Kild lane: you are running inside a kild room, in a workspace (worktree + branch) the kild engine assigned. The driver owns isolation and publishing — SKIP any step below that creates or switches branches or worktrees, pulls or rebases the base branch, pushes, opens PRs, or moves/archives plan artifacts, and never run gh pr checkout. Your job ends at implement → validate → commit in the current workspace, reporting evidence. Where a step spawns subagents, do that analysis inline — or ask the room's orchestrator to invite a helper agent.

Arguments: $ARGUMENTS (and $1, $2, ...) refer to the arguments given when this skill was invoked. Take them from the user's request; if absent, infer them from the conversation.

Implement Plan

Plan: $ARGUMENTS

Your Mission

Execute the plan end-to-end with rigorous self-validation. You are autonomous.

Core Philosophy: Validation loops catch mistakes early. Run checks after every change. Fix issues immediately. The goal is a working implementation, not just code that exists.

Golden Rule: If a validation fails, fix it before moving on. Never accumulate broken state.

Phase 0: DETECT - Project Environment

0.1 Identify Package Manager

Check for these files to determine the project's toolchain:

Store the detected runner - use it for all subsequent commands.

0.2 Detect Base Branch

Determine the base branch for branching and syncing:

1. Check arguments: If $ARGUMENTS contains --base <branch>, extract that value and remove the flag from the plan path argument
2. Auto-detect from remote:

   git symbolic-ref refs/remotes/origin/HEAD 2>/dev/null | sed 's@^refs/remotes/origin/@@'

3. Fallback if detection fails:

   git remote show origin 2>/dev/null | grep 'HEAD branch' | awk '{print $NF}'

4. Last resort: main

Store as {base-branch} — use this value for ALL branch comparisons, rebasing, and syncing. Never hardcode main or master.

0.3 Identify Validation Scripts

Check package.json (or equivalent) for available scripts:

• Type checking: type-check, typecheck, tsc
• Linting: lint, lint:fix
• Testing: test, test:unit, test:integration
• Building: build, compile

Use the plan's "Validation Commands" section - it should specify exact commands for this project.

Phase 1: LOAD - Read the Plan

1.1 Load Plan File

cat $ARGUMENTS

1.2 Extract Key Sections

Locate and understand:

• Summary - What we're building
• Patterns to Mirror - Code to copy from
• Files to Change - CREATE/UPDATE list
• Step-by-Step Tasks - Implementation order
• Validation Commands - How to verify (USE THESE, not hardcoded commands)
• Acceptance Criteria - Definition of done

1.3 Validate Plan Exists

If plan not found:

Error: Plan not found at $ARGUMENTS

Create a plan first: the prp-plan skill "feature description"

PHASE_1_CHECKPOINT:

• Plan file loaded
• Key sections identified
• Tasks list extracted

Phase 2: PREPARE - Git State

2.1 Check Current State

git branch --show-current
git status --porcelain
git worktree list

2.2 Branch Decision

2.3 Sync with Remote

git fetch origin
git pull --rebase origin {base-branch} 2>/dev/null || true

PHASE_2_CHECKPOINT:

• On correct branch (not {base-branch} with uncommitted work)
• Working directory ready
• Up to date with remote

Phase 3: EXECUTE - Implement Tasks

For each task in the plan's Step-by-Step Tasks section:

3.1 Read Context

1. Read the MIRROR file reference from the task
2. Understand the pattern to follow
3. Read any IMPORTS specified

3.2 Implement

1. Make the change exactly as specified
2. Follow the pattern from MIRROR reference
3. Handle any GOTCHA warnings

3.3 Validate Immediately

After EVERY file change, run the type-check command from the plan's Validation Commands section.

Common patterns:

• {runner} run type-check (JS/TS projects)
• mypy . (Python)
• cargo check (Rust)
• go build ./... (Go)

If types fail:

1. Read the error
2. Fix the issue
3. Re-run type-check
4. Only proceed when passing

3.4 Track Progress

Log each task as you complete it:

Task 1: CREATE src/features/x/models.ts ✅
Task 2: CREATE src/features/x/service.ts ✅
Task 3: UPDATE src/routes/index.ts ✅

Update the plan's status markers as you go (newer templates use [ ] / [wip] / [x] / [f]): set a task to [wip] when you start it and [x] when its validation passes — or [f] if it cannot be made to pass (record why in the plan's Agent Notes and continue). Save the plan file after each change so progress survives an interruption. Plans without markers: skip this.

Deviation Handling: If you must deviate from the plan:

• Note WHAT changed
• Note WHY it changed
• Continue with the deviation documented

PHASE_3_CHECKPOINT:

• All tasks executed in order
• Each task passed type-check
• Deviations documented

Phase 4: VALIDATE - Full Verification

4.1 Static Analysis

Run the type-check and lint commands from the plan's Validation Commands section.

