Agentic software factory Part 7: pr-flow skill

[cliffhall]

Part of the agentic software factory tracker #4858, Wave 3. Proposed as S6 in docs/agent-guidance-inception.md (PR #4861) §9, from #4859.

Depends on

After Part 2 (AGENTS.md), Part 3 (skills infrastructure) and Part 6 (board-ops/issue-create), whose board recipes it uses.

Scope

Adapt the Inspector's pr-flow skill (§6 of the doc):

1. Read the issue, including every comment. Assign it and move the card to In Progress.
2. Branch v2/<type>/<N>-<slug> from origin/v2/main.
3. Run the gate.
4. Open the PR with Closes #N as the first line of the body, then link it with addCloseIssueReferences and move the card to In Review.
5. Run the Copilot review loop to exhaustion: request via requestReviews with the bot id, wait for the round to post or the session to end, then decide on another round.
6. Reply in each thread, then post a PR-level summary. Decline scope creep, with a reason.
7. On merge, close the issue by hand and move the card to Done.

Two differences from the Inspector:

• Client evidence replaces screenshots. A PR that changes server behavior records what both the Inspector V2 and an LLM client were asked to do and what they returned, in both spec eras (Tracker: 2026-07-28 Spec Refactor #4857). A change with no client-observable surface (docs, skills, workflows, gate tooling) carries a targeted probe instead.
• DCO: there is no DCO app here. Record the maintainers' decision (§10 of the doc).

Acceptance criteria

• A PR has been taken end to end through the skill.
• The review loop's exits are documented: clean round, out-of-scope only, two silent rounds, timeout.
• The skill carries eval cases that pass the threshold.
• If this is the first skill PR to merge, remove Part 3's empty-skills bootstrap allowance from verify:skills.

Branch

Targets v2/main. Closes #N won't auto-close an issue on a non-default branch, so close this one by hand on merge and move the card to Done.