Agent Skills: Implementation Phase

Implementation Phase

Execute the implementation plan for: $ARGUMENTS

Purpose

Implementation executes an approved plan with discipline and verification. The goal is not just working code, but verified, documented progress that matches the plan. Implementation follows the plan strictly, verifying each step before proceeding.

Process

1. Locate the Plan

If $ARGUMENTS is a file path (starts with / or docs/ or ends with .md):

• Read the file at that path directly
• Check if plan is marked approved
• Proceed based on stakes level

Otherwise, search for plan by topic:

Look for plan at: docs/plans/YYYY-MM-DD-<topic>-plan.md

(Search for files matching *-<topic>-plan.md pattern using $ARGUMENTS as the topic)

If plan exists:

• Read the plan document
• Check if plan is marked approved
• Proceed based on stakes level

If no plan exists:

• Check stakes level of the requested work
• Apply enforcement based on stakes

2. Apply Stakes-Based Enforcement

High Stakes (architectural, security-sensitive, hard to rollback):

Cannot proceed without an approved plan.

High-stakes implementations require:
1. Research phase (rpikit:researching-codebase skill)
2. Approved plan (rpikit:writing-plans skill)

Invoke the Skill tool with skill "rpikit:writing-plans" to create a plan first.

Stop and do not proceed.

Medium Stakes (multiple files, moderate impact):

Warning: No approved plan found for '$ARGUMENTS'.

Medium-stakes changes benefit from planning.

Use AskUserQuestion with options:

• "Create a plan first" (recommended)
• "Proceed with caution"
• "Cancel"

Low Stakes (isolated, easy rollback):

Note: Consider rpikit:researching-codebase and rpikit:writing-plans skills for better results.
Proceeding with implementation...

Proceed with inline planning.

3. Offer Worktree Isolation

Before making changes, offer to create an isolated worktree.

First, check if already in a worktree:

# Check if .git is a file (indicates additional worktree, not main repo)
test -f .git

Run this command via the Bash tool:

• Exit code 0 (success): .git is a file → already in a worktree → skip the prompt and proceed to progress tracking
• Exit code 1 (failure): .git is a directory → main repository → continue with the worktree offer below

If not in a worktree, offer based on stakes level:

High Stakes:

Use AskUserQuestion with options:

• "Use worktree (Recommended)" - Create isolated workspace for safer changes
• "Continue in current directory" - Proceed without isolation

Medium Stakes:

Use AskUserQuestion with options:

• "Use worktree" - Create isolated workspace
• "Continue in current directory" - Proceed without isolation

Low Stakes:

Brief mention only:

Tip: For isolation, use EnterWorktree.
Proceeding in current directory...

Skip the prompt and continue.

If user chooses worktree:

Use EnterWorktree to create the isolated workspace. Implementation continues in the new worktree directory.

When implementation is complete, use ExitWorktree with action: "keep" to preserve the branch and return to the main working directory.

If implementation is aborted (user cancels at a checkpoint or verification fails beyond recovery), use ExitWorktree with action: "discard" to clean up the worktree without preserving changes.

Caution: EnterWorktree has known active bugs — bypassPermissions may be ineffective (#29110) and background agents may not have pwd set correctly (#27749). Always verify the working directory after entering a worktree.

4. Initialize Progress Tracking

Create tasks from plan steps using TaskCreate:

Read each step from the plan and create a corresponding task:

• Use step descriptions as the task subject (imperative form)
• Include the step's action and verify criteria in the task description
• Set activeForm to a present-continuous description (e.g., "Implementing auth middleware")
• All tasks start as pending
• Use addBlockedBy via TaskUpdate when plan steps have sequential requirements (e.g., Step 1.2 depends on Step 1.1)

5. Execute Steps in Order

For each step in the plan:

1. Mark in_progress - Update task via TaskUpdate

2. Locate target files - If file path is unclear or missing, use file-finder:

   Task tool with subagent_type: "file-finder"
   Prompt: "Find [what the step describes]. Need to [action from plan]"
   

3. Read target files - Always read before modifying

4. Make the change - Follow plan specification exactly

5. Run verification - Execute the verify criteria

6. Confirm success - Only proceed if verification passes

7. Mark completed - Update task via TaskUpdate immediately

8. Update plan - Mark step complete in plan document

6. Checkpoint After Phases

After completing each phase:

Summarize progress:

Phase [N] complete:
- Step N.1: [description]
- Step N.2: [description]
- Step N.3: [description]

Verifications: All passed

Use AskUserQuestion:

• "Continue to Phase [N+1]"
• "Review changes so far"
• "Pause implementation"

7. Handle Failures

When verification fails:

1. Stop - Do not proceed to next step

2. Report - Explain what failed and why

3. Diagnose - Investigate the cause. If the error involves external libraries or unfamiliar issues, use web-researcher:

   Task tool with subagent_type: "web-researcher"
   Prompt: "[error message or issue] in [library/context]"
   