Common patterns:

• JS/TS: {runner} run type-check && {runner} run lint
• Python: ruff check . && mypy .
• Rust: cargo check && cargo clippy
• Go: go vet ./...

Must pass with zero errors.

If lint errors:

1. Run the lint fix command (e.g., {runner} run lint:fix, ruff check --fix .)
2. Re-check
3. Manual fix remaining issues

4.2 Unit Tests

You MUST write or update tests for new code. This is not optional.

Test requirements:

1. Every new function/feature needs at least one test
2. Edge cases identified in the plan need tests
3. Update existing tests if behavior changed

Write tests, then run the test command from the plan.

Common patterns:

• JS/TS: {runner} test or {runner} run test
• Python: pytest or uv run pytest
• Rust: cargo test
• Go: go test ./...

If tests fail:

1. Read failure output
2. Determine: bug in implementation or bug in test?
3. Fix the actual issue
4. Re-run tests
5. Repeat until green

4.3 Build Check

Run the build command from the plan's Validation Commands section.

Common patterns:

• JS/TS: {runner} run build
• Python: N/A (interpreted) or uv build
• Rust: cargo build --release
• Go: go build ./...

Must complete without errors.

4.4 Integration Testing (if applicable)

If the plan involves API/server changes, use the integration test commands from the plan.

Example pattern:

# Start server in background (command varies by project)
{runner} run dev &
SERVER_PID=$!
sleep 3

# Test endpoints (adjust URL/port per project config)
curl -s http://localhost:{port}/health | jq

# Stop server
kill $SERVER_PID

4.5 Edge Case Testing

Run any edge case tests specified in the plan.

PHASE_4_CHECKPOINT:

• Type-check passes (command from plan)
• Lint passes (0 errors)
• Tests pass (all green)
• Build succeeds
• Integration tests pass (if applicable)

Phase 5: REPORT - Create Implementation Report

5.1 Create Report Directory

# --- PRP store resolver (canonical; keep byte-identical across skills) ---
_gd="$(git rev-parse --path-format=absolute --git-common-dir 2>/dev/null)"
case "$_gd" in */.git) _root="${_gd%/.git}" ;; "") _root="$PWD" ;; *) _root="$_gd" ;; esac
_root="$(cd "$_root" && pwd -P)"
_name="$(basename "$_root" | tr '[:upper:]' '[:lower:]' | tr -cs 'a-z0-9' '-' | sed 's/^-*//;s/-*$//')"
PRP_DIR="${PRP_HOME:-$HOME/.prp}/${_name:-project}-$(printf %s "$_root" | git hash-object --stdin | cut -c1-8)"
mkdir -p "$PRP_DIR"; [ -f "$PRP_DIR/project.json" ] || printf '{"path": "%s", "name": "%s"}\n' "$_root" "${_name:-project}" > "$PRP_DIR/project.json"
mkdir -p "$PRP_DIR/reports"

5.2 Generate Report

Path: $PRP_DIR/reports/{plan-name}-report.md

# Implementation Report

**Plan**: `$ARGUMENTS`
**Source Issue**: #{number} (if applicable)
**Branch**: `{branch-name}`
**Date**: {YYYY-MM-DD}
**Status**: {COMPLETE | PARTIAL}

---

## Summary

{Brief description of what was implemented}

---

## Assessment vs Reality

Compare the original investigation's assessment with what actually happened:

| Metric     | Predicted   | Actual   | Reasoning                                                                      |
| ---------- | ----------- | -------- | ------------------------------------------------------------------------------ |
| Complexity | {from plan} | {actual} | {Why it matched or differed - e.g., "discovered additional integration point"} |
| Confidence | {from plan} | {actual} | {e.g., "root cause was correct" or "had to pivot because X"}                   |

**If implementation deviated from the plan, explain why:**

- {What changed and why - based on what you discovered during implementation}

---

## Tasks Completed

| #   | Task               | File       | Status |
| --- | ------------------ | ---------- | ------ |
| 1   | {task description} | `src/x.ts` | ✅     |
| 2   | {task description} | `src/y.ts` | ✅     |

---

## Validation Results

| Check       | Result | Details               |
| ----------- | ------ | --------------------- |
| Type check  | ✅     | No errors             |
| Lint        | ✅     | 0 errors, N warnings  |
| Unit tests  | ✅     | X passed, 0 failed    |
| Build       | ✅     | Compiled successfully |
| Integration | ✅/⏭️  | {result or "N/A"}     |

---

## Files Changed

| File       | Action | Lines     |
| ---------- | ------ | --------- |
| `src/x.ts` | CREATE | +{N}      |
| `src/y.ts` | UPDATE | +{N}/-{M} |

