -60,7 +69,11 @@ interface FileCardProps {
 
 export function FileCard({
   file,
-  comments,
+  detail,
+  phaseId,
+  commitMode,
+  commentsByLine,
+  isExpandedOverride,
   onAddComment,
   onResolveComment,
   onUnresolveComment,
@@ -69,26 +82,65 @@ export function FileCard({
   isViewed = false,
   onToggleViewed = () => {},
 }: FileCardProps) {
-  const [expanded, setExpanded] = useState(true);
-  const commentCount = comments.length;
-  const badge = changeTypeBadge[file.changeType];
+  // Uncontrolled expand for normal file clicks.
+  // Start expanded if detail prop is provided (commit mode).
+  const [isExpandedLocal, setIsExpandedLocal] = useState(() => !!detail);
 
-  // Flatten all hunk lines for syntax highlighting
-  const allLines = useMemo(
-    () => file.hunks.flatMap((h) => h.lines),
-    [file.hunks],
+  // Merge with override from DiffViewer expandAll
+  const isExpanded = isExpandedOverride ?? isExpandedLocal;
+
+  const fileDiffQuery = trpc.getFileDiff.useQuery(
+    { phaseId, filePath: encodeURIComponent(file.newPath) },
+    {
+      enabled: isExpanded && !commitMode && file.status !== 'binary' && !detail,
+      staleTime: Infinity,
+    },
   );
+
+  // Compute hunks from query data (phase mode)
+  const parsedHunks = useMemo(() => {
+    if (!fileDiffQuery.data?.rawDiff) return null;
+    const parsed = parseUnifiedDiff(fileDiffQuery.data.rawDiff);
+    return parsed[0] ?? null;
+  }, [fileDiffQuery.data]);
+
+  // Collect all lines for syntax highlighting
+  const allLines = useMemo(() => {
+    if (detail) return detail.hunks.flatMap((h) => h.lines);
+    if (parsedHunks) return parsedHunks.hunks.flatMap((h) => h.lines);
+    return [];
+  }, [detail, parsedHunks]);
+
   const tokenMap = useHighlightedFile(file.newPath, allLines);
 
+  const commentCount = useMemo(() => {
+    let count = 0;
+    for (const [key, arr] of commentsByLine) {
+      if (key.startsWith(`${file.newPath}:`)) count += arr.length;
+    }
+    return count;
+  }, [commentsByLine, file.newPath]);
+
+  const badge = statusBadge[file.status];
+
+  const handlers = {
+    onAddComment,
+    onResolveComment,
+    onUnresolveComment,
+    onReplyComment,
+    onEditComment,
+    tokenMap,
+  };
+
   return (
     <div className="rounded-lg border border-border overflow-clip">
-      {/* File header — sticky so it stays visible when scrolling */}
+      {/* File header */}
       <button
-        className={`sticky z-10 flex w-full items-center gap-2 px-3 py-2 bg-muted hover:bg-muted/90 text-left text-sm font-mono transition-colors ${leftBorderClass[file.changeType]}`}
+        className={`sticky z-10 flex w-full items-center gap-2 px-3 py-2 bg-muted hover:bg-muted/90 text-left text-sm font-mono transition-colors ${leftBorderClass[file.status]}`}
         style={{ top: 'var(--review-header-h, 0px)' }}
-        onClick={() => setExpanded(!expanded)}
+        onClick={() => setIsExpandedLocal(!isExpandedLocal)}
       >
-        {expanded ? (
+        {isExpanded ? (
           <ChevronDown className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
         ) : (
           <ChevronRight className="h-3.5 w-3.5 shrink-0 text-muted-foreground" />
@@ -149,26 +201,63 @@ export function FileCard({
       </button>
 
       {/* Diff content */}
-      {expanded && (
+      {isExpanded && (
         <div className="overflow-x-auto">
-          <table className="w-full text-xs font-mono border-collapse">
-            <tbody>
-              {file.hunks.map((hunk, hi) => (
-                <HunkRows
-                  key={hi}
-                  hunk={hunk}
-                  filePath={file.newPath}
-                  comments={comments}
-                  onAddComment={onAddComment}
-                  onResolveComment={onResolveComment}
-                  onUnresolveComment={onUnresolveComment}
-                  onReplyComment={onReplyComment}
-                  onEditComment={onEditComment}
-                  tokenMap={tokenMap}
-                />
-              ))}
-            </tbody>
-          </table>
+          {detail ? (
+            // Commit mode: pre-parsed hunks from detail prop
+            detail.hunks.length === 0 ? (
+              <div className="px-4 py-3 text-xs text-muted-foreground">No content changes</div>
+            ) : (
+              <table className="w-full text-xs font-mono border-collapse">
+                <tbody>
+                  {detail.hunks.map((hunk, hi) => (
+                    <HunkRows
+                      key={hi}
+                      hunk={hunk}
+                      filePath={file.newPath}
+                      commentsByLine={commentsByLine}
+                      {...handlers}
+                    />
+                  ))}
+                </tbody>
+              </table>
+            )
+          ) : file.status === 'binary' ? (
+            <div className="px-4 py-3 text-xs text-muted-foreground">Binary file — diff not shown</div>
+          ) : fileDiffQuery.isLoading ? (
+            <div className="flex items-center gap-2 px-4 py-3 text-xs text-muted-foreground">
+              <Loader2 className="h-3.5 w-3.5 animate-spin" />
+              Loading diff…
+            </div>
+          ) : fileDiffQuery.isError ? (
+            <div className="flex items-center gap-2 px-4 py-3 text-xs text-destructive">
+              Failed to load diff.
+              <button
+                className="underline hover:no-underline"
+                onClick={() => fileDiffQuery.refetch()}
+              >
+                Retry
+              </button>
+            </div>
+          ) : fileDiffQuery.data ? (
+            !parsedHunks || parsedHunks.hunks.length === 0 ? (
+              <div className="px-4 py-3 text-xs text-muted-foreground">No content changes</div>
+            ) : (
+              <table className="w-full text-xs font-mono border-collapse">
+                <tbody>
+                  {parsedHunks.hunks.map((hunk, hi) => (
+                    <HunkRows
+                      key={hi}
+                      hunk={hunk}
+                      filePath={file.newPath}
+                      commentsByLine={commentsByLine}
+                      {...handlers}
+                    />
+                  ))}
+                </tbody>
+              </table>
+            )
+          ) : null}
         </div>
       )}
     </div>
diff --git a/apps/web/src/components/review/HunkRows.tsx b/apps/web/src/components/review/HunkRows.tsx
index 86cf6dd..9bec866 100644
--- a/apps/web/src/components/review/HunkRows.tsx
+++ b/apps/web/src/components/review/HunkRows.tsx
@@ -6,7 +6,7 @@ import type { LineTokenMap } from "./use-syntax-highlight";
 interface HunkRowsProps {
   hunk: { header: string; lines: DiffLine[] };
   filePath: string;
-  comments: ReviewComment[];
+  commentsByLine: Map<string, ReviewComment[]>;
   onAddComment: (
     filePath: string,
     lineNumber: number,
@@ -23,7 +23,7 @@ interface HunkRowsProps {
 export function HunkRows({
   hunk,
   filePath,
-  comments,
+  commentsByLine,
   onAddComment,
   onResolveComment,
   onUnresolveComment,
@@ -81,9 +81,9 @@ export function HunkRows({
 
       {hunk.lines.map((line, li) => {
         const lineKey = line.newLineNumber ?? line.oldLineNumber ?? li;
-        const lineComments = comments.filter(
-          (c) => c.lineNumber === lineKey && c.lineType === line.type,
-        );
+        // O(1) map lookup — replaces the previous O(n) filter
+        const lineComments =
+          commentsByLine.get(`${filePath}:${lineKey}:${line.type}`) ?? [];
         const isCommenting =
           commentingLine?.lineNumber === lineKey &&
           commentingLine?.lineType === line.type;
diff --git a/apps/web/src/components/review/InitiativeReview.tsx b/apps/web/src/components/review/InitiativeReview.tsx
index d188005..ef9779c 100644
--- a/apps/web/src/components/review/InitiativeReview.tsx
+++ b/apps/web/src/components/review/InitiativeReview.tsx
@@ -308,7 +308,7 @@ export function InitiativeReview({ initiativeId, onCompleted }: InitiativeReview
           ) : (
             <DiffViewer
               files={files}
-              comments={[]}
+              commentsByLine={new Map()}
               onAddComment={() => {}}
               onResolveComment={() => {}}
               onUnresolveComment={() => {}}
diff --git a/apps/web/src/components/review/ReviewHeader.tsx b/apps/web/src/components/review/ReviewHeader.tsx
index 44e55fc..44cc260 100644
--- a/apps/web/src/components/review/ReviewHeader.tsx
+++ b/apps/web/src/components/review/ReviewHeader.tsx
@@ -42,6 +42,9 @@ interface ReviewHeaderProps {
   preview: PreviewState | null;
   viewedCount?: number;
   totalCount?: number;
+  totalAdditions?: number;
+  totalDeletions?: number;
+  onExpandAll?: () => void;
 }
 
 export function ReviewHeader({
@@ -62,9 +65,12 @@ export function ReviewHeader({
   preview,
   viewedCount,
   totalCount,
+  totalAdditions: totalAdditionsProp,
+  totalDeletions: totalDeletionsProp,
+  onExpandAll,
 }: ReviewHeaderProps) {
-  const totalAdditions = files.reduce((s, f) => s + f.additions, 0);
-  const totalDeletions = files.reduce((s, f) => s + f.deletions, 0);
+  const totalAdditions = totalAdditionsProp ?? files.reduce((s, f) => s + f.additions, 0);
+  const totalDeletions = totalDeletionsProp ?? files.reduce((s, f) => s + f.deletions, 0);
   const [showConfirmation, setShowConfirmation] = useState(false);
   const [showRequestConfirm, setShowRequestConfirm] = useState(false);
   const confirmRef = useRef<HTMLDivElement>(null);
@@ -186,6 +192,16 @@ export function ReviewHeader({
 
         {/* Right: preview + actions */}
         <div className="flex items-center gap-3 shrink-0">
+          {onExpandAll && (
+            <Button
+              variant="ghost"
+              size="sm"
+              onClick={onExpandAll}
+              className="h-7 text-xs px-2 text-muted-foreground"
+            >
+              Expand all
+            </Button>
+          )}
           {/* Preview controls */}
           {preview && <PreviewControls preview={preview} />}
 
diff --git a/apps/web/src/components/review/ReviewSidebar.test.tsx b/apps/web/src/components/review/ReviewSidebar.test.tsx
new file mode 100644
index 0000000..f4b5644
--- /dev/null
+++ b/apps/web/src/components/review/ReviewSidebar.test.tsx
@@ -0,0 +1,193 @@
+// @vitest-environment happy-dom
+import '@testing-library/jest-dom/vitest';
+import { render, screen, fireEvent, act } from '@testing-library/react';
+import { vi, describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { ReviewSidebar } from './ReviewSidebar';
+import type { FileDiff, ReviewComment, CommitInfo } from './types';
+
+// Mock ResizeObserver — not provided by happy-dom.
+// react-window 2.x uses `new ResizeObserver()` internally.
+class MockResizeObserver {
+  observe() {}
+  unobserve() {}
+  disconnect() {}
+}
+vi.stubGlobal('ResizeObserver', MockResizeObserver);
+
+// Mock react-window to avoid ESM/CJS duplicate-React-instance errors in Vitest.
+// The mock renders only the first 15 rows, simulating windowed rendering.
+// It also exposes a `listRef`-compatible imperative handle so scroll-save/restore logic runs.
+vi.mock('react-window', () => ({
+  List: vi.fn(({ rowComponent: RowComponent, rowCount, rowProps, listRef }: any) => {
+    // Expose the imperative API via the ref (synchronous assignment is safe in tests).
+    if (listRef && typeof listRef === 'object' && 'current' in listRef) {
+      listRef.current = { element: { scrollTop: 0 }, scrollToRow: vi.fn() };
+    }
+    const renderCount = Math.min(rowCount ?? 0, 15);
+    return (
+      <div data-testid="virtual-list">
+        {Array.from({ length: renderCount }, (_, i) => (
+          <RowComponent key={i} index={i} style={{}} ariaAttributes={{}} {...rowProps} />
+        ))}
+      </div>
+    );
+  }),
+}));
+
+// ─── Helpers ──────────────────────────────────────────────────────────────────
+
+function makeFile(path: string): FileDiff {
+  return {
+    oldPath: path,
+    newPath: path,
+    hunks: [],
+    additions: 1,
+    deletions: 0,
+    changeType: 'modified',
+  };
+}
+
+function makeFiles(count: number, prefix = 'src/components/'): FileDiff[] {
+  return Array.from({ length: count }, (_, i) =>
+    makeFile(`${prefix}file${String(i).padStart(4, '0')}.ts`),
+  );
+}
+
+const NO_COMMENTS: ReviewComment[] = [];
+const NO_COMMITS: CommitInfo[] = [];
+
+function renderSidebar(files: FileDiff[]) {
+  return render(
+    <ReviewSidebar
+      files={files}
+      comments={NO_COMMENTS}
+      onFileClick={vi.fn()}
+      selectedCommit={null}
+      activeFiles={files}
+      commits={NO_COMMITS}
+      onSelectCommit={vi.fn()}
+    />,
+  );
+}
+
+// ─── Tests ────────────────────────────────────────────────────────────────────
+
+describe('ReviewSidebar FilesView virtualization', () => {
+  beforeEach(() => vi.clearAllMocks());
+  afterEach(() => vi.restoreAllMocks());
+
+  // 1. Virtual list NOT used for ≤50 files (fallback path)
+  it('does not use virtual list when files count is ≤50', () => {
+    renderSidebar(makeFiles(10));
+
+    expect(screen.queryByTestId('virtual-list')).not.toBeInTheDocument();
+    // All 10 file rows are in the DOM directly
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBe(10);
+  });
+
+  // 2. Virtual list IS used for >50 files (virtualized path)
+  it('uses virtual list when files count is >50', () => {
+    renderSidebar(makeFiles(1000));
+
+    expect(screen.getByTestId('virtual-list')).toBeInTheDocument();
+    // Mock renders only 15 rows — far fewer than 1000
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBeLessThan(50);
+  });
+
+  // 3. Directory collapse removes file rows from the virtual list
+  it('removes file rows from virtual list when directory is collapsed', async () => {
+    // 100 files all in "src/" — produces 101 rows (1 dir-header + 100 files), which is >50
+    const files = Array.from({ length: 100 }, (_, i) => makeFile(`src/file${i}.ts`));
+    renderSidebar(files);
+
+    expect(screen.getByTestId('virtual-list')).toBeInTheDocument();
+
+    const dirHeader = screen.getByRole('button', { name: /src\// });
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBeGreaterThan(0);
+
+    await act(async () => {
+      fireEvent.click(dirHeader);
+    });
+
+    // After collapse: only the dir-header row remains in the virtual list
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBe(0);
+    expect(document.querySelectorAll('[data-testid="dir-header"]').length).toBe(1);
+  });
+
+  // 3a. Expanding a collapsed directory restores file rows
+  it('restores file rows when a collapsed directory is expanded again', async () => {
+    const files = makeFiles(60, 'src/components/');
+    renderSidebar(files);
+
+    const dirHeader = screen.getByRole('button', { name: /src\/components\// });
+
+    // Collapse
+    await act(async () => {
+      fireEvent.click(dirHeader);
+    });
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBe(0);
+
+    // Expand again
+    const freshDirHeader = screen.getByRole('button', { name: /src\/components\// });
+    await act(async () => {
+      fireEvent.click(freshDirHeader);
+    });
+
+    // File rows are back (virtual list renders up to 15)
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBeGreaterThan(0);
+    expect(document.querySelectorAll('[data-testid="dir-header"]').length).toBeGreaterThan(0);
+  });
+
+  // 4. Scroll position saved and restored on Files ↔ Commits tab switch
+  it('restores file rows when returning to Files tab after switching to Commits tab', async () => {
+    renderSidebar(makeFiles(200));
+
+    // Files tab is default — file rows are visible
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBeGreaterThan(0);
+
+    // Switch to Commits tab — FilesView unmounts (scroll offset is saved)
+    await act(async () => {
+      fireEvent.click(screen.getByTitle('Commits'));
+    });
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBe(0);
+
+    // Switch back to Files tab — FilesView remounts (scroll offset is restored)
+    await act(async () => {
+      fireEvent.click(screen.getByTitle('Files'));
+    });
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBeGreaterThan(0);
+  });
+
+  // 5. Clicking a file calls onFileClick with the correct path
+  it('calls onFileClick when a file row is clicked', () => {
+    const onFileClick = vi.fn();
+    const files = makeFiles(5);
+    render(
+      <ReviewSidebar
+        files={files}
+        comments={NO_COMMENTS}
+        onFileClick={onFileClick}
+        selectedCommit={null}
+        activeFiles={files}
+        commits={NO_COMMITS}
+        onSelectCommit={vi.fn()}
+      />,
+    );
+
+    const fileButtons = document.querySelectorAll('[data-testid="file-row"]');
+    expect(fileButtons.length).toBeGreaterThan(0);
+    fireEvent.click(fileButtons[0]);
+
+    // First file after alphabetical sort within the directory
+    expect(onFileClick).toHaveBeenCalledWith(files[0].newPath);
+  });
+
+  // 6. Root-level files (no subdirectory) render without a directory header
+  it('root-level files render without a directory header', () => {
+    const files = makeFiles(10, ''); // no prefix → root-level files
+    renderSidebar(files);
+
+    expect(document.querySelectorAll('[data-testid="file-row"]').length).toBe(10);
+    expect(document.querySelectorAll('[data-testid="dir-header"]').length).toBe(0);
+  });
+});
diff --git a/apps/web/src/components/review/ReviewSidebar.tsx b/apps/web/src/components/review/ReviewSidebar.tsx
index 4e344d1..5271d15 100644
--- a/apps/web/src/components/review/ReviewSidebar.tsx
+++ b/apps/web/src/components/review/ReviewSidebar.tsx
@@ -1,8 +1,15 @@
-import { useMemo, useState } from "react";
+import { useMemo, useState, useRef, useEffect, useCallback } from "react";
+// Using react-window 2.x (installed version). The task spec was written for react-window 1.x
+// (VariableSizeList API). react-window 2.x provides a `List` component with a different but
+// equivalent API: it handles ResizeObserver internally (no explicit height/width props needed),
+// uses `rowComponent`/`rowProps` for rendering, and exposes `scrollToRow` via `listRef`.
+import { List } from "react-window";
+import type { RowComponentProps, ListImperativeAPI } from "react-window";
 import {
   MessageSquare,
   FileCode,
   FolderOpen,
+  ChevronRight,
   Plus,
   Minus,
   Circle,
@@ -38,6 +45,8 @@ export function ReviewSidebar({
   viewedFiles = new Set(),
 }: ReviewSidebarProps) {
   const [view, setView] = useState<SidebarView>("files");
+  // Persist Files-tab scroll offset across Files ↔ Commits switches
+  const filesScrollOffsetRef = useRef<number>(0);
 