4. Propose fix - Suggest correction based on diagnosis

If fix requires plan changes:

Verification failed for Step [X.Y]: [description]

The planned approach doesn't work because: [reason]

Proposed adjustment: [new approach]

Use AskUserQuestion:

• "Approve adjustment and continue"
• "Return to planning"
• "Cancel implementation"

8. Complete Implementation

When all steps are done:

1. Mark all tasks completed via TaskUpdate

2. Update plan document status section

3. Run final verification (full test suite if applicable)

4. Run code review:

   Task tool with subagent_type: "code-reviewer"
   Prompt: "Review implementation changes for: $ARGUMENTS"
   

   If verdict is REQUEST CHANGES (soft gate):

   Use AskUserQuestion:

   • "Address findings first" (recommended)
   • "Proceed anyway"
   • "Cancel implementation"

   If user chooses "Proceed anyway", continue to security review.

5. Run security review:

   Task tool with subagent_type: "security-reviewer"
   Prompt: "Review implementation changes for: $ARGUMENTS"
   

   If verdict is FAIL, stop and address findings before completing.

6. Summarize results

Implementation complete for '$ARGUMENTS'.

Summary:
- Steps completed: [N]
- Phases completed: [M]
- Files changed: [list]
- Tests: [pass/fail status]

Plan updated: docs/plans/YYYY-MM-DD-<topic>-plan.md

All success criteria met.

Core Principles

Follow the Plan

The plan is the contract. Deviations require explicit approval:

• Execute steps in order
• Use specified files and approaches
• Meet verification criteria before proceeding
• Document any necessary deviations

Verify Before Claiming Done

Never claim completion without evidence:

• Run the verification for each step
• Confirm tests pass
• Check that changes match expectations
• Document verification results

Track Progress Visibly

Use TaskCreate / TaskUpdate / TaskList for real-time progress:

• Create tasks from plan steps via TaskCreate
• Mark in_progress via TaskUpdate when starting
• Mark completed via TaskUpdate only after verification
• Use TaskList to review overall progress
• Update plan document with status

Progress Documentation

Task-Based Tracking

Maintain real-time visibility using structured tasks:

TaskCreate: subject="Add validation function", status=pending
TaskCreate: subject="Update API endpoint", status=pending
TaskUpdate: taskId=1, status=in_progress
TaskUpdate: taskId=1, status=completed
TaskList → shows current state of all tasks

Plan Document Updates

Update the plan file as implementation progresses:

#### Step 1.1: Add validation function

- **Status**: Complete
- **Verified**: Unit tests pass
- **Notes**: Used existing regex pattern from validatePhone()

Test-Driven Execution

When plan includes test steps, follow TDD:

1. Red - Write failing test first
2. Green - Write minimal code to pass
3. Refactor - Improve without breaking

Mark test steps complete only when tests pass.

Deviation Handling

If implementation reveals the plan needs changes:

1. Stop current step

2. Document the issue

3. If additional files are needed, use file-finder to locate them:

   Task tool with subagent_type: "file-finder"
   Prompt: "Find files related to [issue discovered]. Need to [proposed change]"
   

4. Propose plan modification with updated file references

5. Get approval before continuing

Never deviate silently from the approved plan.

Verification Techniques

Code Verification

For code changes, verify by:

• Syntax check: Code compiles/parses without errors
• Type check: TypeScript/type annotations pass
• Lint check: No new linting errors
• Unit tests: Related tests pass

Behavior Verification

For functionality, verify by:

• Manual test: Exercise the feature
• Integration test: Run relevant integration tests
• API test: Hit endpoints and verify responses
• UI check: Visual verification if applicable

Regression Verification

Ensure no breakage:

• Full test suite: Run all tests
• Build: Project builds successfully
• Smoke test: Core functionality works

Anti-Patterns to Avoid

Skipping Verification

Wrong: Marking done without running verification Right: Always run verification, document results

Proceeding After Failure

Wrong: Moving to next step when current step failed Right: Stop, diagnose, fix, re-verify

Deviating Silently

Wrong: Changing approach without updating plan Right: Request approval for plan changes

Batch Completion

Wrong: Marking multiple steps done at once Right: Mark complete immediately after each verification

Ignoring Stakes

Wrong: Rushing high-stakes changes Right: Respect enforcement based on stakes level

Quality Checklist

During implementation:

• [ ] Always read files before modifying
• [ ] Run verification after each step
• [ ] Mark tasks completed immediately (no batching)
• [ ] Update plan document with status
• [ ] Get approval at phase checkpoints
• [ ] Document any deviations

At completion:

• [ ] All plan steps marked done
• [ ] All verifications passed
• [ ] Code review completed (code-reviewer agent)
• [ ] Security review completed (security-reviewer agent)
• [ ] Plan document updated with completion status
• [ ] Final summary provided