---

## Deviations from Plan

{List any deviations with rationale, or "None"}

---

## Issues Encountered

{List any issues and how they were resolved, or "None"}

---

## Tests Written

| Test File       | Test Cases               |
| --------------- | ------------------------ |
| `src/x.test.ts` | {list of test functions} |

---

## Next Steps

- [ ] Review implementation
- [ ] Create PR: `gh pr create` (if applicable)
- [ ] Merge when approved

5.3 Update Source PRD (if applicable)

Check if plan was generated from a PRD:

• Look in the plan file for Source PRD: reference
• Or check if plan filename matches a phase pattern

If PRD source exists:

1. Read the PRD file
2. Find the phase row in the Implementation Phases table
3. Update the phase:
   • Change Status from in-progress to complete
4. Save the PRD

5.4 Update Plan Lifecycle & Amendments

If the plan has a ## Lifecycle (append-only) / ## Amendments section (newer template), update it before archiving — append-only, never overwrite existing entries:

• Append today's ISO-8601 timestamp to Modified
• Append the implementing commit SHA(s) to Commits
• Append your agent/model + session id to Agent / Session
• Append one Amendments entry (newest at bottom) summarizing what was built and any deviations

Older plans without these sections: skip this step.

5.5 Archive Plan

Only archive a plan that already lives in the project's store; leave a plan supplied from any other path in place.

PLAN_PATH="$(cd "$(dirname "$ARGUMENTS")" && pwd -P)/$(basename "$ARGUMENTS")"
case "$PLAN_PATH" in
  "$PRP_DIR"/plans/*)
    mkdir -p "$PRP_DIR/plans/completed"
    mv "$PLAN_PATH" "$PRP_DIR/plans/completed/"
    ;;
  *) echo "Plan is outside the PRP store; leaving it in place: $PLAN_PATH" ;;
esac

PHASE_5_CHECKPOINT:

• Report created at $PRP_DIR/reports/
• PRD updated (if applicable) - phase marked complete
• Plan Lifecycle/Amendments updated (if the plan uses them)
• Plan moved to completed folder

Phase 6: OUTPUT - Report to User

## Implementation Complete

**Plan**: `$ARGUMENTS`
**Source Issue**: #{number} (if applicable)
**Branch**: `{branch-name}`
**Status**: ✅ Complete

### Validation Summary

| Check      | Result          |
| ---------- | --------------- |
| Type check | ✅              |
| Lint       | ✅              |
| Tests      | ✅ ({N} passed) |
| Build      | ✅              |

### Files Changed

- {N} files created
- {M} files updated
- {K} tests written

### Deviations

{If none: "Implementation matched the plan."}
{If any: Brief summary of what changed and why}

### Artifacts

- Report: `{expanded absolute path to $PRP_DIR/reports/{name}-report.md}`
- Plan archived to: `{expanded absolute path to $PRP_DIR/plans/completed/}` (only when the input plan already lives in the store)

{If from PRD:}
### PRD Progress

**PRD**: `{prd-file-path}`
**Phase Completed**: #{number} - {phase name}

| # | Phase | Status |
|---|-------|--------|
{Updated phases table showing progress}

**Next Phase**: {next pending phase, or "All phases complete!"}
{If next phase can parallel: "Note: Phase {X} can also start now (parallel)"}

To continue: `the prp-plan skill {prd-path}`

### Next Steps

1. Review the report (especially if deviations noted)
2. Create PR: `gh pr create` or `the prp-pr skill`
3. Merge when approved
{If more phases: "4. Continue with next phase: `the prp-plan skill {prd-path}`"}

Handling Failures

Type Check Fails

1. Read error message carefully
2. Fix the type issue
3. Re-run the type-check command
4. Don't proceed until passing

Tests Fail

1. Identify which test failed
2. Determine: implementation bug or test bug?
3. Fix the root cause (usually implementation)
4. Re-run tests
5. Repeat until green

Lint Fails

1. Run the lint fix command for auto-fixable issues
2. Manually fix remaining issues
3. Re-run lint
4. Proceed when clean

Build Fails

1. Usually a type or import issue
2. Check the error output
3. Fix and re-run

Integration Test Fails

1. Check if server started correctly
2. Verify endpoint exists
3. Check request format
4. Fix implementation and retry

Success Criteria

• TASKS_COMPLETE: All plan tasks executed
• TYPES_PASS: Type-check command exits 0
• LINT_PASS: Lint command exits 0 (warnings OK)
• TESTS_PASS: Test command all green
• BUILD_PASS: Build command succeeds
• REPORT_CREATED: Implementation report exists
• PLAN_ARCHIVED: Original plan moved to completed