feat: Add threaded review comments + agent comment responses

Introduces GitHub-style threaded comments via parentCommentId self-reference.
Users and agents can reply within comment threads, and review agents receive
comment IDs so they can post targeted responses via comment-responses.json.

- Migration 0032: parentCommentId column + index on review_comments
- Repository: createReply() copies parent context, default author 'you' → 'user'
- tRPC: replyToReviewComment procedure, requestPhaseChanges passes threaded comments
- Orchestrator: formats [comment:ID] tags with full reply threads in task description
- Agent IO: readCommentResponses() reads .cw/output/comment-responses.json
- OutputHandler: processes agent comment responses (creates replies, resolves threads)
- Execute prompt: conditional <review_comments> block when task has [comment:] markers
- Frontend: CommentThread renders root+replies with agent-specific styling + reply form
- Sidebar/ReviewTab: root-only comment counts, reply mutation plumbing through DiffViewer chain

apps/server/db/repositories/drizzle/review-comment.ts

@@ -23,7 +23,43 @@ export class DrizzleReviewCommentRepository implements ReviewCommentRepository {
       lineNumber: data.lineNumber,
       lineType: data.lineType,
       body: data.body,
-      author: data.author ?? 'you',
+      author: data.author ?? 'user',
+      parentCommentId: data.parentCommentId ?? null,
+      resolved: false,
+      createdAt: now,
+      updatedAt: now,
+    });
+    const rows = await this.db
+      .select()
+      .from(reviewComments)
+      .where(eq(reviewComments.id, id))
+      .limit(1);
+    return rows[0]!;
+  }
+
+  async createReply(parentCommentId: string, body: string, author?: string): Promise<ReviewComment> {
+    // Fetch parent comment to copy context fields
+    const parentRows = await this.db
+      .select()
+      .from(reviewComments)
+      .where(eq(reviewComments.id, parentCommentId))
+      .limit(1);
+    const parent = parentRows[0];
+    if (!parent) {
+      throw new Error(`Parent comment not found: ${parentCommentId}`);
+    }
+
+    const now = new Date();
+    const id = nanoid();
+    await this.db.insert(reviewComments).values({
+      id,
+      phaseId: parent.phaseId,
+      filePath: parent.filePath,
+      lineNumber: parent.lineNumber,
+      lineType: parent.lineType,
+      body,
+      author: author ?? 'user',
+      parentCommentId,
       resolved: false,
       createdAt: now,
       updatedAt: now,

apps/server/db/repositories/review-comment-repository.ts

@@ -13,10 +13,12 @@ export interface CreateReviewCommentData {
   lineType: 'added' | 'removed' | 'context';
   body: string;
   author?: string;
+  parentCommentId?: string;  // for replies
 }
 
 export interface ReviewCommentRepository {
   create(data: CreateReviewCommentData): Promise<ReviewComment>;
+  createReply(parentCommentId: string, body: string, author?: string): Promise<ReviewComment>;
   findByPhaseId(phaseId: string): Promise<ReviewComment[]>;
   resolve(id: string): Promise<ReviewComment | null>;
   unresolve(id: string): Promise<ReviewComment | null>;

apps/server/db/schema.ts

@@ -617,11 +617,13 @@ export const reviewComments = sqliteTable('review_comments', {
   lineType: text('line_type', { enum: ['added', 'removed', 'context'] }).notNull(),
   body: text('body').notNull(),
   author: text('author').notNull().default('you'),
+  parentCommentId: text('parent_comment_id').references((): ReturnType<typeof text> => reviewComments.id, { onDelete: 'cascade' }),
   resolved: integer('resolved', { mode: 'boolean' }).notNull().default(false),
   createdAt: integer('created_at', { mode: 'timestamp' }).notNull(),
   updatedAt: integer('updated_at', { mode: 'timestamp' }).notNull(),
 }, (table) => [
   index('review_comments_phase_id_idx').on(table.phaseId),
+  index('review_comments_parent_id_idx').on(table.parentCommentId),
 ]);
 
 export type ReviewComment = InferSelectModel<typeof reviewComments>;