feat: add implement-issue skill for dispatching child agents via worktree isolation (#7)

common/engineering/README.md

@@ -2,6 +2,7 @@
 
 ## User-invoked
 
+- [implement-issue](implement-issue/SKILL.md) — Dispatch a child agent in an isolated git worktree to implement a ready-for-agent issue end-to-end.
 - [grill-with-docs](grill-with-docs/SKILL.md) — A relentless interview to sharpen a plan or design, which also creates docs (ADRs and glossary) as we go.
 - [improve-codebase-architecture](improve-codebase-architecture/SKILL.md) — Scan a codebase for deepening opportunities, present them as a visual HTML report, then grill through whichever one you pick.
 - [project-context-pack](project-context-pack/SKILL.md) — Build and refresh a bounded repo context memory file so agents use disciplined search instead of repeated browsing.

common/engineering/implement-issue/SKILL.md

@@ -0,0 +1,143 @@
+---
+name: implement-issue
+disable-model-invocation: true
+---
+
+# Implement Issue
+
+Dispatch a child agent in an isolated git worktree to implement a `ready-for-agent` issue end-to-end — explore, implement with TDD, run the full quality gate, push a branch, create a PR, comment on the issue, and update labels.
+
+The issue tracker conventions live in [`docs/agents/issue-tracker.md`](../../../docs/agents/issue-tracker.md) and the triage label vocabulary in [`docs/agents/triage-labels.md`](../../../docs/agents/triage-labels.md). Both should have been provided to you already.
+
+## Process
+
+### 1. Pre-flight checks
+
+Stop on any failure and report clearly what needs fixing. Do not proceed.
+
+#### 1a. `tea` CLI
+
+Confirm `tea` is on PATH. If missing, tell the user to install it and stop.
+
+#### 1b. Issue exists and is open
+
+```bash
+tea issue <N> -o json
+```
+
+If the issue is not found (404) or state is not `open`, report and stop.
+
+#### 1c. Issue is labeled `ready-for-agent`
+
+Check that the issue's labels include `ready-for-agent`. If not, report the current state and point the user to `/triage`. Stop.
+
+#### 1d. No open blockers
+
+Read the issue body for "Blocked by #M" references. For each referenced issue, check whether it is open:
+
+```bash
+tea issue <M> -o json
+```
+
+If any blocker is open, report the blocking issues and stop.
+
+#### 1e. Remote exists and base branch is reachable
+
+Default base is the repo's default branch — infer from `git ls-remote --heads origin` (look for `main` or `master`). Allow an explicit `--base <branch>` override.
+
+```bash
+git ls-remote --heads origin <base>
+```
+
+If the remote is unreachable or the base branch doesn't exist, report and stop. SSH auth issues (e.g. `Permission denied (publickey)`) are a failure — tell the user which key is needed.
+
+> **SSH note:** `tea` uses HTTPS and may work when git-over-SSH does not. If the first `git ls-remote` fails with an SSH error, try `export SSH_AUTH_SOCK=$(gpgconf --list-dirs agent-ssh-socket)` and retry before failing.
+
+#### 1f. Branch name is free
+
+Derive the branch name from the issue title:
+
+- Format: `issue-<N>-<slug>`
+- Slug: lowercase the title, strip to `[a-z0-9-]`, truncate to ~4–5 short words (max ~50 chars), collapse double hyphens
+- If the title yields no usable slug, fall back to `issue-<N>`
+
+Check that the branch doesn't already exist on the remote:
+
+```bash
+git ls-remote --heads origin <branch-name>
+```
+
+If it exists, report and stop. (No auto-suffix, no force-push.)
+
+#### 1g. Worktree path is free
+
+The worktree path is a sibling to the main repo: `../<repo-name>-issue-<N>`. Check that it doesn't already exist:
+
+```bash
+ls -d ../<repo-name>-issue-<N>
+```
+
+If it exists, report and stop. Let the user override with `--force`.
+
+### 2. Setup
+
+#### 2a. Fetch latest base
+
+```bash
+git fetch origin <base>
+```
+
+#### 2b. Label the issue `in-progress`
+
+```bash
+tea issues edit <N> --add-labels "in-progress" --remove-labels "ready-for-agent"
+```
+
+#### 2c. Create the worktree
+
+```bash
+git worktree add -b <branch-name> ../<repo-name>-issue-<N> <base>
+```
+
+### 3. Compose the child prompt
+
+Assemble a single prompt that the child agent will receive. Include:
+
+- **Issue body** — the full markdown body from `tea issue <N> -o json`
+- **Comments** — all comments, if any
+- **Standing instruction**: "Implement using TDD: write a failing test first, make it pass, refactor. Explore the codebase before writing code. Respect ADRs and the project domain glossary. Set up the project (install dependencies, build) before starting. The issue body may contain Implementation Decisions and Testing Decisions sections — treat these as constraints."
+- **Context**: "Base branch: `<base>`. Target your PR at `<base>`. Branch name: `<branch-name>`."
+- **Checklist** — a numbered checklist the child should work through:
+  1. Explore the codebase and read the issue body + comments thoroughly
+  2. Install dependencies and build the project
+  3. Implement the change using TDD (red-green-refactor)
+  4. Run the full project quality gate (infer from package.json, Makefile, Cargo.toml, etc.), fix until green
+  5. Commit with conventional commits (`feat:` for enhancement, `fix:` for bug) referencing `(#<N>)`
+  6. Push the branch: `git push origin <branch-name>`
+  7. Create a PR with: link to the issue, one-sentence summary, short key-changes list
+  8. Comment on the issue with the PR link: `tea comment <N> "PR opened: <url>"`
+  9. Change the issue label to `in-review`: `tea issues edit <N> --add-labels "in-review" --remove-labels "in-progress"`
+  10. Print `DONE — issue #<N>`
+- **Failure instruction**: "If any step fails, report where you stopped and what remains for manual recovery. Print the exact commands needed."
+
+### 4. Launch the child
+
+Open a new tmux window in the worktree directory and run `pi` with the composed prompt:
+
+```bash
+tmux new-window -c <absolute-worktree-path> "pi --prompt '<escaped-prompt>'"
+```
+
+The pane stays open after the child completes so the user can review the output.
+
+### 5. Print summary
+
+After launching, print:
+- Issue number and title
+- Worktree path
+- Branch name
+- Base branch
+- Tmux window (so the user can find it)
+- Cleanup command: `git worktree remove <worktree-path> && git worktree prune`
+
+The parent's turn ends here. The user can dispatch another issue immediately.