   return (
     <div className="flex h-full">
@@ -58,8 +67,8 @@ export function ReviewSidebar({
         />
       </div>
 
-      {/* Content panel */}
-      <div className="flex-1 min-w-0 overflow-y-auto p-4">
+      {/* Content panel — flex column so FilesView can stretch and manage its own scroll */}
+      <div className="flex-1 min-w-0 flex flex-col min-h-0">
         {view === "files" ? (
           <FilesView
             files={files}
@@ -69,13 +78,16 @@ export function ReviewSidebar({
             selectedCommit={selectedCommit}
             activeFiles={activeFiles}
             viewedFiles={viewedFiles}
+            scrollOffsetRef={filesScrollOffsetRef}
           />
         ) : (
-          <CommitsView
-            commits={commits}
-            selectedCommit={selectedCommit}
-            onSelectCommit={onSelectCommit}
-          />
+          <div className="overflow-y-auto p-4 flex-1">
+            <CommitsView
+              commits={commits}
+              selectedCommit={selectedCommit}
+              onSelectCommit={onSelectCommit}
+            />
+          </div>
         )}
       </div>
     </div>
@@ -171,6 +183,109 @@ const changeTypeDotColor: Record<string, string> = {
   renamed: "bg-status-active-fg",
 };
 
+// ─── Row type for virtualized list ───
+
+type Row =
+  | { kind: "dir-header"; dirName: string; fileCount: number; isCollapsed: boolean }
+  | { kind: "file"; file: FileDiff; dirName: string; isViewed: boolean; commentCount: number };
+
+// Item heights: dir-header ≈ 32px (py-0.5 + icon), file row ≈ 40px (py-1 + text)
+const DIR_HEADER_HEIGHT = 32;
+const FILE_ROW_HEIGHT = 40;
+
+// ─── Virtualized row component (must be stable — defined outside FilesView) ───
+
+type VirtualRowProps = {
+  rows: Row[];
+  selectedCommit: string | null;
+  activeFilePaths: Set<string>;
+  onFileClick: (filePath: string) => void;
+  onToggleDir: (dirName: string) => void;
+};
+
+function VirtualRowItem({
+  index,
+  style,
+  rows,
+  selectedCommit,
+  activeFilePaths,
+  onFileClick,
+  onToggleDir,
+}: RowComponentProps<VirtualRowProps>) {
+  const row = rows[index];
+  if (!row) return null;
+
+  if (row.kind === "dir-header") {
+    return (
+      <button
+        data-testid="dir-header"
+        style={style}
+        className="flex w-full items-center gap-1 text-[10px] font-mono text-muted-foreground/70 px-2 hover:bg-accent/30 transition-colors"
+        onClick={() => onToggleDir(row.dirName)}
+        title={row.isCollapsed ? "Expand directory" : "Collapse directory"}
+      >
+        <ChevronRight
+          className={`h-3 w-3 shrink-0 transition-transform ${row.isCollapsed ? "" : "rotate-90"}`}
+        />
+        <FolderOpen className="h-3 w-3 shrink-0" />
+        <span className="truncate">{row.dirName}</span>
+      </button>
+    );
+  }
+
+  // kind === "file"
+  const { file, dirName, isViewed, commentCount } = row;
+  const isInView = activeFilePaths.has(file.newPath);
+  const dimmed = selectedCommit && !isInView;
+  const dotColor = changeTypeDotColor[file.changeType];
+
+  return (
+    <button
+      data-testid="file-row"
+      style={style}
+      className={`
+        flex w-full items-center gap-1.5 rounded py-1 text-left text-[11px]
+        hover:bg-accent/50 transition-colors group
+        ${dirName ? "pl-4 pr-2" : "px-2"}
+        ${dimmed ? "opacity-35" : ""}
+      `}
+      onClick={() => onFileClick(file.newPath)}
+    >
+      {isViewed ? (
+        <CheckCircle2 className="h-3 w-3 text-status-success-fg shrink-0" />
+      ) : (
+        <FileCode className="h-3 w-3 text-muted-foreground shrink-0" />
+      )}
+      {dotColor && (
+        <span className={`h-1.5 w-1.5 rounded-full shrink-0 ${dotColor}`} />
+      )}
+      <span className="truncate flex-1 font-mono">
+        {getFileName(file.newPath)}
+      </span>
+      <span className="flex items-center gap-1 shrink-0">
+        {commentCount > 0 && (
+          <span className="flex items-center gap-0.5 text-muted-foreground">
+            <MessageSquare className="h-2.5 w-2.5" />
+            {commentCount}
+          </span>
+        )}
+        {file.additions > 0 && (
+          <span className="text-diff-add-fg text-[10px]">
+            <Plus className="h-2.5 w-2.5 inline" />
+            {file.additions}
+          </span>
+        )}
+        {file.deletions > 0 && (
+          <span className="text-diff-remove-fg text-[10px]">
+            <Minus className="h-2.5 w-2.5 inline" />
+            {file.deletions}
+          </span>
+        )}
+      </span>
+    </button>
+  );
+}
+
 function FilesView({
   files,
   comments,
@@ -179,6 +294,7 @@ function FilesView({
   selectedCommit,
   activeFiles,
   viewedFiles,
+  scrollOffsetRef,
 }: {
   files: FileDiff[];
   comments: ReviewComment[];
@@ -187,10 +303,14 @@ function FilesView({
   selectedCommit: string | null;
   activeFiles: FileDiff[];
   viewedFiles: Set<string>;
+  scrollOffsetRef: React.MutableRefObject<number>;
 }) {
   const unresolvedCount = comments.filter((c) => !c.resolved && !c.parentCommentId).length;
   const resolvedCount = comments.filter((c) => c.resolved && !c.parentCommentId).length;
-  const activeFilePaths = new Set(activeFiles.map((f) => f.newPath));
+  const activeFilePaths = useMemo(
+    () => new Set(activeFiles.map((f) => f.newPath)),
+    [activeFiles],
+  );
 
   const directoryGroups = useMemo(() => groupFilesByDirectory(files), [files]);
 
@@ -198,169 +318,308 @@ function FilesView({
   const totalCount = files.length;
   const progressPercent = totalCount > 0 ? (viewedCount / totalCount) * 100 : 0;
 
+  // ─── Collapse state ───
+  const [collapsedDirs, setCollapsedDirs] = useState<Set<string>>(new Set());
+
+  const toggleDir = useCallback((dirName: string) => {
+    setCollapsedDirs((prev) => {
+      const next = new Set(prev);
+      if (next.has(dirName)) next.delete(dirName);
+      else next.add(dirName);
+      return next;
+    });
+  }, []);
+
+  // ─── Flat row list for virtualization ───
+  const rows = useMemo<Row[]>(() => {
+    const result: Row[] = [];
+    for (const group of directoryGroups) {
+      const isCollapsed = collapsedDirs.has(group.directory);
+      // Root-level files (directory === "") get no dir-header, preserving existing behavior
+      if (group.directory) {
+        result.push({
+          kind: "dir-header",
+          dirName: group.directory,
+          fileCount: group.files.length,
+          isCollapsed,
+        });
+      }
+      if (!isCollapsed) {
+        for (const file of group.files) {
+          const commentCount = comments.filter(
+            (c) => c.filePath === file.newPath && !c.parentCommentId,
+          ).length;
+          result.push({
+            kind: "file",
+            file,
+            dirName: group.directory,
+            isViewed: viewedFiles.has(file.newPath),
+            commentCount,
+          });
+        }
+      }
+    }
+    return result;
+  }, [directoryGroups, collapsedDirs, comments, viewedFiles]);
+
+  const isVirtualized = rows.length > 50;
+
+  // ─── react-window 2.x imperative ref ───
+  const listRef = useRef<ListImperativeAPI | null>(null);
+  // Fallback container ref for non-virtualized path
+  const containerRef = useRef<HTMLDivElement | null>(null);
+
+  // Restore scroll position on mount (both paths)
+  useEffect(() => {
+    const offset = scrollOffsetRef.current;
+    if (!offset) return;
+    if (isVirtualized) {
+      // react-window 2.x: scroll via the outermost DOM element
+      const el = listRef.current?.element;
+      if (el) el.scrollTop = offset;
+    } else if (containerRef.current) {
+      containerRef.current.scrollTop = offset;
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []); // only on mount
+
+  // Save scroll position on unmount (both paths)
+  useEffect(() => {
+    return () => {
+      if (isVirtualized) {
+        scrollOffsetRef.current = listRef.current?.element?.scrollTop ?? 0;
+      } else {
+        scrollOffsetRef.current = containerRef.current?.scrollTop ?? 0;
+      }
+    };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [isVirtualized]);
+
+  // Row height function for react-window 2.x List
+  const rowHeight = useCallback(
+    (index: number) => (rows[index]?.kind === "dir-header" ? DIR_HEADER_HEIGHT : FILE_ROW_HEIGHT),
+    [rows],
+  );
+
+  // Handle file click: call onFileClick and scroll virtual list to row
+  const handleFileClick = useCallback(
+    (filePath: string) => {
+      onFileClick(filePath);
+      const rowIndex = rows.findIndex(
+        (r) => r.kind === "file" && r.file.newPath === filePath,
+      );
+      if (rowIndex >= 0) {
+        listRef.current?.scrollToRow({ index: rowIndex, align: "smart" });
+      }
+    },
+    [onFileClick, rows, listRef],
+  );
+
+  // Stable row props for the virtual row component
+  const rowProps = useMemo<VirtualRowProps>(
+    () => ({
+      rows,
+      selectedCommit,
+      activeFilePaths,
+      onFileClick: handleFileClick,
+      onToggleDir: toggleDir,
+    }),
+    [rows, selectedCommit, activeFilePaths, handleFileClick, toggleDir],
+  );
+
   return (
-    <div className="space-y-4">
-      {/* Review progress */}
-      {totalCount > 0 && (
-        <div className="space-y-1.5">
-          <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider">
-            Review Progress
-          </h4>
-          <div className="h-1 rounded-full bg-muted w-full">
-            <div
-              className="h-full rounded-full bg-status-success-fg transition-all duration-300"
-              style={{ width: `${progressPercent}%` }}
-            />
-          </div>
-          <span className="text-[10px] text-muted-foreground">
-            {viewedCount}/{totalCount} files viewed
-          </span>
-        </div>
-      )}
-
-      {/* Discussions — individual threads */}
-      {comments.length > 0 && (
-        <div className="space-y-1.5">
-          <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider flex items-center justify-between">
-            <span>Discussions</span>
-            <span className="flex items-center gap-2 font-normal normal-case">
-              {unresolvedCount > 0 && (
-                <span className="flex items-center gap-0.5 text-status-warning-fg">
-                  <Circle className="h-2.5 w-2.5" />
-                  {unresolvedCount}
-                </span>
-              )}
-              {resolvedCount > 0 && (
-                <span className="flex items-center gap-0.5 text-status-success-fg">
-                  <CheckCircle2 className="h-2.5 w-2.5" />
-                  {resolvedCount}
-                </span>
-              )}
+    <div className="flex flex-col h-full min-h-0">
+      {/* Fixed header — review progress + discussions */}
+      <div className="p-4 space-y-4 shrink-0">
+        {/* Review progress */}
+        {totalCount > 0 && (
+          <div className="space-y-1.5">
+            <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider">
+              Review Progress
+            </h4>
+            <div className="h-1 rounded-full bg-muted w-full">
+              <div
+                className="h-full rounded-full bg-status-success-fg transition-all duration-300"
+                style={{ width: `${progressPercent}%` }}
+              />
+            </div>
+            <span className="text-[10px] text-muted-foreground">
+              {viewedCount}/{totalCount} files viewed
             </span>
-          </h4>
-          <div className="space-y-0.5">
-            {comments
-              .filter((c) => !c.parentCommentId)
-              .map((thread) => {
-                const replyCount = comments.filter(
-                  (c) => c.parentCommentId === thread.id,
-                ).length;
-                return (
-                  <button
-                    key={thread.id}
-                    className={`
-                      flex w-full flex-col gap-0.5 rounded px-2 py-1.5 text-left
-                      transition-colors hover:bg-accent/50
-                      ${thread.resolved ? "opacity-50" : ""}
-                    `}
-                    onClick={() => onCommentClick ? onCommentClick(thread.id) : onFileClick(thread.filePath)}
-                  >
-                    <div className="flex items-center gap-1.5 w-full min-w-0">
-                      {thread.resolved ? (
-                        <CheckCircle2 className="h-3 w-3 text-status-success-fg shrink-0" />
-                      ) : (
-                        <MessageSquare className="h-3 w-3 text-status-warning-fg shrink-0" />
-                      )}
-                      <span className="text-[10px] font-mono text-muted-foreground truncate">
-                        {getFileName(thread.filePath)}:{thread.lineNumber}
-                      </span>
-                      {replyCount > 0 && (
-                        <span className="text-[9px] text-muted-foreground/70 shrink-0 ml-auto">
-                          {replyCount}
-                        </span>
-                      )}
-                    </div>
-                    <span className="text-[11px] text-foreground/80 truncate pl-[18px]">
-                      {thread.body.length > 60
-                        ? thread.body.slice(0, 57) + "..."
-                        : thread.body}
-                    </span>
-                  </button>
-                );
-              })}
           </div>
-        </div>
-      )}
+        )}
 
