pick-slice

name	pick-slice
description	Find the next unclaimed ready-to-work slice in the Musubi vault, claim it atomically via GitHub Issue assignment, lock it, and prepare a working branch + draft PR. Use at the start of any coding session when the user hasn't specified which slice to work on.

Skill: pick-slice

Select the next slice from docs/Musubi/_slices/ that is status: ready, has all depends-on slices at status: done (or in-progress with their blocking surface landed), and has no active GitHub Issue assignee.

Rules this skill enforces

• Dual-update rule (see docs/Musubi/00-index/agent-guardrails.md#Dual-update-rule) — claiming a slice flips BOTH the GitHub Issue (assignee + status:in-progress label) AND the vault slice file's frontmatter (status, owner) in the same PR. This skill walks both updates; don't skip either half.
• Atomic-claim rule — GitHub Issue --add-assignee is the authoritative lock; re-read the Issue immediately after to detect races. Vault-file + lock-file edits are the secondary record.

When to invoke

• User says: "pick a slice", "what's next", "grab one off the board", or /pick-slice.
• Session-start hook after cloning a fresh worktree.
• After completing one slice and user says "keep going".

Do not invoke when

• The user named a specific slice. Work on that one — don't second-guess them.
• The user is asking a question about what slices exist (read-only — no claim).

Instructions

1. Scan the slice registry

cd ~/Projects/musubi  # or wherever pwd puts you
grep -l "^status: ready" docs/Musubi/_slices/slice-*.md

For each candidate, open the file and check:

• depends-on: — every listed slice must be status: done OR status: in-progress with a first-cut already merged (read the work log section).
• The slice's block list — higher-block-count = higher priority (unblocks more downstream work).

2. Check GitHub for existing claims

gh issue list --label "slice" --state open --json number,title,assignees,labels

If an issue exists for your candidate slice and has an assignee → skip, pick the next candidate. If an issue exists but is unassigned → claim it (step 3). If no issue exists → create one (step 3 alt).

3. Claim atomically

If an Issue already exists (unassigned):

gh issue edit <n> --add-assignee @me --add-label "status:in-progress" --remove-label "status:ready"

Race condition check: immediately re-read the issue. If assignees has multiple names, another agent also claimed it — apologise in an issue comment, remove your assignee, pick a different slice.

If no Issue exists for this slice:

gh issue create \
  --title "slice: <slice-id>" \
  --label "slice,status:in-progress" \
  --assignee @me \
  --body "Tracks implementation of [docs/Musubi/_slices/<slice-id>.md](docs/Musubi/_slices/<slice-id>.md).

Owns paths, specs, Test Contract: see the slice note."

4. Branch + draft PR

git switch main
git pull --ff-only
git switch -c slice/<slice-id>
# Initial empty commit so the PR can open before any file changes.
git commit --allow-empty -m "chore(slice): take <slice-id>

Claims docs/Musubi/_slices/<slice-id>.md. See issue #<n>."
git push -u origin slice/<slice-id>
gh pr create --draft \
  --base main \
  --title "feat(<scope>): <slice-id>" \
  --body "Closes #<n>. Draft — work in progress per docs/Musubi/_slices/<slice-id>.md."

5. Flip slice frontmatter

Edit docs/Musubi/_slices/<slice-id>.md:

• status: ready → status: in-progress

• owner: unassigned → owner: <your-agent-id> (e.g., eric-cc-opus47, yua-cowork, codex-gpt5)

• Append a work-log entry under ## Work log:

  ### YYYY-MM-DD HH:MM — <agent-id> — claim
  
  - Claimed slice via `pick-slice` skill. Issue #<n>, PR #<m> (draft).
  

Commit as chore(slice): flip <slice-id> to in-progress.

6. Drop the file-based lock (belt-and-braces)

touch docs/Musubi/_inbox/locks/<slice-id>.lock
echo "<agent-id>  $(date -Iseconds)  PR #<m>" > docs/Musubi/_inbox/locks/<slice-id>.lock
git add docs/Musubi/_inbox/locks/<slice-id>.lock
git commit -m "chore(lock): <slice-id>"

(Primary lock is the Issue assignee; this file is secondary and makes local-only agents visible to git-only reviewers.)

7. Report

One sentence back to the user: "Claimed <slice-id>. Issue #, branch slice/<slice-id>, draft PR #. Starting with the Test Contract." Then proceed to write tests per the slice spec — that's the next step of the slice-worker loop, not part of this skill.

Conflict resolution

• Two agents claimed the same issue at the same time → the one whose gh issue edit --add-assignee succeeded keeps it; the other observes multiple assignees on re-read and steps back. If both show as assignees, the one with the later createdAt on the self-assignment event yields. (GitHub Issue event log tells you who was first.)
• Depends-on slice isn't actually ready but slice said ready → mark the candidate status: blocked, file a question in docs/Musubi/_inbox/questions/, pick a different slice.
• No ready slices are available → tell the user. Don't make up work.