docs(12): create phase plan

Phase 12: Phase-Task Decomposition
- 8 plans in 4 waves
- 4 parallel, 4 sequential
- Ready for execution

.planning/phases/12-phase-task-decomposition/12-03-PLAN.md

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+---
+phase: 12-phase-task-decomposition
+plan: 03
+type: execute
+wave: 2
+depends_on: ["12-01"]
+files_modified:
+  - src/agent/manager.ts
+  - src/agent/mock-manager.ts
+autonomous: true
+---
+
+<objective>
+Update ClaudeAgentManager and MockAgentManager to support decompose mode.
+
+Purpose: Enable spawning agents in decompose mode with the correct JSON schema. Agents in this mode break phases into tasks.
+
+Output: Mode-aware agent spawning handles 'decompose' mode with decomposeOutputJsonSchema.
+</objective>
+
+<execution_context>
+@~/.claude/get-shit-done/workflows/execute-plan.md
+@~/.claude/get-shit-done/templates/summary.md
+</execution_context>
+
+<context>
+@.planning/PROJECT.md
+@.planning/ROADMAP.md
+@.planning/STATE.md
+
+# Depends on Plan 01 for decompose schema
+@.planning/phases/12-phase-task-decomposition/12-01-SUMMARY.md
+
+# Pattern reference from Phase 11 (mode handling)
+@.planning/phases/11-architect-agent/11-03-SUMMARY.md
+
+# Source files to modify
+@src/agent/manager.ts
+@src/agent/schema.ts
+</context>
+
+<tasks>
+
+<task type="auto">
+  <name>Task 1: Update ClaudeAgentManager for decompose mode</name>
+  <files>src/agent/manager.ts</files>
+  <action>
+1. Import decomposeOutputSchema and decomposeOutputJsonSchema from schema.ts
+
+2. Update getJsonSchemaForMode() to handle 'decompose':
+   ```typescript
+   case 'decompose':
+     return decomposeOutputJsonSchema;
+   ```
+
+3. Add handleDecomposeOutput() method following pattern of handleBreakdownOutput():
+   - Parse output with decomposeOutputSchema
+   - Handle 'decompose_complete' status → emit agent:stopped with reason: 'decompose_complete'
+   - Handle 'questions' status → emit agent:stopped with reason: 'questions'
+   - Handle 'unrecoverable_error' → emit agent:stopped with reason: 'error'
+
+4. Update handleAgentCompletion() switch to call handleDecomposeOutput for mode: 'decompose'
+  </action>
+  <verify>npm run build passes</verify>
+  <done>ClaudeAgentManager handles decompose mode with correct schema and completion handling</done>
+</task>
+
+<task type="auto">
+  <name>Task 2: Update MockAgentManager for decompose mode</name>
+  <files>src/agent/mock-manager.ts</files>
+  <action>
+1. Add 'decompose_complete' to MockAgentScenario status type (alongside 'context_complete' and 'breakdown_complete')
+
+2. Add tasks field to scenario result type for decompose_complete:
+   ```typescript
+   tasks?: Array<{ number: number; name: string; description: string; type: string; dependencies: number[] }>;
+   ```
+
+3. Update handleAgentCompletion() to handle decompose scenarios:
+   - If status is 'decompose_complete', emit agent:stopped with reason: 'decompose_complete'
+   - Include tasks in the output event if present
+
+4. Update resume() to handle decompose mode similarly to breakdown mode
+  </action>
+  <verify>npm run build passes, npm test passes</verify>
+  <done>MockAgentManager handles decompose mode scenarios for E2E testing</done>
+</task>
+
+<task type="auto">
+  <name>Task 3: Extend AgentStoppedEvent reason type</name>
+  <files>src/events/types.ts</files>
+  <action>
+Update AgentStoppedEvent reason type to include 'decompose_complete':
+
+```typescript
+reason: 'completed' | 'stopped' | 'error' | 'questions' | 'context_complete' | 'breakdown_complete' | 'decompose_complete';
+```
+
+This follows the pattern established in Phase 11 for context_complete and breakdown_complete.
+  </action>
+  <verify>npm run build passes</verify>
+  <done>AgentStoppedEvent reason includes 'decompose_complete'</done>
+</task>
+
+</tasks>
+
+<verification>
+Before declaring plan complete:
+- [ ] npm run build succeeds
+- [ ] npm test passes all tests
+- [ ] ClaudeAgentManager.getJsonSchemaForMode returns decomposeOutputJsonSchema for 'decompose'
+- [ ] ClaudeAgentManager.handleDecomposeOutput exists and handles all statuses
+- [ ] MockAgentManager handles decompose_complete scenarios
+- [ ] AgentStoppedEvent.reason includes 'decompose_complete'
+</verification>
+
+<success_criteria>
+- All tasks completed
+- All verification checks pass
+- No errors or warnings introduced
+- Decompose mode fully supported in both managers
+</success_criteria>
+
+<output>
+After completion, create `.planning/phases/12-phase-task-decomposition/12-03-SUMMARY.md`
+</output>