-      {/* Directory-grouped file tree */}
-      <div>
-        <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider mb-1.5">
-          Files
-          {selectedCommit && (
-            <span className="font-normal ml-1 normal-case">
-              ({activeFiles.length} in commit)
-            </span>
-          )}
-        </h4>
-        {directoryGroups.map((group) => (
-          <div key={group.directory}>
-            {/* Directory header */}
-            {group.directory && (
-              <div className="text-[10px] font-mono text-muted-foreground/70 mt-2 first:mt-0 px-2 py-0.5 flex items-center gap-1">
-                <FolderOpen className="h-3 w-3 shrink-0" />
-                <span className="truncate">{group.directory}</span>
-              </div>
-            )}
-            {/* Files in directory */}
+        {/* Discussions — individual threads */}
+        {comments.length > 0 && (
+          <div className="space-y-1.5">
+            <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider flex items-center justify-between">
+              <span>Discussions</span>
+              <span className="flex items-center gap-2 font-normal normal-case">
+                {unresolvedCount > 0 && (
+                  <span className="flex items-center gap-0.5 text-status-warning-fg">
+                    <Circle className="h-2.5 w-2.5" />
+                    {unresolvedCount}
+                  </span>
+                )}
+                {resolvedCount > 0 && (
+                  <span className="flex items-center gap-0.5 text-status-success-fg">
+                    <CheckCircle2 className="h-2.5 w-2.5" />
+                    {resolvedCount}
+                  </span>
+                )}
+              </span>
+            </h4>
             <div className="space-y-0.5">
-              {group.files.map((file) => {
-                const fileCommentCount = comments.filter(
-                  (c) => c.filePath === file.newPath && !c.parentCommentId,
-                ).length;
-                const isInView = activeFilePaths.has(file.newPath);
-                const dimmed = selectedCommit && !isInView;
-                const isViewed = viewedFiles.has(file.newPath);
-                const dotColor = changeTypeDotColor[file.changeType];
-
-                return (
-                  <button
-                    key={file.newPath}
-                    className={`
-                      flex w-full items-center gap-1.5 rounded py-1 text-left text-[11px]
-                      hover:bg-accent/50 transition-colors group
-                      ${group.directory ? "pl-4 pr-2" : "px-2"}
-                      ${dimmed ? "opacity-35" : ""}
-                    `}
-                    onClick={() => onFileClick(file.newPath)}
-                  >
-                    {isViewed ? (
-                      <CheckCircle2 className="h-3 w-3 text-status-success-fg shrink-0" />
-                    ) : (
-                      <FileCode className="h-3 w-3 text-muted-foreground shrink-0" />
-                    )}
-                    {dotColor && (
-                      <span className={`h-1.5 w-1.5 rounded-full shrink-0 ${dotColor}`} />
-                    )}
-                    <span className="truncate flex-1 font-mono">
-                      {getFileName(file.newPath)}
-                    </span>
-                    <span className="flex items-center gap-1 shrink-0">
-                      {fileCommentCount > 0 && (
-                        <span className="flex items-center gap-0.5 text-muted-foreground">
-                          <MessageSquare className="h-2.5 w-2.5" />
-                          {fileCommentCount}
+              {comments
+                .filter((c) => !c.parentCommentId)
+                .map((thread) => {
+                  const replyCount = comments.filter(
+                    (c) => c.parentCommentId === thread.id,
+                  ).length;
+                  return (
+                    <button
+                      key={thread.id}
+                      className={`
+                        flex w-full flex-col gap-0.5 rounded px-2 py-1.5 text-left
+                        transition-colors hover:bg-accent/50
+                        ${thread.resolved ? "opacity-50" : ""}
+                      `}
+                      onClick={() => onCommentClick ? onCommentClick(thread.id) : onFileClick(thread.filePath)}
+                    >
+                      <div className="flex items-center gap-1.5 w-full min-w-0">
+                        {thread.resolved ? (
+                          <CheckCircle2 className="h-3 w-3 text-status-success-fg shrink-0" />
+                        ) : (
+                          <MessageSquare className="h-3 w-3 text-status-warning-fg shrink-0" />
+                        )}
+                        <span className="text-[10px] font-mono text-muted-foreground truncate">
+                          {getFileName(thread.filePath)}:{thread.lineNumber}
                         </span>
-                      )}
-                      {file.additions > 0 && (
-                        <span className="text-diff-add-fg text-[10px]">
-                          <Plus className="h-2.5 w-2.5 inline" />
-                          {file.additions}
-                        </span>
-                      )}
-                      {file.deletions > 0 && (
-                        <span className="text-diff-remove-fg text-[10px]">
-                          <Minus className="h-2.5 w-2.5 inline" />
-                          {file.deletions}
-                        </span>
-                      )}
-                    </span>
-                  </button>
-                );
-              })}
+                        {replyCount > 0 && (
+                          <span className="text-[9px] text-muted-foreground/70 shrink-0 ml-auto">
+                            {replyCount}
+                          </span>
+                        )}
+                      </div>
+                      <span className="text-[11px] text-foreground/80 truncate pl-[18px]">
+                        {thread.body.length > 60
+                          ? thread.body.slice(0, 57) + "..."
+                          : thread.body}
+                      </span>
+                    </button>
+                  );
+                })}
             </div>
           </div>
-        ))}
+        )}
+
+        {/* Files section heading */}
+        <div>
+          <h4 className="text-[10px] font-semibold text-muted-foreground uppercase tracking-wider mb-1.5">
+            Files
+            {selectedCommit && (
+              <span className="font-normal ml-1 normal-case">
+                ({activeFiles.length} in commit)
+              </span>
+            )}
+          </h4>
+        </div>
       </div>
+
+      {/* Scrollable file tree — virtualized (react-window 2.x List) when >50 rows */}
+      {isVirtualized ? (
+        <List
+          listRef={listRef}
+          rowCount={rows.length}
+          rowHeight={rowHeight}
+          rowComponent={VirtualRowItem}
+          rowProps={rowProps}
+          defaultHeight={600}
+          style={{ flex: 1, minHeight: 0 }}
+        />
+      ) : (
+        <div ref={containerRef} className="overflow-y-auto px-4 pb-4">
+          {directoryGroups.map((group) => (
+            <div key={group.directory}>
+              {/* Directory header — collapsible */}
+              {group.directory && (
+                <button
+                  data-testid="dir-header"
+                  className="flex w-full items-center gap-1 text-[10px] font-mono text-muted-foreground/70 mt-2 first:mt-0 px-2 py-0.5 hover:bg-accent/30 transition-colors"
+                  onClick={() => toggleDir(group.directory)}
+                  title={collapsedDirs.has(group.directory) ? "Expand directory" : "Collapse directory"}
+                >
+                  <ChevronRight
+                    className={`h-3 w-3 shrink-0 transition-transform ${collapsedDirs.has(group.directory) ? "" : "rotate-90"}`}
+                  />
+                  <FolderOpen className="h-3 w-3 shrink-0" />
+                  <span className="truncate">{group.directory}</span>
+                </button>
+              )}
+              {/* Files in directory */}
+              {!collapsedDirs.has(group.directory) && (
+                <div className="space-y-0.5">
+                  {group.files.map((file) => {
+                    const fileCommentCount = comments.filter(
+                      (c) => c.filePath === file.newPath && !c.parentCommentId,
+                    ).length;
+                    const isInView = activeFilePaths.has(file.newPath);
+                    const dimmed = selectedCommit && !isInView;
+                    const isViewed = viewedFiles.has(file.newPath);
+                    const dotColor = changeTypeDotColor[file.changeType];
+
+                    return (
+                      <button
+                        key={file.newPath}
+                        data-testid="file-row"
+                        className={`
+                          flex w-full items-center gap-1.5 rounded py-1 text-left text-[11px]
+                          hover:bg-accent/50 transition-colors group
+                          ${group.directory ? "pl-4 pr-2" : "px-2"}
+                          ${dimmed ? "opacity-35" : ""}
+                        `}
+                        onClick={() => onFileClick(file.newPath)}
+                      >
+                        {isViewed ? (
+                          <CheckCircle2 className="h-3 w-3 text-status-success-fg shrink-0" />
+                        ) : (
+                          <FileCode className="h-3 w-3 text-muted-foreground shrink-0" />
+                        )}
+                        {dotColor && (
+                          <span className={`h-1.5 w-1.5 rounded-full shrink-0 ${dotColor}`} />
+                        )}
+                        <span className="truncate flex-1 font-mono">
+                          {getFileName(file.newPath)}
+                        </span>
+                        <span className="flex items-center gap-1 shrink-0">
+                          {fileCommentCount > 0 && (
+                            <span className="flex items-center gap-0.5 text-muted-foreground">
+                              <MessageSquare className="h-2.5 w-2.5" />
+                              {fileCommentCount}
+                            </span>
+                          )}
+                          {file.additions > 0 && (
+                            <span className="text-diff-add-fg text-[10px]">
+                              <Plus className="h-2.5 w-2.5 inline" />
+                              {file.additions}
+                            </span>
+                          )}
+                          {file.deletions > 0 && (
+                            <span className="text-diff-remove-fg text-[10px]">
+                              <Minus className="h-2.5 w-2.5 inline" />
+                              {file.deletions}
+                            </span>
+                          )}
+                        </span>
+                      </button>
+                    );
+                  })}
+                </div>
+              )}
+            </div>
+          ))}
+        </div>
+      )}
     </div>
   );
 }
diff --git a/apps/web/src/components/review/ReviewTab.test.tsx b/apps/web/src/components/review/ReviewTab.test.tsx
new file mode 100644
index 0000000..c7c770a
--- /dev/null
+++ b/apps/web/src/components/review/ReviewTab.test.tsx
@@ -0,0 +1,226 @@
+// @vitest-environment happy-dom
+import "@testing-library/jest-dom/vitest";
+import { render, screen, act } from "@testing-library/react";
+import { vi, describe, it, expect, beforeEach } from "vitest";
+
+// ── Capture props passed to stubs ─────────────────────────────────────────────
+// These are module-level so the vi.mock factories (which are hoisted) can close over them.
+let diffViewerProps: Record<string, unknown> = {};
+let reviewSidebarProps: Record<string, unknown> = {};
+
+vi.mock("./DiffViewer", () => ({
+  DiffViewer: (props: Record<string, unknown>) => {
+    diffViewerProps = props;
+    return <div data-testid="diff-viewer" />;
+  },
+}));
+
+vi.mock("./ReviewSidebar", () => ({
+  ReviewSidebar: (props: Record<string, unknown>) => {
+    reviewSidebarProps = props;
+    return <div data-testid="review-sidebar" />;
+  },
+}));
+
+vi.mock("./ReviewHeader", () => ({
+  ReviewHeader: (props: Record<string, unknown>) => (
+    <div data-testid="review-header">
+      {props.onExpandAll && (
+        <button
+          data-testid="expand-all-btn"
+          onClick={props.onExpandAll as () => void}
+        >
+          Expand all
+        </button>
+      )}
+    </div>
+  ),
+}));
+
+vi.mock("./InitiativeReview", () => ({
+  InitiativeReview: () => <div data-testid="initiative-review" />,
+}));
+
+vi.mock("./comment-index", () => ({
+  buildCommentIndex: vi.fn(() => new Map()),
+}));
+
+vi.mock("sonner", () => ({
+  toast: { success: vi.fn(), error: vi.fn() },
+}));
+
+// ── parseUnifiedDiff spy ───────────────────────────────────────────────────────
+const mockParseUnifiedDiff = vi.fn((_raw: string) => [
+  {
+    oldPath: "a.ts",
+    newPath: "a.ts",
+    status: "modified" as const,
+    additions: 3,
+    deletions: 1,
+    hunks: [],
+  },
+]);
+
+vi.mock("./parse-diff", () => ({
+  get parseUnifiedDiff() {
+    return mockParseUnifiedDiff;
+  },
+}));
+
+// ── tRPC mock factory ─────────────────────────────────────────────────────────
+
+const noopMutation = () => ({
+  mutate: vi.fn(),
+  isPending: false,
+});
+
+const noopQuery = (data: unknown = undefined) => ({
+  data,
+  isLoading: false,
+  isError: false,
+  refetch: vi.fn(),
+});
+
+const mockUtils = {
+  listReviewComments: { invalidate: vi.fn() },
+};
+
+// Server format (FileStatEntry): uses `path` not `newPath`
+const PHASE_FILES = [
+  {
+    path: "a.ts",
+    status: "modified" as const,
+    additions: 5,
+    deletions: 2,
+  },
+];
+
+// trpcMock is a let so tests can override it. The getter in the mock reads the current value.
+let trpcMock = buildTrpcMock();
+
+function buildTrpcMock(overrides: Record<string, unknown> = {}) {
+  return {
+    getInitiative: { useQuery: vi.fn(() => noopQuery({ status: "in_progress" })) },
+    listPhases: {
+      useQuery: vi.fn(() =>
+        noopQuery([{ id: "phase-1", name: "Phase 1", status: "pending_review" }])
+      ),
+    },
+    getInitiativeProjects: { useQuery: vi.fn(() => noopQuery([{ id: "proj-1" }])) },
+    getPhaseReviewDiff: {
+      useQuery: vi.fn(() =>
+        noopQuery({
+          phaseName: "Phase 1",
+          sourceBranch: "cw/phase-1",
+          targetBranch: "main",
+          files: PHASE_FILES,
+          totalAdditions: 5,
+          totalDeletions: 2,
+        })
+      ),
+    },
+    getPhaseReviewCommits: {
+      useQuery: vi.fn(() =>
+        noopQuery({ commits: [], sourceBranch: "cw/phase-1", targetBranch: "main" })
+      ),
+    },
+    getCommitDiff: {
+      useQuery: vi.fn(() => noopQuery({ rawDiff: "" })),
+    },
+    listPreviews: { useQuery: vi.fn(() => noopQuery([])) },
+    getPreviewStatus: { useQuery: vi.fn(() => noopQuery(null)) },
+    listReviewComments: { useQuery: vi.fn(() => noopQuery([])) },
+    startPreview: { useMutation: vi.fn(() => noopMutation()) },
+    stopPreview: { useMutation: vi.fn(() => noopMutation()) },
+    createReviewComment: { useMutation: vi.fn(() => noopMutation()) },
+    resolveReviewComment: { useMutation: vi.fn(() => noopMutation()) },
+    unresolveReviewComment: { useMutation: vi.fn(() => noopMutation()) },
+    replyToReviewComment: { useMutation: vi.fn(() => noopMutation()) },
+    updateReviewComment: { useMutation: vi.fn(() => noopMutation()) },
+    approvePhaseReview: { useMutation: vi.fn(() => noopMutation()) },
+    requestPhaseChanges: { useMutation: vi.fn(() => noopMutation()) },
+    useUtils: vi.fn(() => mockUtils),
+    ...overrides,
+  };
+}
+
+vi.mock("@/lib/trpc", () => ({
+  get trpc() {
+    return trpcMock;
+  },
+}));
+
+// ── Import component after mocks ──────────────────────────────────────────────
+import { ReviewTab } from "./ReviewTab";
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("ReviewTab", () => {
+  beforeEach(() => {
+    diffViewerProps = {};
+    reviewSidebarProps = {};
+    mockParseUnifiedDiff.mockClear();
+    trpcMock = buildTrpcMock();
+  });
+
+  it("1. phase diff loads metadata: DiffViewer receives files array and commitMode=false", () => {
+    render(<ReviewTab initiativeId="init-1" />);
+
+    expect(screen.getByTestId("diff-viewer")).toBeInTheDocument();
+    const files = diffViewerProps.files as unknown[];
+    expect(files).toHaveLength(1);
+    expect(diffViewerProps.commitMode).toBe(false);
+  });
+
+  it("2. no rawDiff parsing in phase mode: parseUnifiedDiff is NOT called", () => {
+    render(<ReviewTab initiativeId="init-1" />);
+
+    expect(mockParseUnifiedDiff).not.toHaveBeenCalled();
+  });
+
+  it("3. commit view parses rawDiff: parseUnifiedDiff called and DiffViewer gets commitMode=true", async () => {
+    trpcMock = buildTrpcMock({
+      getCommitDiff: {
+        useQuery: vi.fn(() =>
+          noopQuery({ rawDiff: "diff --git a/a.ts b/a.ts\nindex 000..111 100644\n--- a/a.ts\n+++ b/a.ts\n@@ -1,1 +1,1 @@\n-old\n+new\n" })
+        ),
+      },
+    });
+
+    render(<ReviewTab initiativeId="init-1" />);
+
+    // Select a commit via the sidebar stub's onSelectCommit prop
+    const { onSelectCommit } = reviewSidebarProps as {
+      onSelectCommit: (hash: string | null) => void;
+    };
+
+    await act(async () => {
+      onSelectCommit("abc123");
+    });
+
+    expect(diffViewerProps.commitMode).toBe(true);
+    expect(mockParseUnifiedDiff).toHaveBeenCalled();
+  });
+
+  it("4. allFiles uses metadata for sidebar: ReviewSidebar receives files from diffQuery.data.files", () => {
+    render(<ReviewTab initiativeId="init-1" />);
+
+    const sidebarFiles = reviewSidebarProps.files as Array<{ newPath: string }>;
+    expect(sidebarFiles).toHaveLength(1);
+    expect(sidebarFiles[0].newPath).toBe("a.ts");
+  });
+
+  it("5. expandAll prop passed: clicking Expand all button causes DiffViewer to receive expandAll=true", async () => {
+    render(<ReviewTab initiativeId="init-1" />);
+
+    // Before clicking, expandAll should be false
+    expect(diffViewerProps.expandAll).toBe(false);
+
+    const expandBtn = screen.getByTestId("expand-all-btn");
+    await act(async () => {
+      expandBtn.click();
+    });
+
+    expect(diffViewerProps.expandAll).toBe(true);
+  });
+});
diff --git a/apps/web/src/components/review/ReviewTab.tsx b/apps/web/src/components/review/ReviewTab.tsx
index 099f380..4e6a2b9 100644
--- a/apps/web/src/components/review/ReviewTab.tsx
+++ b/apps/web/src/components/review/ReviewTab.tsx
@@ -7,7 +7,8 @@ import { DiffViewer } from "./DiffViewer";
 import { ReviewSidebar } from "./ReviewSidebar";
 import { ReviewHeader } from "./ReviewHeader";
 import { InitiativeReview } from "./InitiativeReview";
-import type { ReviewStatus, DiffLine } from "./types";
+import { buildCommentIndex } from "./comment-index";
+import type { ReviewStatus, DiffLine, FileDiff, FileDiffDetail } from "./types";
 
