docs(12-02): complete PlanRepository extensions plan

Tasks completed: 3/3
- Extend PlanRepository port interface
- Implement methods in DrizzlePlanRepository
- Export types from repositories index (already done)

SUMMARY: .planning/phases/12-phase-task-decomposition/12-02-SUMMARY.md

.planning/phases/12-phase-task-decomposition/12-02-SUMMARY.md

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+---
+phase: 12-phase-task-decomposition
+plan: 02
+subsystem: database
+tags: [drizzle, repository, hexagonal, ports-adapters]
+
+# Dependency graph
+requires:
+  - phase: 02-data-layer
+    provides: Repository pattern, Drizzle ORM setup
+  - phase: 11-architect-agent
+    provides: Pattern reference for repository extensions
+provides:
+  - PlanRepository.findByPhaseId method (already existed)
+  - PlanRepository.getNextNumber method
+affects: [12-phase-task-decomposition, decompose-agent]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - Aggregate queries with drizzle max() for sequence generation
+
+key-files:
+  created: []
+  modified:
+    - src/db/repositories/plan-repository.ts
+    - src/db/repositories/drizzle/plan.ts
+
+key-decisions:
+  - "getNextNumber uses max() aggregate, returning 1 if no plans exist (same pattern as PhaseRepository)"
+  - "findByPhaseId already existed - only getNextNumber was new"
+
+# Metrics
+duration: 2min
+completed: 2026-02-01
+---
+
+# Phase 12 Plan 02: Extend PlanRepository Summary
+
+**Extended PlanRepository with getNextNumber method for plan sequence generation in decomposition workflow**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-02-01T10:30:00Z
+- **Completed:** 2026-02-01T10:32:19Z
+- **Tasks:** 3
+- **Files modified:** 2
+
+## Accomplishments
+
+- Added `getNextNumber` method to PlanRepository interface for getting next available plan number
+- Implemented `getNextNumber` in DrizzlePlanRepository using max() aggregate query
+- Verified all existing types already properly exported from repositories index
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Extend PlanRepository port interface** - `0044fbf` (feat)
+2. **Task 2: Implement methods in DrizzlePlanRepository** - `3187e2a` (feat)
+3. **Task 3: Export types from repositories index** - No commit needed (types already exported)
+
+## Files Created/Modified
+
+- `src/db/repositories/plan-repository.ts` - Added getNextNumber method signature
+- `src/db/repositories/drizzle/plan.ts` - Implemented getNextNumber with max() query
+
+## Decisions Made
+
+1. **getNextNumber uses max() aggregate** - Returns MAX(number) + 1, or 1 if no plans exist for phase (same pattern as DrizzlePhaseRepository)
+2. **findByPhaseId already existed** - Plan mentioned adding it but it was already in the interface and implemented
+
+## Deviations from Plan
+
+### Auto-fixed Issues
+
+**1. [Scope Adjustment] findByPhaseId already existed**
+- **Found during:** Task 1 (interface extension)
+- **Issue:** Plan specified adding findByPhaseId but it already existed in both interface and adapter
+- **Resolution:** Only added getNextNumber as that was the only missing method
+- **Impact:** None - plan outcome achieved
+
+**Total deviations:** 1 (scope adjustment - findByPhaseId already present)
+**Impact on plan:** No negative impact - result matches plan intent
+
+## Issues Encountered
+
+None - all methods implemented successfully, all 402 tests pass.
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+
+- PlanRepository now has all methods needed for decompose agent workflow
+- findByPhaseId: Get all plans for a phase
+- getNextNumber: Get next available plan number for sequence generation
+- Ready for 12-03-PLAN.md (tRPC procedures for task decomposition)
+
+---
+*Phase: 12-phase-task-decomposition*
+*Completed: 2026-02-01*