playbooks: repo-sweep next does not detect a sweep PR that CI has stopped testing

[kyle-sexton]

/playbooks:repo-sweep next pushes one commit per step but never checks that CI ran on it. In melodic-software/.github#153, main moved during the sweep (#158 re-pinned .cursor/install.sh), and the PR became mergeable: CONFLICTING. GitHub does not run pull_request workflows on a conflicting PR, so the last six step commits (5ebec0e..a0b83b9) got no CI run. state.sh and every step reported normally; the gap surfaced only during a manual review after the final verify step.

Fix: have state.sh read gh pr view --json mergeable and report mergeable CONFLICTING as a warning line (or a new exit code). Have next section 1 stop on it and tell the user to merge the base before running the next step. That way each step's commit is tested by CI before the next step builds on it.

Evidence: gh run list --branch chore/repo-sweep-hygiene-20260926 shows the newest run on head 7c794ea, while the PR head is a0b83b9. git merge-tree reports a conflict in .cursor/install.sh.

🤖 Generated with Claude Code

https://claude.ai/code/session_01S5b57FoPJkJMe1BDwhExiG

[kyle-sexton]

This was generated by AI during triage.

Agent Brief

Type: Feature
Summary: repo-sweep next stops when the sweep PR conflicts with its base.

Current behavior:
state does not read the PR's mergeable state, so next keeps stepping on a PR that CI has stopped testing.

Desired behavior:
state reads gh pr view --json mergeable and prints a mergeable CONFLICTING warning line; next stops on it and tells the user to merge the base first. Only CONFLICTING stops (UNKNOWN is common right after a push).

Acceptance criteria:

• With a conflicting PR, next stops before the step and names merging the base.
• No new exit code.

[kyle-sexton]

This was generated by AI during triage.

Decision defaulted: a warning line plus a stop in next, no new exit code — veto before merge
Basis: judgment, reversible; exit codes are consumed by next and tests, an added line is additive