 interface ReviewTabProps {
   initiativeId: string;
@@ -17,6 +18,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
   const [status, setStatus] = useState<ReviewStatus>("pending");
   const [selectedCommit, setSelectedCommit] = useState<string | null>(null);
   const [viewedFiles, setViewedFiles] = useState<Set<string>>(new Set());
+  const [expandAll, setExpandAll] = useState(false);
   const fileRefs = useRef<Map<string, HTMLDivElement>>(new Map());
   const headerRef = useRef<HTMLDivElement>(null);
   const [headerHeight, setHeaderHeight] = useState(0);
@@ -73,7 +75,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
   const projectsQuery = trpc.getInitiativeProjects.useQuery({ initiativeId });
   const firstProjectId = projectsQuery.data?.[0]?.id ?? null;
 
-  // Fetch full branch diff for active phase
+  // Fetch full branch diff for active phase (metadata only, no rawDiff)
   const diffQuery = trpc.getPhaseReviewDiff.useQuery(
     { phaseId: activePhaseId! },
     { enabled: !!activePhaseId && !isInitiativePendingReview },
@@ -95,7 +97,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
   // Preview state
   const previewsQuery = trpc.listPreviews.useQuery({ initiativeId });
   const existingPreview = previewsQuery.data?.find(
-    (p) => p.phaseId === activePhaseId || p.initiativeId === initiativeId,
+    (p: { phaseId?: string; initiativeId?: string }) => p.phaseId === activePhaseId || p.initiativeId === initiativeId,
   );
   const [activePreviewId, setActivePreviewId] = useState<string | null>(null);
   const previewStatusQuery = trpc.getPreviewStatus.useQuery(
@@ -106,12 +108,12 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
   const sourceBranch = diffQuery.data?.sourceBranch ?? commitsQuery.data?.sourceBranch ?? "";
 
   const startPreview = trpc.startPreview.useMutation({
-    onSuccess: (data) => {
+    onSuccess: (data: { id: string; url: string }) => {
       setActivePreviewId(data.id);
       previewsQuery.refetch();
       toast.success(`Preview running at ${data.url}`);
     },
-    onError: (err) => toast.error(`Preview failed: ${err.message}`),
+    onError: (err: { message: string }) => toast.error(`Preview failed: ${err.message}`),
   });
 
   const stopPreview = trpc.stopPreview.useMutation({
@@ -120,7 +122,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
       toast.success("Preview stopped");
       previewsQuery.refetch();
     },
-    onError: (err) => toast.error(`Failed to stop: ${err.message}`),
+    onError: (err: { message: string }) => toast.error(`Failed to stop: ${err.message}`),
   });
 
   const previewState = firstProjectId && sourceBranch
@@ -156,7 +158,17 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
     { enabled: !!activePhaseId && !isInitiativePendingReview },
   );
   const comments = useMemo(() => {
-    return (commentsQuery.data ?? []).map((c) => ({
+    return (commentsQuery.data ?? []).map((c: {
+      id: string;
+      filePath: string;
+      lineNumber: number | null;
+      lineType: string;
+      body: string;
+      author: string;
+      createdAt: string | number;
+      resolved: boolean;
+      parentCommentId?: string | null;
+    }) => ({
       id: c.id,
       filePath: c.filePath,
       lineNumber: c.lineNumber,
@@ -169,11 +181,16 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
     }));
   }, [commentsQuery.data]);
 
+  const commentsByLine = useMemo(
+    () => buildCommentIndex(comments),
+    [comments],
+  );
+
   const createCommentMutation = trpc.createReviewComment.useMutation({
     onSuccess: () => {
       utils.listReviewComments.invalidate({ phaseId: activePhaseId! });
     },
-    onError: (err) => toast.error(`Failed to save comment: ${err.message}`),
+    onError: (err: { message: string }) => toast.error(`Failed to save comment: ${err.message}`),
   });
 
   const resolveCommentMutation = trpc.resolveReviewComment.useMutation({
@@ -192,14 +209,14 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
     onSuccess: () => {
       utils.listReviewComments.invalidate({ phaseId: activePhaseId! });
     },
-    onError: (err) => toast.error(`Failed to post reply: ${err.message}`),
+    onError: (err: { message: string }) => toast.error(`Failed to post reply: ${err.message}`),
   });
 
   const editCommentMutation = trpc.updateReviewComment.useMutation({
     onSuccess: () => {
       utils.listReviewComments.invalidate({ phaseId: activePhaseId! });
     },
-    onError: (err) => toast.error(`Failed to update comment: ${err.message}`),
+    onError: (err: { message: string }) => toast.error(`Failed to update comment: ${err.message}`),
   });
 
   const approveMutation = trpc.approvePhaseReview.useMutation({
@@ -208,23 +225,48 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
       toast.success("Phase approved and merged");
       phasesQuery.refetch();
     },
-    onError: (err) => toast.error(err.message),
+    onError: (err: { message: string }) => toast.error(err.message),
   });
 
-  // Determine which diff to display
-  const activeDiffRaw = selectedCommit
-    ? commitDiffQuery.data?.rawDiff
-    : diffQuery.data?.rawDiff;
+  // Phase branch diff — metadata only, no parsing
+  const phaseFiles: FileDiff[] = useMemo(
+    () => {
+      const serverFiles = diffQuery.data?.files ?? [];
+      // Map server FileStatEntry (path) to frontend FileDiff (newPath)
+      return serverFiles.map((f: {
+        path: string;
+        oldPath?: string;
+        status: FileDiff['status'];
+        additions: number;
+        deletions: number;
+        projectId?: string;
+      }) => ({
+        newPath: f.path,
+        oldPath: f.oldPath ?? f.path,
+        status: f.status,
+        additions: f.additions,
+        deletions: f.deletions,
+        projectId: f.projectId,
+      }));
+    },
+    [diffQuery.data?.files],
+  );
 
-  const files = useMemo(() => {
-    if (!activeDiffRaw) return [];
-    return parseUnifiedDiff(activeDiffRaw);
-  }, [activeDiffRaw]);
+  // Commit diff — still raw, parse client-side
+  const commitFiles: FileDiffDetail[] = useMemo(() => {
+    if (!commitDiffQuery.data?.rawDiff) return [];
+    return parseUnifiedDiff(commitDiffQuery.data.rawDiff);
+  }, [commitDiffQuery.data?.rawDiff]);
 
   const isDiffLoading = selectedCommit
     ? commitDiffQuery.isLoading
     : diffQuery.isLoading;
 
+  // All files for sidebar — always from phase metadata
+  const allFiles = phaseFiles;
+
+  const activeFiles: FileDiff[] | FileDiffDetail[] = selectedCommit ? commitFiles : phaseFiles;
+
   const handleAddComment = useCallback(
     (filePath: string, lineNumber: number, lineType: DiffLine["type"], body: string) => {
       if (!activePhaseId) return;
@@ -267,7 +309,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
       toast.success("Changes requested — revision task dispatched");
       phasesQuery.refetch();
     },
-    onError: (err) => toast.error(err.message),
+    onError: (err: { message: string }) => toast.error(err.message),
   });
 
   const handleRequestChanges = useCallback(() => {
@@ -297,6 +339,11 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
     setSelectedCommit(null);
     setStatus("pending");
     setViewedFiles(new Set());
+    setExpandAll(false);
+  }, []);
+
+  const handleExpandAll = useCallback(() => {
+    setExpandAll(v => !v);
   }, []);
 
   const unresolvedCount = comments.filter((c) => !c.resolved && !c.parentCommentId).length;
@@ -306,12 +353,6 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
     reviewablePhases.find((p) => p.id === activePhaseId)?.name ??
     "Phase";
 
-  // All files from the full branch diff (for sidebar file list)
-  const allFiles = useMemo(() => {
-    if (!diffQuery.data?.rawDiff) return [];
-    return parseUnifiedDiff(diffQuery.data.rawDiff);
-  }, [diffQuery.data?.rawDiff]);
-
   // Initiative-level review takes priority
   if (isInitiativePendingReview) {
     return (
@@ -357,6 +398,9 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
         preview={previewState}
         viewedCount={viewedFiles.size}
         totalCount={allFiles.length}
+        totalAdditions={selectedCommit ? undefined : diffQuery.data?.totalAdditions}
+        totalDeletions={selectedCommit ? undefined : diffQuery.data?.totalDeletions}
+        onExpandAll={handleExpandAll}
       />
 
