Implement Milestone

## Implementation Plan: M{X}.{Y} — {Title}

### Deliverables
- [ ] {deliverable 1}
- [ ] {deliverable 2}
…

### File Plan
|File                  |Action|Purpose|
|----------------------|------|-------|
|`packages/.../file.ts`|Create|…      |
|`packages/.../file.ts`|Modify|…      |

### Dependencies Needed
- {package}: {reason}

### Open Questions
- {anything unclear that needs developer input}

### Estimated Agent Tasks
- {number} files to create
- {number} files to modify
- {number} test files

Present this plan and wait for approval before proceeding.

Phase 3: Implementation

Execute the plan. For each deliverable:

1. Create/modify files following project conventions from CLAUDE.md
2. Write tests alongside implementation (not after)
3. Run tests after each logical unit: bun --filter {package} test
4. Run typecheck periodically: bun --filter {package} typecheck
5. Commit message format: feat(M{X}.{Y}): {description}

Delegation Rules

• Backend work → delegate to @backend agent
• Agent runtime work → delegate to @agent-runtime agent
• Mobile work → delegate to @mobile agent
• Shared types/schemas → handle directly (affects all packages)
• Cross-cutting concerns → handle directly, coordinate between agents

Quality Checks

After implementation:

• All tests pass: bun test
• Type checks clean: bun typecheck
• Lint clean: bun lint
• No hardcoded secrets or API keys
• Error handling on all external calls (DB, API, file I/O)
• Structured logging on key operations

Phase 4: Milestone Review

After implementation is complete, invoke the /milestone-review skill to update the build plan.

Error Recovery

If you encounter a blocker:

1. Document it in the implementation plan
2. Check if a workaround exists
3. If the blocker is external (API access, infra setup), mark the milestone as 🚧 and note what's needed
4. Move on to the next milestone that doesn't depend on this one