fix: Persist and expose task dependencies from detail output

Detail agents define task dependencies in YAML frontmatter but they were
silently dropped — never written to the task_dependencies table. This
caused all tasks to dispatch in parallel regardless of intended ordering,
and the frontend showed no dependency information.

- Add fileIdToDbId mapping and second-pass dependency creation in
  output-handler.ts (mirrors existing phase dependency pattern)
- Add task_dependency to changeset entry entityType enum
- Add listPhaseTaskDependencies tRPC procedure for batch querying
- Wire blockedBy in PhaseDetailPanel and PhaseWithTasks from real data
- Clarify dependency semantics in detail prompt

apps/server/agent/output-handler.ts

@@ -498,6 +498,7 @@ export class OutputHandler {
           const phaseInput = readFrontmatterFile(join(agentWorkdir, '.cw', 'input', 'phase.md'));
           const phaseId = (phaseInput?.data?.id as string) ?? null;
           const entries: CreateChangeSetEntryData[] = [];
+          const fileIdToDbId = new Map<string, string>();
 
           // Load existing tasks for dedup — prevents duplicates when multiple agents finish concurrently
           const existingTasks = phaseId ? await this.taskRepository.findByPhaseId(phaseId) : [];
@@ -506,6 +507,9 @@ export class OutputHandler {
           for (const [i, t] of tasks.entries()) {
             if (existingNames.has(t.title)) {
               log.info({ agentId, task: t.title, phaseId }, 'skipped duplicate task');
+              // Map deduped file ID to existing DB ID for dependency resolution
+              const existing = existingTasks.find(et => et.name === t.title);
+              if (existing) fileIdToDbId.set(t.id, existing.id);
               continue;
             }
             try {
@@ -518,6 +522,7 @@ export class OutputHandler {
                 category: (t.category as any) ?? 'execute',
                 type: (t.type as any) ?? 'auto',
               });
+              fileIdToDbId.set(t.id, created.id);
               existingNames.add(t.title); // prevent dupes within same agent output
               entries.push({
                 entityType: 'task',
@@ -536,6 +541,29 @@ export class OutputHandler {
             }
           }
 
+          // Second pass: create task dependencies
+          let depSortOrder = entries.length;
+          for (const t of tasks) {
+            const taskDbId = fileIdToDbId.get(t.id);
+            if (!taskDbId || t.dependencies.length === 0) continue;
+            for (const depFileId of t.dependencies) {
+              const depDbId = fileIdToDbId.get(depFileId);
+              if (!depDbId) continue;
+              try {
+                await this.taskRepository.createDependency(taskDbId, depDbId);
+                entries.push({
+                  entityType: 'task_dependency',
+                  entityId: `${taskDbId}:${depDbId}`,
+                  action: 'create',
+                  newState: JSON.stringify({ taskId: taskDbId, dependsOnTaskId: depDbId }),
+                  sortOrder: depSortOrder++,
+                });
+              } catch (err) {
+                log.warn({ agentId, taskDbId, depFileId, err: err instanceof Error ? err.message : String(err) }, 'failed to create task dependency');
+              }
+            }
+          }
+
           if (entries.length > 0) {
             try {
               const cs = await this.changeSetRepository!.createWithEntries({

apps/server/agent/prompts/detail.ts

@@ -13,7 +13,7 @@ ${CODEBASE_EXPLORATION}
 
 <output_format>
 Write one file per task to \`.cw/output/tasks/{id}.md\`:
-- Frontmatter: \`title\`, \`category\` (execute|research|discuss|plan|detail|refine|verify|merge|review), \`type\` (auto|checkpoint:human-verify|checkpoint:decision|checkpoint:human-action), \`dependencies\` (list of task IDs)
+- Frontmatter: \`title\`, \`category\` (execute|research|discuss|plan|detail|refine|verify|merge|review), \`type\` (auto|checkpoint:human-verify|checkpoint:decision|checkpoint:human-action), \`dependencies\` (list of task IDs that must complete before this task can start)
 - Body: Detailed task description
 </output_format>
 
@@ -59,6 +59,7 @@ Parallel tasks must not modify the same files. Include a file list per task:
 Files: src/db/schema/users.ts (create), src/db/migrations/001_users.sql (create)
 \`\`\`
 If two tasks touch the same file or one needs the other's output, add a dependency.
+Tasks with no dependencies run in parallel. Add a dependency when one task needs another's output or modifies the same files.
 </file_ownership>
 
 <task_sizing>