       {/* Main content area — sidebar always rendered to preserve state */}
@@ -376,7 +420,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
               onFileClick={handleFileClick}
               onCommentClick={handleCommentClick}
               selectedCommit={selectedCommit}
-              activeFiles={files}
+              activeFiles={activeFiles}
               commits={commits}
               onSelectCommit={setSelectedCommit}
               viewedFiles={viewedFiles}
@@ -391,7 +435,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
               <Loader2 className="h-4 w-4 animate-spin" />
               Loading diff...
             </div>
-          ) : files.length === 0 ? (
+          ) : activeFiles.length === 0 ? (
             <div className="flex h-32 items-center justify-center text-muted-foreground text-sm">
               {selectedCommit
                 ? "No changes in this commit"
@@ -399,8 +443,10 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
             </div>
           ) : (
             <DiffViewer
-              files={files}
-              comments={comments}
+              files={activeFiles}
+              phaseId={activePhaseId!}
+              commitMode={!!selectedCommit}
+              commentsByLine={commentsByLine}
               onAddComment={handleAddComment}
               onResolveComment={handleResolveComment}
               onUnresolveComment={handleUnresolveComment}
@@ -409,6 +455,7 @@ export function ReviewTab({ initiativeId }: ReviewTabProps) {
               viewedFiles={viewedFiles}
               onToggleViewed={toggleViewed}
               onRegisterRef={registerFileRef}
+              expandAll={expandAll}
             />
           )}
         </div>
diff --git a/apps/web/src/components/review/comment-index.test.tsx b/apps/web/src/components/review/comment-index.test.tsx
new file mode 100644
index 0000000..c1aafb0
--- /dev/null
+++ b/apps/web/src/components/review/comment-index.test.tsx
@@ -0,0 +1,134 @@
+// @vitest-environment happy-dom
+import "@testing-library/jest-dom/vitest";
+import { render, screen } from "@testing-library/react";
+import { vi, describe, it, expect } from "vitest";
+import { buildCommentIndex } from "./comment-index";
+import type { ReviewComment } from "./types";
+
+// ── Stub CommentThread and CommentForm so LineWithComments renders without deps ──
+vi.mock("./CommentThread", () => ({
+  CommentThread: () => <div data-testid="comment-thread" />,
+}));
+vi.mock("./CommentForm", () => ({
+  CommentForm: vi.fn().mockReturnValue(<div data-testid="comment-form" />),
+}));
+vi.mock("./use-syntax-highlight", () => ({
+  useHighlightedFile: () => null,
+}));
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+function makeComment(overrides: Partial<ReviewComment> & { id: string }): ReviewComment {
+  return {
+    id: overrides.id,
+    filePath: overrides.filePath ?? "src/foo.ts",
+    lineNumber: overrides.lineNumber !== undefined ? overrides.lineNumber : 1,
+    lineType: overrides.lineType ?? "added",
+    body: overrides.body ?? "comment body",
+    author: overrides.author ?? "alice",
+    createdAt: overrides.createdAt ?? "2024-01-01T00:00:00Z",
+    resolved: overrides.resolved ?? false,
+    parentCommentId: overrides.parentCommentId ?? null,
+  };
+}
+
+// ── buildCommentIndex — pure function tests ───────────────────────────────────
+
+describe("buildCommentIndex", () => {
+  it("happy path — basic indexing", () => {
+    const c1 = makeComment({ id: "1", filePath: "src/foo.ts", lineNumber: 10, lineType: "added" });
+    const c2 = makeComment({ id: "2", filePath: "src/bar.ts", lineNumber: 5, lineType: "context" });
+    const map = buildCommentIndex([c1, c2]);
+    expect(map.get("src/foo.ts:10:added")).toEqual([c1]);
+    expect(map.get("src/bar.ts:5:context")).toEqual([c2]);
+    expect(map.size).toBe(2);
+  });
+
+  it("same-line accumulation — two comments land in same array", () => {
+    const c1 = makeComment({ id: "a", filePath: "src/x.ts", lineNumber: 20, lineType: "added" });
+    const c2 = makeComment({ id: "b", filePath: "src/x.ts", lineNumber: 20, lineType: "added" });
+    const map = buildCommentIndex([c1, c2]);
+    expect(map.get("src/x.ts:20:added")).toEqual([c1, c2]);
+    expect(map.size).toBe(1);
+  });
+
+  it("cross-type isolation — same lineNumber but different lineType produces separate entries", () => {
+    const added = makeComment({ id: "a", filePath: "src/x.ts", lineNumber: 10, lineType: "added" });
+    const removed = makeComment({ id: "r", filePath: "src/x.ts", lineNumber: 10, lineType: "removed" });
+    const map = buildCommentIndex([added, removed]);
+    expect(map.get("src/x.ts:10:added")).toEqual([added]);
+    expect(map.get("src/x.ts:10:removed")).toEqual([removed]);
+    expect(map.size).toBe(2);
+  });
+
+  it("null lineNumber — file-level comment stored under filePath:file", () => {
+    const fileComment = makeComment({ id: "f", filePath: "src/z.ts", lineNumber: null, lineType: "context" });
+    const map = buildCommentIndex([fileComment]);
+    expect(map.get("src/z.ts:file")).toEqual([fileComment]);
+  });
+
+  it("empty input — returns empty map", () => {
+    expect(buildCommentIndex([])).toEqual(new Map());
+  });
+});
+
+// ── LineWithComments — component tests ───────────────────────────────────────
+
+import { LineWithComments } from "./LineWithComments";
+import type { DiffLine } from "./types";
+
+const addedLine: DiffLine = {
+  type: "added",
+  content: "const x = 1;",
+  oldLineNumber: null,
+  newLineNumber: 5,
+};
+
+const noop = () => {};
+
+describe("LineWithComments", () => {
+  it("renders comment button with title when lineComments is non-empty", () => {
+    const lineComments = [
+      makeComment({ id: "c1", filePath: "src/foo.ts", lineNumber: 5, lineType: "added" }),
+    ];
+    render(
+      <table>
+        <tbody>
+          <LineWithComments
+            line={addedLine}
+            lineKey={5}
+            lineComments={lineComments}
+            isCommenting={false}
+            onStartComment={noop}
+            onCancelComment={noop}
+            onSubmitComment={noop}
+            onResolveComment={noop}
+            onUnresolveComment={noop}
+          />
+        </tbody>
+      </table>,
+    );
+    expect(screen.getByTitle(/1 comment/)).toBeInTheDocument();
+  });
+
+  it("does not render comment thread row when lineComments is empty", () => {
+    render(
+      <table>
+        <tbody>
+          <LineWithComments
+            line={addedLine}
+            lineKey={5}
+            lineComments={[]}
+            isCommenting={false}
+            onStartComment={noop}
+            onCancelComment={noop}
+            onSubmitComment={noop}
+            onResolveComment={noop}
+            onUnresolveComment={noop}
+          />
+        </tbody>
+      </table>,
+    );
+    expect(document.querySelector("[data-comment-id]")).toBeNull();
+  });
+});
diff --git a/apps/web/src/components/review/comment-index.ts b/apps/web/src/components/review/comment-index.ts
new file mode 100644
index 0000000..cc486ca
--- /dev/null
+++ b/apps/web/src/components/review/comment-index.ts
@@ -0,0 +1,25 @@
+import type { ReviewComment } from "./types";
+
+/**
+ * Build a Map keyed by `"${filePath}:${lineNumber}:${lineType}"` for line-level
+ * comments, or `"${filePath}:file"` for file-level comments (lineNumber === null).
+ *
+ * The compound key (filePath + lineNumber + lineType) is required because
+ * added and removed lines can share the same numeric position in a replacement
+ * hunk (e.g., old line 10 removed, new line 10 added).
+ */
+export function buildCommentIndex(
+  comments: ReviewComment[],
+): Map<string, ReviewComment[]> {
+  const map = new Map<string, ReviewComment[]>();
+  for (const comment of comments) {
+    const key =
+      comment.lineNumber != null
+        ? `${comment.filePath}:${comment.lineNumber}:${comment.lineType}`
+        : `${comment.filePath}:file`;
+    const existing = map.get(key);
+    if (existing) existing.push(comment);
+    else map.set(key, [comment]);
+  }
+  return map;
+}
diff --git a/apps/web/src/components/review/highlight-worker.ts b/apps/web/src/components/review/highlight-worker.ts
new file mode 100644
index 0000000..d663c16
--- /dev/null
+++ b/apps/web/src/components/review/highlight-worker.ts
@@ -0,0 +1,39 @@
+import type { ThemedToken } from 'shiki';
+
+export interface HighlightRequest {
+  id: string;
+  filePath: string;
+  language: string; // resolved lang name (e.g. "typescript") or "text"
+  code: string; // full joined content of new-side lines to highlight
+  lineNumbers: number[]; // new-side line numbers to map tokens back to
+}
+
+export interface HighlightResponse {
+  id: string;
+  tokens: Array<{ lineNumber: number; tokens: ThemedToken[] }>;
+  error?: string;
+}
+
+self.addEventListener('message', async (event: MessageEvent<HighlightRequest>) => {
+  const { id, language, code, lineNumbers } = event.data;
+  try {
+    const { codeToTokens } = await import('shiki');
+    const result = await codeToTokens(code, {
+      lang: language as Parameters<typeof codeToTokens>[1]['lang'],
+      theme: 'github-dark-default',
+    });
+    const tokens: HighlightResponse['tokens'] = result.tokens.map((lineTokens, idx) => ({
+      lineNumber: lineNumbers[idx] ?? idx,
+      tokens: lineTokens,
+    }));
+    const response: HighlightResponse = { id, tokens };
+    self.postMessage(response);
+  } catch (err) {
+    const response: HighlightResponse = {
+      id,
+      tokens: [],
+      error: err instanceof Error ? err.message : String(err),
+    };
+    self.postMessage(response);
+  }
+});
diff --git a/apps/web/src/components/review/parse-diff.ts b/apps/web/src/components/review/parse-diff.ts
index 8a5697e..04d5807 100644
--- a/apps/web/src/components/review/parse-diff.ts
+++ b/apps/web/src/components/review/parse-diff.ts
@@ -1,10 +1,10 @@
-import type { FileDiff, FileChangeType, DiffHunk, DiffLine } from "./types";
+import type { FileDiffDetail, FileDiff, DiffHunk, DiffLine } from "./types";
 
 /**
- * Parse a unified diff string into structured FileDiff objects.
+ * Parse a unified diff string into structured FileDiffDetail objects.
  */
-export function parseUnifiedDiff(raw: string): FileDiff[] {
-  const files: FileDiff[] = [];
+export function parseUnifiedDiff(raw: string): FileDiffDetail[] {
+  const files: FileDiffDetail[] = [];
   const fileChunks = raw.split(/^diff --git /m).filter(Boolean);
 
   for (const chunk of fileChunks) {
@@ -90,19 +90,19 @@ export function parseUnifiedDiff(raw: string): FileDiff[] {
       hunks.push({ header, oldStart, oldCount, newStart, newCount, lines: hunkLines });
     }
 
-    // Derive changeType from header markers and path comparison
-    let changeType: FileChangeType;
+    // Derive status from header markers and path comparison
+    let status: FileDiff['status'];
     if (hasOldDevNull) {
-      changeType = "added";
+      status = "added";
     } else if (hasNewDevNull) {
-      changeType = "deleted";
+      status = "deleted";
     } else if (oldPath !== newPath) {
-      changeType = "renamed";
+      status = "renamed";
     } else {
-      changeType = "modified";
+      status = "modified";
     }
 
-    files.push({ oldPath, newPath, hunks, additions, deletions, changeType });
+    files.push({ oldPath, newPath, hunks, additions, deletions, status });
   }
 
   return files;
diff --git a/apps/web/src/components/review/types.test.ts b/apps/web/src/components/review/types.test.ts
new file mode 100644
index 0000000..8033fd8
--- /dev/null
+++ b/apps/web/src/components/review/types.test.ts
@@ -0,0 +1,29 @@
+// @vitest-environment happy-dom
+import { describe, it, expect } from 'vitest';
+import type { FileDiff, FileDiffDetail } from './types';
+
+describe('FileDiff types', () => {
+  it('FileDiff accepts binary status', () => {
+    const f: FileDiff = {
+      oldPath: 'a.png',
+      newPath: 'a.png',
+      status: 'binary',
+      additions: 0,
+      deletions: 0,
+    };
+    expect(f.status).toBe('binary');
+  });
+
+  it('FileDiffDetail extends FileDiff with hunks', () => {
+    const d: FileDiffDetail = {
+      oldPath: 'a.ts',
+      newPath: 'a.ts',
+      status: 'modified',
+      additions: 5,
+      deletions: 2,
+      hunks: [],
+    };
+    expect(d.hunks).toEqual([]);
+    expect(d.additions).toBe(5);
+  });
+});
diff --git a/apps/web/src/components/review/types.ts b/apps/web/src/components/review/types.ts
index 2b99452..cffdf65 100644
--- a/apps/web/src/components/review/types.ts
+++ b/apps/web/src/components/review/types.ts
@@ -14,21 +14,26 @@ export interface DiffLine {
   newLineNumber: number | null;
 }
 
-export type FileChangeType = 'added' | 'modified' | 'deleted' | 'renamed';
-
+/** Metadata returned by getPhaseReviewDiff — no hunk content */
 export interface FileDiff {
   oldPath: string;
   newPath: string;
-  hunks: DiffHunk[];
+  /** 'binary' is new — prior changeType used FileChangeType which had no 'binary' */
+  status: 'added' | 'modified' | 'deleted' | 'renamed' | 'binary';
   additions: number;
   deletions: number;
-  changeType: FileChangeType;
+  projectId?: string;  // present in multi-project initiatives
+}
+
+/** Full diff with parsed hunks — returned by getFileDiff, parsed client-side */
+export interface FileDiffDetail extends FileDiff {
+  hunks: DiffHunk[];
 }
 
