docs(02-01): complete SQLite database setup plan

Tasks completed: 3/3
- Install Drizzle ORM and SQLite dependencies
- Create database connection factory
- Define task hierarchy schema

SUMMARY: .planning/phases/02-data-layer/02-01-SUMMARY.md

.planning/phases/02-data-layer/02-01-SUMMARY.md

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+---
+phase: 02-data-layer
+plan: 01
+subsystem: database
+tags: [drizzle, sqlite, better-sqlite3, orm, schema]
+
+# Dependency graph
+requires:
+  - phase: 01
+    provides: Core infrastructure (CLI, server, process management)
+provides:
+  - SQLite database connection factory
+  - Task hierarchy schema (initiative -> phase -> plan -> task)
+  - Drizzle ORM types for all entities
+  - Task dependency relationship table
+affects: [03-git-integration, 04-agent-lifecycle, 05-task-dispatch]
+
+# Tech tracking
+tech-stack:
+  added: [drizzle-orm, better-sqlite3, drizzle-kit]
+  patterns: [factory-function-not-singleton, wal-mode, foreign-key-cascades]
+
+key-files:
+  created:
+    - src/db/config.ts
+    - src/db/index.ts
+    - src/db/schema.ts
+    - drizzle.config.ts
+  modified:
+    - package.json
+
+key-decisions:
+  - "Factory function (not singleton) for database - allows isolated test instances"
+  - "WAL mode enabled for better concurrent read performance"
+  - "Foreign keys enabled with cascade deletes for data integrity"
+  - "Unix timestamps (integers) for SQLite compatibility"
+  - "Separate task_dependencies table for many-to-many task relationships"
+
+patterns-established:
+  - "Database factory: createDatabase(path?) returns isolated instance"
+  - "Schema organization: tables + relations + types in schema.ts"
+  - "Environment override: CW_DB_PATH for testing with :memory:"
+
+# Metrics
+duration: 3min
+completed: 2026-01-30
+---
+
+# Phase 2 Plan 1: SQLite Database Setup Summary
+
+**SQLite database with Drizzle ORM and four-level task hierarchy schema (initiative -> phase -> plan -> task)**
+
+## Performance
+
+- **Duration:** 3 min
+- **Started:** 2026-01-30T13:22:12Z
+- **Completed:** 2026-01-30T13:24:59Z
+- **Tasks:** 3
+- **Files modified:** 5
+
+## Accomplishments
+
+- Installed Drizzle ORM with better-sqlite3 driver for synchronous SQLite operations
+- Created database connection factory with WAL mode and foreign key enforcement
+- Defined complete task hierarchy schema with proper cascade delete relationships
+- Exported TypeScript types for all entities (Initiative, Phase, Plan, Task, TaskDependency)
+- Configured drizzle-kit for future migration support
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Install Drizzle ORM and SQLite dependencies** - `caf8bb0` (chore)
+2. **Task 2: Create database connection factory** - `d7e4649` (feat)
+3. **Task 3: Define task hierarchy schema** - `b492f64` (feat)
+
+## Files Created/Modified
+
+- `src/db/config.ts` - Database path resolution with CW_DB_PATH override
+- `src/db/index.ts` - createDatabase() factory function with WAL mode
+- `src/db/schema.ts` - Complete schema with 5 tables and relations
+- `drizzle.config.ts` - Drizzle Kit configuration for migrations
+- `package.json` - Added drizzle-orm, better-sqlite3, drizzle-kit dependencies
+
+## Decisions Made
+
+- **Factory over singleton:** createDatabase() returns new instance each call, enabling isolated test databases
+- **WAL mode:** Enabled for better concurrent read performance in local-first app
+- **Foreign keys on:** SQLite has FK disabled by default, enabled for data integrity
+- **Unix timestamps:** Used integer timestamps for SQLite compatibility vs Date objects
+- **Separate dependencies table:** task_dependencies junction table instead of JSON array for proper relational queries
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None.
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+
+- Database foundation complete for repository layer implementation
+- Schema ready for CRUD operations in Phase 2 Plan 2
+- Types exported for use throughout codebase
+- No blockers for continuing
+
+---
+*Phase: 02-data-layer*
+*Completed: 2026-01-30*