docs(12-03): complete agent manager decompose mode plan

Tasks completed: 3/3
- Task 3: Extend AgentStoppedEvent reason type (dependency)
- Task 1: Update ClaudeAgentManager for decompose mode
- Task 2: Update MockAgentManager for decompose mode

SUMMARY: .planning/phases/12-phase-task-decomposition/12-03-SUMMARY.md

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

@@ -0,0 +1,103 @@
+---
+phase: 12-phase-task-decomposition
+plan: 03
+subsystem: agent
+tags: [agent-mode, json-schema, mock-manager, typescript, decompose]
+
+# Dependency graph
+requires:
+  - phase: 12-phase-task-decomposition
+    plan: 01
+    provides: decomposeOutputSchema, decomposeOutputJsonSchema, TaskBreakdown type
+provides:
+  - Mode-aware agent spawning handles 'decompose' mode with decomposeOutputJsonSchema
+  - ClaudeAgentManager.handleDecomposeOutput() method for decompose completion handling
+  - MockAgentManager supports decompose_complete scenarios for E2E testing
+  - AgentStoppedEvent.reason extended with 'decompose_complete'
+affects: [12-05, 12-08]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "Decompose mode follows same handler dispatch pattern as discuss/breakdown modes"
+    - "MockAgentScenario discriminated union extended for all four agent modes"
+
+key-files:
+  created: []
+  modified:
+    - src/agent/manager.ts
+    - src/agent/mock-manager.ts
+    - src/events/types.ts
+
+key-decisions:
+  - "Task 3 executed first as Tasks 1-2 depend on AgentStoppedEvent reason type"
+  - "handleDecomposeOutput follows exact pattern of handleBreakdownOutput for consistency"
+
+patterns-established:
+  - "Mode handler extension: new modes add handler method + switch case + JSON schema mapping"
+
+# Metrics
+duration: 7min
+completed: 2026-02-01
+---
+
+# Phase 12 Plan 03: Agent Manager Decompose Mode Summary
+
+**Updated ClaudeAgentManager and MockAgentManager to support decompose mode with decomposeOutputJsonSchema for phase-to-task decomposition**
+
+## Performance
+
+- **Duration:** 7 min
+- **Started:** 2026-02-01T10:38:18Z
+- **Completed:** 2026-02-01T10:45:07Z
+- **Tasks:** 3
+- **Files modified:** 3
+
+## Accomplishments
+
+- Extended AgentStoppedEvent.reason type with 'decompose_complete' for event typing
+- Added decompose mode support to ClaudeAgentManager (schema selection, handler method, switch routing)
+- Added decompose_complete scenario support to MockAgentManager for E2E testing
+- All 402 tests pass with no regressions
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 3: Extend AgentStoppedEvent reason type** - `fe3fed0` (feat) - executed first as dependency
+2. **Task 1: Update ClaudeAgentManager for decompose mode** - `8754cde` (feat)
+3. **Task 2: Update MockAgentManager for decompose mode** - `2bd0bc5` (feat)
+
+## Files Created/Modified
+
+- `src/events/types.ts` - Added 'decompose_complete' to AgentStoppedEvent reason union
+- `src/agent/manager.ts` - Added decompose imports, getJsonSchemaForMode case, handleDecomposeOutput method, switch case routing
+- `src/agent/mock-manager.ts` - Added TaskBreakdown import, decompose_complete scenario type, completeAgent handler case
+
+## Decisions Made
+
+1. **12-03: Task execution order** - Task 3 (AgentStoppedEvent) executed first since Tasks 1-2 depend on 'decompose_complete' reason type
+2. **12-03: Handler pattern consistency** - handleDecomposeOutput follows exact structure of handleBreakdownOutput for maintainability
+
+## Deviations from Plan
+
+None - plan executed exactly as written. Task order adjusted for dependency correctness.
+
+## Issues Encountered
+
+None
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+
+- Decompose mode fully supported in both agent managers
+- Ready for 12-04 (Plan tRPC Procedures) and 12-05 (Decompose tRPC Procedures)
+- MockAgentManager can simulate decompose_complete scenarios for E2E testing in 12-08
+
+---
+*Phase: 12-phase-task-decomposition*
+*Completed: 2026-02-01*