 export interface ReviewComment {
   id: string;
   filePath: string;
-  lineNumber: number; // new-side line number (or old-side for deletions)
+  lineNumber: number | null; // null = file-level comment
   lineType: "added" | "removed" | "context";
   body: string;
   author: string;
diff --git a/apps/web/src/components/review/use-syntax-highlight.fallback.test.ts b/apps/web/src/components/review/use-syntax-highlight.fallback.test.ts
new file mode 100644
index 0000000..d4bc869
--- /dev/null
+++ b/apps/web/src/components/review/use-syntax-highlight.fallback.test.ts
@@ -0,0 +1,131 @@
+// @vitest-environment happy-dom
+// This file tests the chunked main-thread fallback path when Worker
+// construction is blocked (e.g. by CSP). It runs in isolation from the
+// worker-path tests so that module-level state (workersInitialized, workers)
+// starts clean.
+import '@testing-library/jest-dom/vitest'
+import { renderHook, waitFor } from '@testing-library/react'
+import { vi, describe, it, expect, beforeAll, afterAll } from 'vitest'
+
+const MOCK_TOKEN_A = { content: 'const', color: '#569cd6', offset: 0 }
+const MOCK_TOKEN_B = { content: 'x', color: '#9cdcfe', offset: 0 }
+
+// Mock shiki's createHighlighter for the fallback path
+const mockCodeToTokens = vi.fn()
+
+vi.mock('shiki', () => ({
+  createHighlighter: vi.fn().mockResolvedValue({
+    codeToTokens: mockCodeToTokens,
+  }),
+}))
+
+// Stub Worker to throw (simulating CSP) BEFORE the hook module is loaded.
+// initWorkers() catches the exception and leaves workers = [].
+beforeAll(() => {
+  // Use a class so Vitest doesn't warn about constructing vi.fn() without a class impl
+  class BlockedWorker {
+    constructor() {
+      throw new Error('CSP blocks workers')
+    }
+  }
+  vi.stubGlobal('Worker', BlockedWorker)
+
+  mockCodeToTokens.mockReturnValue({
+    tokens: [[MOCK_TOKEN_A], [MOCK_TOKEN_B]],
+  })
+})
+
+afterAll(() => {
+  vi.unstubAllGlobals()
+})
+
+// Dynamic import ensures this file's module instance is fresh (workersInitialized = false).
+// We import inside tests below rather than at the top level.
+
+describe('useHighlightedFile — fallback path (Worker unavailable)', () => {
+  it('falls back to chunked main-thread highlighting when Worker construction throws', async () => {
+    const { useHighlightedFile } = await import('./use-syntax-highlight')
+
+    const lines = [
+      { content: 'const x = 1', newLineNumber: 1, type: 'added' as const },
+      { content: 'let y = 2', newLineNumber: 2, type: 'context' as const },
+    ]
+
+    const { result } = renderHook(() => useHighlightedFile('app.ts', lines))
+
+    // Initially null while chunked highlighting runs
+    expect(result.current).toBeNull()
+
+    // Fallback createHighlighter path eventually resolves tokens
+    await waitFor(
+      () => {
+        expect(result.current).not.toBeNull()
+      },
+      { timeout: 5000 },
+    )
+
+    expect(result.current?.get(1)).toEqual([MOCK_TOKEN_A])
+    expect(result.current?.get(2)).toEqual([MOCK_TOKEN_B])
+  })
+
+  it('returns a complete token map with no lines missing for ≤200-line input (single-chunk equivalence)', async () => {
+    const { useHighlightedFile } = await import('./use-syntax-highlight')
+
+    // 5 lines — well within the 200-line chunk size, so a single codeToTokens call handles all
+    const MOCK_TOKENS = [
+      [{ content: 'line1', color: '#fff', offset: 0 }],
+      [{ content: 'line2', color: '#fff', offset: 0 }],
+      [{ content: 'line3', color: '#fff', offset: 0 }],
+      [{ content: 'line4', color: '#fff', offset: 0 }],
+      [{ content: 'line5', color: '#fff', offset: 0 }],
+    ]
+    mockCodeToTokens.mockReturnValueOnce({ tokens: MOCK_TOKENS })
+
+    const lines = [1, 2, 3, 4, 5].map((n) => ({
+      content: `line${n}`,
+      newLineNumber: n,
+      type: 'context' as const,
+    }))
+
+    const { result } = renderHook(() => useHighlightedFile('src/bar.ts', lines))
+
+    await waitFor(
+      () => {
+        expect(result.current).not.toBeNull()
+      },
+      { timeout: 5000 },
+    )
+
+    // All 5 line numbers must be present — no lines missing
+    expect(result.current!.size).toBe(5)
+    for (let n = 1; n <= 5; n++) {
+      expect(result.current!.get(n)).toEqual(MOCK_TOKENS[n - 1])
+    }
+  })
+
+  it('calls AbortController.abort() when component unmounts during chunked fallback', async () => {
+    const { useHighlightedFile } = await import('./use-syntax-highlight')
+
+    const abortSpy = vi.spyOn(AbortController.prototype, 'abort')
+
+    // Delay the mock so the hook is still in-flight when we unmount
+    mockCodeToTokens.mockImplementationOnce(
+      () =>
+        new Promise((resolve) =>
+          setTimeout(() => resolve({ tokens: [[MOCK_TOKEN_A]] }), 500),
+        ),
+    )
+
+    const lines = [{ content: 'const x = 1', newLineNumber: 1, type: 'added' as const }]
+
+    const { unmount } = renderHook(() => useHighlightedFile('unmount.ts', lines))
+
+    // Unmount while the async chunked highlight is still pending
+    unmount()
+
+    // The cleanup function calls abortController.abort()
+    expect(abortSpy).toHaveBeenCalled()
+
+    abortSpy.mockRestore()
+  })
+})
diff --git a/apps/web/src/components/review/use-syntax-highlight.test.ts b/apps/web/src/components/review/use-syntax-highlight.test.ts
new file mode 100644
index 0000000..1356c3b
--- /dev/null
+++ b/apps/web/src/components/review/use-syntax-highlight.test.ts
@@ -0,0 +1,240 @@
+// @vitest-environment happy-dom
+import '@testing-library/jest-dom/vitest'
+import { renderHook, waitFor, act } from '@testing-library/react'
+import { vi, describe, it, expect, beforeAll, beforeEach, afterAll } from 'vitest'
+
+// ── Worker mock infrastructure ─────────────────────────────────────────────
+//
+// We stub Worker BEFORE importing use-syntax-highlight so that initWorkers()
+// (called from useEffect on first render) picks up our mock.
+// Module-level state (workers, pending, workersInitialized) is shared across
+// all tests in this file — we control behaviour through the mock instances.
+
+type WorkerHandler = (event: { data: unknown }) => void
+
+class MockWorker {
+  static instances: MockWorker[] = []
+
+  messageHandler: WorkerHandler | null = null
+  postMessage = vi.fn()
+
+  constructor() {
+    MockWorker.instances.push(this)
+  }
+
+  addEventListener(type: string, handler: WorkerHandler) {
+    if (type === 'message') this.messageHandler = handler
+  }
+
+  /** Simulate a message arriving from the worker thread */
+  simulateResponse(data: unknown) {
+    this.messageHandler?.({ data })
+  }
+}
+
+// Stub Worker before the hook module is loaded.
+// initWorkers() is lazy (called inside useEffect), so the stub is in place
+// by the time any test renders a hook.
+beforeAll(() => {
+  vi.stubGlobal('Worker', MockWorker)
+})
+
+afterAll(() => {
+  vi.unstubAllGlobals()
+})
+
+beforeEach(() => {
+  // Reset call history between tests; keep instances (pool is created once)
+  MockWorker.instances.forEach((w) => w.postMessage.mockClear())
+})
+
+// Import the hook AFTER the beforeAll stub is registered (hoisted evaluation
+// of the module will not call initWorkers() — that happens in useEffect).
+import { useHighlightedFile } from './use-syntax-highlight'
+
+// ── Helpers ────────────────────────────────────────────────────────────────
+
+const MOCK_TOKEN_A = { content: 'const', color: '#569cd6', offset: 0 }
+const MOCK_TOKEN_B = { content: 'x', color: '#9cdcfe', offset: 0 }
+
+function makeLine(
+  content: string,
+  newLineNumber: number,
+  type: 'added' | 'context' | 'removed' = 'added',
+) {
+  return { content, newLineNumber, type } as const
+}
+
+// ── Tests ──────────────────────────────────────────────────────────────────
+
+describe('useHighlightedFile — worker path', () => {
+  // ── Test 1: Correct message format ───────────────────────────────────────
+
+  it('posts a message to a worker with filePath, language, code, and lineNumbers', async () => {
+    const lines = [
+      makeLine('const x = 1', 1, 'added'),
+      makeLine('const y = 2', 2, 'context'),
+    ]
+
+    renderHook(() => useHighlightedFile('src/index.ts', lines))
+
+    // Wait for initWorkers() to fire and postMessage to be called
+    await waitFor(() => {
+      const totalCalls = MockWorker.instances.reduce(
+        (n, w) => n + w.postMessage.mock.calls.length,
+        0,
+      )
+      expect(totalCalls).toBeGreaterThan(0)
+    })
+
+    // Find which worker received the message
+    const calledWorker = MockWorker.instances.find((w) => w.postMessage.mock.calls.length > 0)
+    expect(calledWorker).toBeDefined()
+    expect(calledWorker!.postMessage).toHaveBeenCalledWith(
+      expect.objectContaining({
+        filePath: 'src/index.ts',
+        language: 'typescript',
+        code: 'const x = 1\nconst y = 2',
+        lineNumbers: [1, 2],
+      }),
+    )
+  })
+
+  // ── Test 2: Response builds token map ─────────────────────────────────────
+
+  it('returns null initially and a LineTokenMap after worker responds', async () => {
+    const lines = [makeLine('const x = 1', 10, 'added')]
+
+    const { result } = renderHook(() => useHighlightedFile('component.ts', lines))
+
+    // Immediately null while worker is pending
+    expect(result.current).toBeNull()
+
+    // Capture the request id from whichever worker received it
+    let requestId = ''
+    let respondingWorker: MockWorker | undefined
+
+    await waitFor(() => {
+      respondingWorker = MockWorker.instances.find((w) => w.postMessage.mock.calls.length > 0)
+      expect(respondingWorker).toBeDefined()
+      requestId = respondingWorker!.postMessage.mock.calls[0][0].id as string
+      expect(requestId).not.toBe('')
+    })
+
+    // Simulate the worker responding
+    act(() => {
+      respondingWorker!.simulateResponse({
+        id: requestId,
+        tokens: [{ lineNumber: 10, tokens: [MOCK_TOKEN_A] }],
+      })
+    })
+
+    await waitFor(() => {
+      expect(result.current).not.toBeNull()
+      expect(result.current?.get(10)).toEqual([MOCK_TOKEN_A])
+    })
+  })
+
+  // ── Test 3: Worker error response → null ──────────────────────────────────
+
+  it('returns null when worker responds with an error field', async () => {
+    const lines = [makeLine('code here', 1, 'added')]
+
+    const { result } = renderHook(() => useHighlightedFile('bad.ts', lines))
+
+    let requestId = ''
+    let respondingWorker: MockWorker | undefined
+
+    await waitFor(() => {
+      respondingWorker = MockWorker.instances.find((w) => w.postMessage.mock.calls.length > 0)
+      expect(respondingWorker).toBeDefined()
+      requestId = respondingWorker!.postMessage.mock.calls[0][0].id as string
+    })
+
+    act(() => {
+      respondingWorker!.simulateResponse({
+        id: requestId,
+        tokens: [],
+        error: 'Worker crashed',
+      })
+    })
+
+    // Error → stays null (plain text fallback in the UI)
+    await new Promise<void>((r) => setTimeout(r, 20))
+    expect(result.current).toBeNull()
+  })
+
+  // ── Test 4: Unmount before response — no state update ────────────────────
+
+  it('silently discards a late worker response after unmount', async () => {
+    const lines = [makeLine('const z = 3', 5, 'added')]
+
+    const { result, unmount } = renderHook(() => useHighlightedFile('late.ts', lines))
+
+    let requestId = ''
+    let respondingWorker: MockWorker | undefined
+
+    await waitFor(() => {
+      respondingWorker = MockWorker.instances.find((w) => w.postMessage.mock.calls.length > 0)
+      expect(respondingWorker).toBeDefined()
+      requestId = respondingWorker!.postMessage.mock.calls[0][0].id as string
+    })
+
+    // Unmount before the response arrives
+    unmount()
+
+    // Simulate the late response — should be silently dropped
+    act(() => {
+      respondingWorker!.simulateResponse({
+        id: requestId,
+        tokens: [{ lineNumber: 5, tokens: [MOCK_TOKEN_B] }],
+      })
+    })
+
+    // result.current is frozen at last rendered value (null) — no update fired
+    expect(result.current).toBeNull()
+  })
+
+  // ── Test 5: Round-robin — two simultaneous requests go to different workers
+
+  it('distributes two simultaneous requests across both pool workers', async () => {
+    // Ensure the pool has been initialised (first test may have done this)
+    // and reset call counts for clean measurement.
+    MockWorker.instances.forEach((w) => w.postMessage.mockClear())
+
+    const lines1 = [makeLine('alpha', 1, 'added')]
+    const lines2 = [makeLine('beta', 1, 'added')]
+
+    // Render two hook instances at the same time
+    renderHook(() => useHighlightedFile('file1.ts', lines1))
+    renderHook(() => useHighlightedFile('file2.ts', lines2))
+
+    await waitFor(() => {
+      const total = MockWorker.instances.reduce((n, w) => n + w.postMessage.mock.calls.length, 0)
+      expect(total).toBe(2)
+    })
+
+    // Both pool workers should each have received exactly one request
+    // (round-robin: even requestCount → workers[0], odd → workers[1])
+    const counts = MockWorker.instances.map((w) => w.postMessage.mock.calls.length)
+    // Pool has 2 workers; each should have received 1 of the 2 requests
+    expect(counts[0]).toBe(1)
+    expect(counts[1]).toBe(1)
+  })
+
+  // ── Test 6: Unknown language → no request ────────────────────────────────
+
+  it('returns null immediately for files with no detectable language', async () => {
+    MockWorker.instances.forEach((w) => w.postMessage.mockClear())
+
+    const lines = [makeLine('raw data', 1, 'added')]
+
+    const { result } = renderHook(() => useHighlightedFile('data.xyz', lines))
+
+    await new Promise<void>((r) => setTimeout(r, 50))
+
+    expect(result.current).toBeNull()
+    const total = MockWorker.instances.reduce((n, w) => n + w.postMessage.mock.calls.length, 0)
+    expect(total).toBe(0)
+  })
+})
diff --git a/apps/web/src/components/review/use-syntax-highlight.ts b/apps/web/src/components/review/use-syntax-highlight.ts
index 673591d..dda0f63 100644
--- a/apps/web/src/components/review/use-syntax-highlight.ts
+++ b/apps/web/src/components/review/use-syntax-highlight.ts
@@ -1,7 +1,59 @@
 import { useState, useEffect, useMemo } from "react";
 import type { ThemedToken } from "shiki";
+import type { HighlightRequest, HighlightResponse } from "./highlight-worker";
 
-/* ── Lazy singleton highlighter ─────────────────────────── */
+/* ── Worker pool (module-level, shared across all hook instances) ─────── */
+
+type PendingResolve = (response: HighlightResponse) => void;
+
+let workers: Worker[] = [];
+let requestCount = 0;
+const MAX_WORKERS = 2;
+const pending = new Map<string, PendingResolve>();
+
+let workersInitialized = false;
+
+function initWorkers(): void {
+  if (workersInitialized) return;
+  workersInitialized = true;
+  try {
+    workers = Array.from({ length: MAX_WORKERS }, () => {
+      const w = new Worker(
+        new URL("./highlight-worker.ts", import.meta.url),
+        { type: "module" },
+      );
+      w.addEventListener("message", (event: MessageEvent<HighlightResponse>) => {
+        const resolve = pending.get(event.data.id);
+        if (resolve) {
+          pending.delete(event.data.id);
+          resolve(event.data);
+        }
+      });
+      return w;
+    });
+  } catch {
+    // CSP or browser compat — fall back to chunked main-thread highlighting
+    workers = [];
+  }
+}
+
+function highlightWithWorker(
+  id: string,
+  language: string,
+  code: string,
+  lineNumbers: number[],
+  filePath: string,
+): Promise<HighlightResponse> {
+  return new Promise<HighlightResponse>((resolve) => {
+    pending.set(id, resolve);
+    const worker = workers[requestCount % MAX_WORKERS];
+    requestCount++;
+    const req: HighlightRequest = { id, filePath, language, code, lineNumbers };
+    worker.postMessage(req);
+  });
+}
+
+/* ── Lazy singleton highlighter (for main-thread fallback) ───────────── */
 
 let highlighterPromise: Promise<Awaited<
   ReturnType<typeof import("shiki")["createHighlighter"]>
@@ -40,10 +92,59 @@ function getHighlighter() {
   return highlighterPromise;
 }
 
