implement_plan

<workflow_contract>

1. Follow all 4 steps in order.
2. Read the implementation plan fully before doing any code changes.
3. Use todowrite in Step 1 to create granular implementation and verification todos.
4. Keep exactly one todo in_progress at a time and mark items complete immediately after finishing them.
5. Do not skip verification; each phase must be implemented, verified, and reflected on before advancing.
6. If the codebase materially diverges from plan expectations, stop, document the mismatch, and ask the user before proceeding.
7. When resuming partial work, trust completed checkmarks and prior artifacts unless current files clearly contradict them. </workflow_contract>

MAKE SURE you follow ALL 4 steps in order. Step 1 loads context and creates your detailed todo list. Steps 2-4 form the implementation loop: implement phase → verify and reflect → iterate.

<step_1>

Step 1: Load Plan Context and Build the Todo List

1. Parse the implementation plan path from <userMessage>.
2. If no plan path was provided, ask the user for the implementation plan path and stop.
3. Read the implementation plan fully. If it does not exist, report that clearly and stop.
4. If the plan filename ends with _implementation.md, read the sibling {pair_base}_requirements.md. Warn if it is missing, but continue.
5. Call tools_thoughts_list_documents filtered to artifact documents and look for prior handoff or progress artifacts whose filenames start with plan_{basename}_.
6. Read any matching artifacts so you understand completed work, past decisions, and resume context.
7. Read all files explicitly referenced in the implementation plan before editing them.
8. Parse the plan into granular todos. For each phase, create:
   • one todo per significant implementation change
   • one verification todo for that phase's success criteria
9. If the plan already contains completed checkmarks or the artifacts show prior completion, reflect that in the initial todo state unless the current code clearly contradicts it.

Good example todos

• Phase 1: Add rate_limit.rs middleware file — New file with RateLimiter struct and middleware fn
• Phase 1: Update router.rs to use rate limiter — Import and wrap routes
• Phase 1: Add RATE_LIMIT_RPS config key — Add to config.rs with default 100
• Verify Phase 1 — Run cargo test rate_limit, check middleware applies to /api routes
• Phase 2: Add Redis backend for rate limiting — Add redis client, update RateLimiter

Bad example todos

• Phase 1
• Do the implementation
• Run tests

</step_1>

<step_2>