skill-pr-implementation

name	skill-pr-implementation
description	PR description preparation for CSLib tasks. Analyzes task description and git diff to produce pr-description.md. Delegates to cslib-implementation-agent and transitions task to [PR READY]. Branch creation and CI are handled by the /pr command. Invoke for pr implementation tasks.
allowed-tools	Agent, Bash, Edit, Read, Write

PR Implementation Skill

Thin wrapper that delegates PR preparation work to cslib-implementation-agent subagent with PR-specific delegation context. The critical difference from skill-cslib-implementation is the postflight status transition: this skill calls pr_ready (not implement), setting the task to [PR READY] to direct the user to run /pr {task_number}.

Trigger Conditions

This skill activates when:

• Task type is "pr"
• /implement command targets a PR preparation task
• A pr-description.md needs to be composed based on the task description and git diff

Execution Flow

Stage 1: Input Validation

Validate task_number exists, task_type is "pr", and an implementation plan is present.

Stage 2: Preflight Status Update

Update status to "implementing" BEFORE invoking subagent.

bash .claude/scripts/update-task-status.sh preflight "$task_number" implement "$session_id"

Stage 3: Prepare Delegation Context

PR-specific context for the cslib-implementation-agent:

• Target output: specs/{NNN}_{SLUG}/pr-description.md (canonical PR description file)
• Diff analysis: Run git diff to analyze what changes are present on the current branch
• Standards: pr-description-format.md and pr-conventions.md (loaded via index-entries.json languages: ["pr"])
• Note: Branch creation and CI verification are handled by the /pr command

{
  "session_id": "sess_{timestamp}_{random}",
  "delegation_depth": 1,
  "delegation_path": ["orchestrator", "implement", "skill-pr-implementation"],
  "timeout": 3600,
  "task_context": {
    "task_number": N,
    "task_name": "{project_name}",
    "description": "{description}",
    "task_type": "pr"
  },
  "plan_path": "specs/{NNN}_{SLUG}/plans/MM_{short-slug}.md",
  "orchestrator_mode": true,
  "metadata_file_path": "specs/{NNN}_{SLUG}/.return-meta.json",
  "pr_description_path": "specs/{NNN}_{SLUG}/pr-description.md"
}

Important: The subagent's task is PR description composition only -- NOT branch creation, CI verification, or Lean proof implementation. The agent should:

1. Read the task description and plan to understand what was implemented
2. Run git diff (or git diff upstream/main...HEAD) to analyze changes on the current branch
3. Compose pr-description.md following the canonical format from pr-description-format.md
4. Determine base_branch (typically "main") and include it in the return metadata
5. Write .return-meta.json with status implemented when done

Stage 4: Invoke Subagent

Use Agent tool with subagent_type: "cslib-implementation-agent".

Stage 4b: Self-Execution Fallback

CRITICAL: If you performed the work above WITHOUT using the Agent tool (i.e., you read files, wrote artifacts, or updated metadata directly instead of spawning a subagent), you MUST write a .return-meta.json file now before proceeding to postflight. Use the schema from return-metadata-file.md with the appropriate status value for this operation.

If you DID use the Agent tool, skip this stage -- the subagent already wrote the metadata.

Postflight (ALWAYS EXECUTE)

The following stages MUST execute after work is complete, whether the work was done by a subagent or inline (Stage 4b). Do NOT skip these stages for any reason.

Stage 5: Parse Subagent Return

Read the metadata file from specs/{N}_{SLUG}/.return-meta.json.

Stage 6: Update Task Status (Postflight — PR READY)

CRITICAL DIFFERENCE: This skill calls pr_ready as the status target, NOT implement. This sets the task to [PR READY] instead of [COMPLETED], directing the user to run /merge.

bash .claude/scripts/update-task-status.sh postflight "$task_number" pr_ready "$session_id"

Do NOT call postflight implement -- that would incorrectly mark the task as [COMPLETED] before the PR has been submitted.

Stage 7: Link Artifacts

Add pr-description.md artifact to state.json with summary. Update TODO.md per @.claude/context/patterns/artifact-linking-todo.md with field_name=**Summary**, next_field=**Description**.

Artifact type: pr_description, path: specs/{NNN}_{SLUG}/pr-description.md.

base_branch: Also record the base branch in the state.json task entry. This field is read by the /pr command to set --base when creating the PR. Use the branch name the PR will target (e.g., "main" for direct upstream PRs, or "feat/parent-branch" for stacked PRs).

The subagent should determine and report the base branch used (typically "main" unless this task is stacked on top of another unmerged PR).

# Write base_branch to state.json task metadata
CSLIB_DIR="/home/benjamin/Projects/cslib"
CSLIB_STATE="$CSLIB_DIR/specs/state.json"
base_branch_used="main"  # or the parent branch for stacked PRs

jq --argjson num "$task_number" \
   --arg branch "$base_branch_used" \
   '.active_projects |= map(if .project_number == $num then . + {"base_branch": $branch} else . end)' \
   "$CSLIB_STATE" > /tmp/state.tmp && mv /tmp/state.tmp "$CSLIB_STATE"

Stage 8: Git Commit

Commit changes with session ID.

Stage 9: Return Brief Summary

Include a message directing the user to run /pr {task_number} now that the task is [PR READY]:

PR description complete. Task is now [PR READY]. Run /pr {task_number} to create the branch, run CI, and submit the pull request.

MUST NOT (Postflight Boundary)

After the agent returns, this skill MUST NOT:

1. Edit .lean files - All CSLib proof work is done by agent
2. Run lake build/test/lint - Verification is done by agent
3. Use lean-lsp MCP tools - Domain tools are for agent use only
4. Grep for sorries - Debt analysis is agent work
5. Write pr-description.md - Artifact creation is agent work
6. Create feature branches - Branch creation is handled by the /pr command, not this skill
7. Run CI pipeline - CI verification (lake test, lint, shake) is handled by the /pr command, not this skill
8. Call postflight implement - This skill MUST use postflight pr_ready to set [PR READY]

PROHIBITION: If the subagent returned partial or failed status, the lead skill MUST NOT attempt to continue, complete, or "fill in" the subagent's work. Report the partial/failed status and let the user re-run /implement to resume.

The postflight phase is LIMITED TO:

• Reading agent metadata file
• Updating state.json via jq (using pr_ready status target)
• Updating TODO.md status marker via Edit
• Linking artifacts in state.json
• Git commit
• Cleanup of temp/marker files

Reference: @.claude/context/standards/postflight-tool-restrictions.md

Return Format

Brief text summary (NOT JSON).