-// Pre-warm on module load (non-blocking)
-getHighlighter();
+/* ── Chunked main-thread fallback ────────────────────────────────────── */
 
-/* ── Language detection ──────────────────────────────────── */
+async function highlightChunked(
+  code: string,
+  language: string,
+  lineNumbers: number[],
+  signal: AbortSignal,
+): Promise<LineTokenMap> {
+  const CHUNK = 200;
+  const result: LineTokenMap = new Map();
+  const lines = code.split("\n");
+  const highlighter = await getHighlighter();
+  if (!highlighter) return result;
+
+  for (let i = 0; i < lines.length; i += CHUNK) {
+    if (signal.aborted) break;
+    const chunkLines = lines.slice(i, i + CHUNK);
+    const chunkCode = chunkLines.join("\n");
+    try {
+      const tokenized = highlighter.codeToTokens(chunkCode, {
+        lang: language as Parameters<typeof highlighter.codeToTokens>[1]["lang"],
+        theme: "github-dark-default",
+      });
+      tokenized.tokens.forEach((lineTokens: ThemedToken[], idx: number) => {
+        const lineNum = lineNumbers[i + idx];
+        if (lineNum !== undefined) result.set(lineNum, lineTokens);
+      });
+    } catch {
+      // Skip unparseable chunk
+    }
+
+    // Yield between chunks to avoid blocking the main thread
+    await new Promise<void>((r) => {
+      if (
+        "scheduler" in globalThis &&
+        "yield" in (globalThis as Record<string, unknown>).scheduler
+      ) {
+        (
+          (globalThis as Record<string, unknown>).scheduler as {
+            yield: () => Promise<void>;
+          }
+        )
+          .yield()
+          .then(r);
+      } else {
+        setTimeout(r, 0);
+      }
+    });
+  }
+  return result;
+}
+
+/* ── Language detection ──────────────────────────────────────────────── */
 
 const EXT_TO_LANG: Record<string, string> = {
   ts: "typescript",
@@ -77,7 +178,7 @@ function detectLang(path: string): string | null {
   return EXT_TO_LANG[ext] ?? null;
 }
 
-/* ── Types ───────────────────────────────────────────────── */
+/* ── Types ───────────────────────────────────────────────────────────── */
 
 export type TokenizedLine = ThemedToken[];
 /** Maps newLineNumber → highlighted tokens for that line */
@@ -89,12 +190,23 @@ interface DiffLineInput {
   type: "added" | "removed" | "context";
 }
 
-/* ── Hook ────────────────────────────────────────────────── */
+/* ── Hook ────────────────────────────────────────────────────────────── */
 
 /**
- * Highlights the "new-side" content of a file diff.
- * Returns null until highlighting is ready (progressive enhancement).
- * Only context + added lines are highlighted (removed lines fall back to plain text).
+ * Highlights the "new-side" content of a file diff, returning a map of
+ * line number → syntax tokens.
+ *
+ * Progressive rendering: returns `null` while highlighting is in progress.
+ * Callers (HunkRows → LineWithComments) render plain text when `null` and
+ * patch in highlighted tokens on re-render once the worker or chunked call
+ * resolves.
+ *
+ * Worker path: uses a module-level pool of 2 Web Workers. Round-robin
+ * assignment. Late responses after unmount are silently discarded.
+ *
+ * Fallback path: if Worker construction fails (CSP, browser compat),
+ * falls back to chunked main-thread highlighting via codeToTokens (200
+ * lines/chunk) with scheduler.yield()/setTimeout(0) between chunks.
  */
 export function useHighlightedFile(
   filePath: string,
@@ -129,32 +241,37 @@ export function useHighlightedFile(
       return;
     }
 
-    let cancelled = false;
+    initWorkers(); // no-op after first call
 
-    getHighlighter().then((highlighter) => {
-      if (cancelled || !highlighter) return;
+    const id = crypto.randomUUID();
+    let unmounted = false;
+    const abortController = new AbortController();
 
-      try {
-        const result = highlighter.codeToTokens(code, {
-          lang: lang as Parameters<typeof highlighter.codeToTokens>[1]["lang"],
-          theme: "github-dark-default",
-        });
+    if (workers.length > 0) {
+      highlightWithWorker(id, lang, code, lineNums, filePath).then((response) => {
+        if (unmounted) return; // ignore late responses after unmount
+        if (response.error || response.tokens.length === 0) {
+          setTokenMap(null);
+          return;
+        }
         const map: LineTokenMap = new Map();
-
-        result.tokens.forEach((lineTokens: ThemedToken[], idx: number) => {
-          if (idx < lineNums.length) {
-            map.set(lineNums[idx], lineTokens);
-          }
-        });
-
-        if (!cancelled) setTokenMap(map);
-      } catch {
-        // Language not loaded or parse error — no highlighting
-      }
-    });
+        for (const { lineNumber, tokens } of response.tokens) {
+          map.set(lineNumber, tokens);
+        }
+        setTokenMap(map);
+      });
+    } else {
+      highlightChunked(code, lang, lineNums, abortController.signal).then((map) => {
+        if (unmounted) return;
+        setTokenMap(map.size > 0 ? map : null);
+      });
+    }
 
     return () => {
-      cancelled = true;
+      unmounted = true;
+      abortController.abort();
+      // Remove pending resolver so a late worker response is silently dropped
+      pending.delete(id);
     };
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [cacheKey]);
diff --git a/apps/web/tsconfig.app.tsbuildinfo b/apps/web/tsconfig.app.tsbuildinfo
index 017ab71..de94090 100644
--- a/apps/web/tsconfig.app.tsbuildinfo
+++ b/apps/web/tsconfig.app.tsbuildinfo
@@ -1 +1 @@
-{"root":["./src/app.tsx","./src/main.tsx","./src/routetree.gen.ts","./src/router.tsx","./src/vite-env.d.ts","./src/components/accountcard.tsx","./src/components/actionmenu.tsx","./src/components/addaccountdialog.tsx","./src/components/agentactions.tsx","./src/components/agentdetailspanel.tsx","./src/components/agentoutputviewer.tsx","./src/components/browsertitleupdater.tsx","./src/components/changesetbanner.tsx","./src/components/commandpalette.tsx","./src/components/connectionbanner.tsx","./src/components/createinitiativedialog.tsx","./src/components/decisionlist.tsx","./src/components/dependencychip.tsx","./src/components/dependencyindicator.tsx","./src/components/emptystate.tsx","./src/components/errorboundary.tsx","./src/components/errorstate.tsx","./src/components/executiontab.tsx","./src/components/freetextinput.tsx","./src/components/healthdot.tsx","./src/components/inboxdetailpanel.tsx","./src/components/inboxlist.tsx","./src/components/initiativecard.tsx","./src/components/initiativeheader.tsx","./src/components/initiativelist.tsx","./src/components/keyboardshortcuthint.tsx","./src/components/messagecard.tsx","./src/components/navbadge.tsx","./src/components/optiongroup.tsx","./src/components/phaseaccordion.tsx","./src/components/progressbar.tsx","./src/components/progresspanel.tsx","./src/components/projectpicker.tsx","./src/components/questionform.tsx","./src/components/refinespawndialog.tsx","./src/components/registerprojectdialog.tsx","./src/components/saveindicator.tsx","./src/components/skeleton.tsx","./src/components/skeletoncard.tsx","./src/components/spawnarchitectdropdown.tsx","./src/components/statusbadge.tsx","./src/components/statusdot.tsx","./src/components/taskrow.tsx","./src/components/themetoggle.tsx","./src/components/updatecredentialsdialog.test.tsx","./src/components/updatecredentialsdialog.tsx","./src/components/chat/changesetinline.tsx","./src/components/chat/chatbubble.tsx","./src/components/chat/chatinput.tsx","./src/components/chat/chatslideover.tsx","./src/components/editor/blockdraghandle.tsx","./src/components/editor/blockselectionextension.ts","./src/components/editor/contenttab.tsx","./src/components/editor/deletesubpagedialog.tsx","./src/components/editor/pagebreadcrumb.tsx","./src/components/editor/pagelinkdeletiondetector.ts","./src/components/editor/pagelinkextension.tsx","./src/components/editor/pagetitlecontext.tsx","./src/components/editor/pagetree.tsx","./src/components/editor/phasecontenteditor.tsx","./src/components/editor/refineagentpanel.tsx","./src/components/editor/slashcommandlist.tsx","./src/components/editor/slashcommands.ts","./src/components/editor/tiptapeditor.tsx","./src/components/editor/slash-command-items.ts","./src/components/execution/executioncontext.tsx","./src/components/execution/phaseactions.tsx","./src/components/execution/phasedetailpanel.tsx","./src/components/execution/phasegraph.tsx","./src/components/execution/phasesidebaritem.tsx","./src/components/execution/phasewithtasks.tsx","./src/components/execution/phaseslist.tsx","./src/components/execution/plansection.tsx","./src/components/execution/progresssidebar.tsx","./src/components/execution/taskgraph.tsx","./src/components/execution/taskslideover.tsx","./src/components/execution/index.ts","./src/components/pipeline/pipelinegraph.tsx","./src/components/pipeline/pipelinephasegroup.tsx","./src/components/pipeline/pipelinestagecolumn.tsx","./src/components/pipeline/pipelinetab.tsx","./src/components/pipeline/index.ts","./src/components/review/commentform.tsx","./src/components/review/commentthread.tsx","./src/components/review/conflictresolutionpanel.tsx","./src/components/review/diffviewer.tsx","./src/components/review/filecard.tsx","./src/components/review/hunkrows.tsx","./src/components/review/initiativereview.tsx","./src/components/review/linewithcomments.tsx","./src/components/review/previewcontrols.tsx","./src/components/review/reviewheader.tsx","./src/components/review/reviewsidebar.tsx","./src/components/review/reviewtab.tsx","./src/components/review/dummy-data.ts","./src/components/review/index.ts","./src/components/review/parse-diff.ts","./src/components/review/types.ts","./src/components/review/use-syntax-highlight.ts","./src/components/ui/badge.tsx","./src/components/ui/button.tsx","./src/components/ui/card.tsx","./src/components/ui/dialog.tsx","./src/components/ui/dropdown-menu.tsx","./src/components/ui/input.tsx","./src/components/ui/label.tsx","./src/components/ui/select.tsx","./src/components/ui/sonner.tsx","./src/components/ui/textarea.tsx","./src/components/ui/tooltip.tsx","./src/hooks/index.ts","./src/hooks/useautosave.ts","./src/hooks/usechatsession.ts","./src/hooks/useconflictagent.ts","./src/hooks/useconnectionstatus.ts","./src/hooks/usedebounce.ts","./src/hooks/useglobalkeyboard.ts","./src/hooks/useliveupdates.ts","./src/hooks/useoptimisticmutation.ts","./src/hooks/usephaseautosave.ts","./src/hooks/userefineagent.ts","./src/hooks/usespawnmutation.ts","./src/hooks/usesubscriptionwitherrorhandling.ts","./src/layouts/applayout.tsx","./src/lib/category.ts","./src/lib/invalidation.ts","./src/lib/labels.ts","./src/lib/markdown-to-tiptap.ts","./src/lib/parse-agent-output.ts","./src/lib/theme.tsx","./src/lib/trpc.ts","./src/lib/utils.ts","./src/routes/__root.tsx","./src/routes/agents.tsx","./src/routes/hq.tsx","./src/routes/inbox.tsx","./src/routes/index.tsx","./src/routes/settings.tsx","./src/routes/initiatives/$id.tsx","./src/routes/initiatives/index.tsx","./src/routes/settings/health.tsx","./src/routes/settings/index.tsx","./src/routes/settings/projects.tsx"],"errors":true,"version":"5.9.3"}
\ No newline at end of file
+{"root":["./src/app.tsx","./src/main.tsx","./src/routetree.gen.ts","./src/router.tsx","./src/vite-env.d.ts","./src/components/accountcard.tsx","./src/components/actionmenu.tsx","./src/components/addaccountdialog.tsx","./src/components/agentactions.tsx","./src/components/agentdetailspanel.tsx","./src/components/agentoutputviewer.test.tsx","./src/components/agentoutputviewer.tsx","./src/components/browsertitleupdater.tsx","./src/components/changesetbanner.tsx","./src/components/commandpalette.tsx","./src/components/connectionbanner.tsx","./src/components/createinitiativedialog.tsx","./src/components/decisionlist.tsx","./src/components/dependencychip.tsx","./src/components/dependencyindicator.tsx","./src/components/emptystate.tsx","./src/components/errorboundary.tsx","./src/components/errorstate.tsx","./src/components/executiontab.tsx","./src/components/freetextinput.tsx","./src/components/healthdot.tsx","./src/components/inboxdetailpanel.tsx","./src/components/inboxlist.tsx","./src/components/initiativecard.tsx","./src/components/initiativeheader.tsx","./src/components/initiativelist.tsx","./src/components/keyboardshortcuthint.tsx","./src/components/messagecard.tsx","./src/components/navbadge.tsx","./src/components/optiongroup.tsx","./src/components/phaseaccordion.tsx","./src/components/progressbar.tsx","./src/components/progresspanel.tsx","./src/components/projectpicker.tsx","./src/components/questionform.tsx","./src/components/refinespawndialog.tsx","./src/components/registerprojectdialog.tsx","./src/components/saveindicator.tsx","./src/components/skeleton.tsx","./src/components/skeletoncard.tsx","./src/components/spawnarchitectdropdown.tsx","./src/components/statusbadge.tsx","./src/components/statusdot.tsx","./src/components/taskrow.tsx","./src/components/themetoggle.tsx","./src/components/updatecredentialsdialog.test.tsx","./src/components/updatecredentialsdialog.tsx","./src/components/chat/changesetinline.tsx","./src/components/chat/chatbubble.tsx","./src/components/chat/chatinput.tsx","./src/components/chat/chatslideover.tsx","./src/components/editor/blockdraghandle.tsx","./src/components/editor/blockselectionextension.ts","./src/components/editor/contenttab.tsx","./src/components/editor/deletesubpagedialog.tsx","./src/components/editor/pagebreadcrumb.tsx","./src/components/editor/pagelinkdeletiondetector.ts","./src/components/editor/pagelinkextension.tsx","./src/components/editor/pagetitlecontext.tsx","./src/components/editor/pagetree.tsx","./src/components/editor/phasecontenteditor.tsx","./src/components/editor/refineagentpanel.tsx","./src/components/editor/slashcommandlist.tsx","./src/components/editor/slashcommands.ts","./src/components/editor/tiptapeditor.tsx","./src/components/editor/slash-command-items.ts","./src/components/execution/executioncontext.tsx","./src/components/execution/phaseactions.tsx","./src/components/execution/phasedetailpanel.tsx","./src/components/execution/phasegraph.tsx","./src/components/execution/phasesidebaritem.tsx","./src/components/execution/phasewithtasks.tsx","./src/components/execution/phaseslist.tsx","./src/components/execution/plansection.tsx","./src/components/execution/progresssidebar.tsx","./src/components/execution/taskgraph.tsx","./src/components/execution/taskslideover.tsx","./src/components/execution/index.ts","./src/components/hq/hqblockedsection.tsx","./src/components/hq/hqemptystate.tsx","./src/components/hq/hqneedsapprovalsection.tsx","./src/components/hq/hqneedsreviewsection.tsx","./src/components/hq/hqsections.test.tsx","./src/components/hq/hqwaitingforinputsection.tsx","./src/components/hq/types.ts","./src/components/pipeline/pipelinegraph.tsx","./src/components/pipeline/pipelinephasegroup.tsx","./src/components/pipeline/pipelinestagecolumn.tsx","./src/components/pipeline/pipelinetab.tsx","./src/components/pipeline/index.ts","./src/components/review/commentform.tsx","./src/components/review/commentthread.tsx","./src/components/review/conflictresolutionpanel.tsx","./src/components/review/diffviewer.tsx","./src/components/review/filecard.tsx","./src/components/review/hunkrows.tsx","./src/components/review/initiativereview.tsx","./src/components/review/linewithcomments.tsx","./src/components/review/previewcontrols.tsx","./src/components/review/reviewheader.tsx","./src/components/review/reviewsidebar.test.tsx","./src/components/review/reviewsidebar.tsx","./src/components/review/reviewtab.tsx","./src/components/review/dummy-data.ts","./src/components/review/index.ts","./src/components/review/parse-diff.ts","./src/components/review/types.ts","./src/components/review/use-syntax-highlight.ts","./src/components/ui/badge.tsx","./src/components/ui/button.tsx","./src/components/ui/card.tsx","./src/components/ui/dialog.tsx","./src/components/ui/dropdown-menu.tsx","./src/components/ui/input.tsx","./src/components/ui/label.tsx","./src/components/ui/select.tsx","./src/components/ui/skeleton.tsx","./src/components/ui/sonner.tsx","./src/components/ui/textarea.tsx","./src/components/ui/tooltip.tsx","./src/hooks/index.ts","./src/hooks/useautosave.ts","./src/hooks/usechatsession.ts","./src/hooks/useconflictagent.ts","./src/hooks/useconnectionstatus.ts","./src/hooks/usedebounce.ts","./src/hooks/useglobalkeyboard.ts","./src/hooks/useliveupdates.ts","./src/hooks/useoptimisticmutation.ts","./src/hooks/usephaseautosave.ts","./src/hooks/userefineagent.ts","./src/hooks/usespawnmutation.ts","./src/hooks/usesubscriptionwitherrorhandling.ts","./src/layouts/applayout.tsx","./src/lib/category.ts","./src/lib/invalidation.ts","./src/lib/labels.ts","./src/lib/markdown-to-tiptap.ts","./src/lib/parse-agent-output.test.ts","./src/lib/parse-agent-output.ts","./src/lib/theme.tsx","./src/lib/trpc.ts","./src/lib/utils.ts","./src/routes/__root.tsx","./src/routes/agents.tsx","./src/routes/hq.test.tsx","./src/routes/hq.tsx","./src/routes/inbox.tsx","./src/routes/index.tsx","./src/routes/settings.tsx","./src/routes/initiatives/$id.tsx","./src/routes/initiatives/index.tsx","./src/routes/settings/health.tsx","./src/routes/settings/index.tsx","./src/routes/settings/projects.tsx"],"errors":true,"version":"5.9.3"}
\ No newline at end of file
diff --git a/apps/web/vite.config.ts b/apps/web/vite.config.ts
index 2dee645..69aca80 100644
--- a/apps/web/vite.config.ts
+++ b/apps/web/vite.config.ts
@@ -16,6 +16,11 @@ export default defineConfig({
       "@": path.resolve(__dirname, "./src"),
     },
   },
+  worker: {
+    // ES module workers are required when the app uses code-splitting (Rollup
+    // can't bundle IIFE workers alongside dynamic imports).
+    format: "es",
+  },
   server: {
     watch: {
       ignored: ['**/routeTree.gen.ts'],
diff --git a/docs/frontend.md b/docs/frontend.md
index eee8f3d..b8f3e2e 100644
--- a/docs/frontend.md
+++ b/docs/frontend.md
@@ -14,6 +14,7 @@
 | Tiptap | Rich text editor (ProseMirror-based) |
 | Lucide | Icon library |
 | Geist Sans/Mono | Typography (variable fonts in `public/fonts/`) |
+| react-window 2.x | Virtualized list rendering for large file trees in ReviewSidebar |
 
 ## Design System (v2)
 
@@ -114,15 +115,26 @@ The initiative detail page has three tabs managed via local state (not URL param
 ### Review Components (`src/components/review/`)
 | Component | Purpose |
 |-----------|---------|
-| `ReviewTab` | Review tab container — orchestrates header, diff, sidebar, and preview. Phase-level review has threaded inline comments (with reply support) + Request Changes; initiative-level review has Request Changes (summary prompt) + Push Branch / Merge & Push |
-| `ReviewHeader` | Consolidated toolbar: phase selector pills, branch info, stats, preview controls, approve/reject actions |
-| `ReviewSidebar` | VSCode-style icon strip (Files/Commits views) with file list, root-only comment counts, and commit navigation |
-| `DiffViewer` | Unified diff renderer with threaded inline comments (root + reply threads) |
+| `ReviewTab` | Review tab container — orchestrates header, diff, sidebar, and preview. Phase-level review has threaded inline comments (with reply support) + Request Changes; initiative-level review has Request Changes (summary prompt) + Push Branch / Merge & Push. Phase diff uses metadata-only `FileDiff[]` from `getPhaseReviewDiff`; commit diff parses `rawDiff` via `parseUnifiedDiff` → `FileDiffDetail[]`. Passes `commitMode`, `phaseId`, `expandAll` to DiffViewer |
+| `ReviewHeader` | Consolidated toolbar: phase selector pills, branch info, stats (uses `totalAdditions`/`totalDeletions` props when available, falls back to summing files), preview controls, Expand all button, approve/reject actions |
+| `ReviewSidebar` | VSCode-style icon strip (Files/Commits views) with file list, root-only comment counts, and commit navigation. FilesView uses react-window 2.x `List` for virtualized rendering when the row count exceeds 50 (dir-headers + file rows). Scroll position is preserved across Files ↔ Commits tab switches. Directories are collapsible. Clicking a file scrolls the virtual list to that row. |
+| `DiffViewer` | Unified diff renderer with threaded inline comments (root + reply threads). Accepts `FileDiff[] | FileDiffDetail[]`, `phaseId`, `commitMode`, `expandAll` props |
 | `CommentThread` | Renders root comment with resolve/reopen + nested reply threads (agent replies styled with primary border). Inline reply form |
 | `ConflictResolutionPanel` | Merge conflict detection + agent resolution in initiative review. Shows conflict files, spawns conflict agent, inline questions, re-check on completion |
 | `PreviewPanel` | Docker preview status: building/running/failed with start/stop (legacy, now integrated into ReviewHeader) |
 | `ProposalCard` | Individual proposal display |
 
+#### Syntax Highlighting (`use-syntax-highlight.ts` + `highlight-worker.ts`)
+
+`useHighlightedFile(filePath, allLines)` returns `LineTokenMap | null`. Tokenisation runs off the main thread:
+
+- **Worker path** (default): a module-level pool of 2 ES module Web Workers (`highlight-worker.ts`) each import shiki's `codeToTokens` dynamically. Requests are round-robined by `requestCount % 2`. Responses are correlated by UUID. Late responses after unmount are silently discarded via the `pending` Map.
+- **Fallback path** (CSP / browser-compat): if `Worker` construction throws, `createHighlighter` is used on the main thread but processes 200 lines per chunk, yielding between chunks via `scheduler.yield()` or `setTimeout(0)`.
+
+Callers receive `null` while highlighting is in progress and a populated `Map<lineNumber, ThemedToken[]>` once it resolves. `LineWithComments` already renders plain text when `null`, so no caller changes are needed.
+
+Vite must be configured with `worker.format: 'es'` (added to `vite.config.ts`) for the worker chunk to bundle correctly alongside code-split app chunks.
+
 ### UI Primitives (`src/components/ui/`)
 shadcn/ui components: badge (6 status variants + xs size), button, card, dialog, dropdown-menu, input, label, select, sonner, textarea, tooltip.
 
diff --git a/docs/git-process-logging.md b/docs/git-process-logging.md
index 2e5d8c4..16968af 100644
--- a/docs/git-process-logging.md
+++ b/docs/git-process-logging.md
@@ -40,6 +40,8 @@ Worktrees stored in `.cw-worktrees/` subdirectory of the repo. Each agent gets a
 | `ensureBranch(repoPath, branch, baseBranch)` | Create branch from base if it doesn't exist (idempotent) |
 | `mergeBranch(repoPath, source, target)` | Merge via ephemeral worktree, returns conflict info |
 | `diffBranches(repoPath, base, head)` | Three-dot diff between branches |
+| `diffBranchesStat(repoPath, base, head)` | Per-file metadata (path, status, additions, deletions) — no hunk content. Binary files included with `status: 'binary'` and counts of 0. Returns `FileStatEntry[]`. |
+| `diffFileSingle(repoPath, base, head, filePath)` | Raw unified diff for a single file (three-dot diff). `filePath` must be URL-decoded. Returns empty string for binary files. |
 | `deleteBranch(repoPath, branch)` | Delete local branch (no-op if missing) |
 | `branchExists(repoPath, branch)` | Check local branches |
 | `remoteBranchExists(repoPath, branch)` | Check remote tracking branches (`origin/<branch>`) |
diff --git a/docs/server-api.md b/docs/server-api.md
index cd2f17a..7ac57ab 100644
--- a/docs/server-api.md
+++ b/docs/server-api.md
@@ -122,7 +122,8 @@ Each procedure uses `require*Repository(ctx)` helpers that throw `TRPCError(INTE
 | listInitiativePhaseDependencies | query | All dependency edges |
 | getPhaseDependencies | query | What this phase depends on |
 | getPhaseDependents | query | What depends on this phase |
-| getPhaseReviewDiff | query | Full branch diff for pending_review phase |
+| getPhaseReviewDiff | query | File-level metadata for pending_review phase: `{phaseName, sourceBranch, targetBranch, files: FileStatEntry[], totalAdditions, totalDeletions}` — no hunk content. Results are cached in-memory by `phaseId:headHash` (TTL: `REVIEW_DIFF_CACHE_TTL_MS`, default 5 min). Cache is invalidated when a task merges into the phase branch. |
+| getFileDiff | query | Per-file unified diff on demand: `{phaseId, filePath, projectId?}` → `{binary: boolean, rawDiff: string}`; `filePath` must be URL-encoded; binary files return `{binary: true, rawDiff: ''}` |
 | getPhaseReviewCommits | query | List commits between initiative and phase branch |
 | getCommitDiff | query | Diff for a single commit (by hash) in a phase |
 | approvePhaseReview | mutation | Approve and merge phase branch |
diff --git a/package-lock.json b/package-lock.json
index 89c8514..ab9b297 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -73,12 +73,14 @@
         "@tiptap/suggestion": "^3.19.0",
         "@trpc/client": "^11.9.0",
         "@trpc/react-query": "^11.9.0",
+        "@types/react-window": "^1.8.8",
         "class-variance-authority": "^0.7.1",
         "clsx": "^2.1.1",
         "geist": "^1.7.0",
         "lucide-react": "^0.563.0",
         "react": "^19.0.0",
         "react-dom": "^19.0.0",
+        "react-window": "^2.2.7",
         "sonner": "^2.0.7",
         "tailwind-merge": "^3.4.0",
         "tippy.js": "^6.3.7"
@@ -5198,6 +5200,15 @@
         "@types/react": "^19.2.0"
       }
     },
+    "node_modules/@types/react-window": {
+      "version": "1.8.8",
+      "resolved": "https://registry.npmjs.org/@types/react-window/-/react-window-1.8.8.tgz",
+      "integrity": "sha512-8Ls660bHR1AUA2kuRvVG9D/4XpRC6wjAaPT9dil7Ckc76eP9TKWZwwmgfq8Q1LANX3QNDnoU4Zp48A3w+zK69Q==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/react": "*"
+      }
+    },
     "node_modules/@types/unist": {
       "version": "3.0.3",
       "resolved": "https://registry.npmjs.org/@types/unist/-/unist-3.0.3.tgz",
@@ -9131,6 +9142,16 @@
         }
       }
     },
+    "node_modules/react-window": {
+      "version": "2.2.7",
+      "resolved": "https://registry.npmjs.org/react-window/-/react-window-2.2.7.tgz",
+      "integrity": "sha512-SH5nvfUQwGHYyriDUAOt7wfPsfG9Qxd6OdzQxl5oQ4dsSsUicqQvjV7dR+NqZ4coY0fUn3w1jnC5PwzIUWEg5w==",
+      "license": "MIT",
+      "peerDependencies": {
+        "react": "^18.0.0 || ^19.0.0",
+        "react-dom": "^18.0.0 || ^19.0.0"
+      }
+    },
     "node_modules/read-cache": {
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/read-cache/-/read-cache-1.0.0.tgz",
diff --git a/vitest.config.ts b/vitest.config.ts
index fcfefaf..4c6a261 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -5,11 +5,24 @@ import path from 'node:path';
 export default defineConfig({
   plugins: [react()],
   resolve: {
+    // Alias react to the parent monorepo's copy, matching what @testing-library
+    // loads react-dom from. This ensures React DOM and our components share the
+    // same ReactSharedInternals and hook dispatcher — preventing null-dispatcher
+    // errors when running tests from a git worktree.
     alias: {
       '@': path.resolve(__dirname, './apps/web/src'),
+      react: path.resolve(__dirname, '../../../../node_modules/react'),
+      'react-dom': path.resolve(__dirname, '../../../../node_modules/react-dom'),
     },
+    dedupe: ['react', 'react-dom'],
   },
   test: {
+    // Force react-dom and @testing-library through Vite's module graph so that
+    // the resolve.alias for 'react-dom' applies (prevents parent-monorepo
+    // react-dom loading a different React instance than our source files).
+    deps: {
+      inline: ['react-dom', '@testing-library/react'],
+    },
     // Enable test globals (describe, it, expect without imports)
     globals: true,
     env: {