End the merge cascade and give the traffic-controller ownership of CI *triggering*.
- autoupdate.yml updates PR branches with the built-in GITHUB_TOKEN instead of a PAT,
so an update push no longer auto-retriggers CI (GitHub's anti-recursion rule) — the
cascade (every merge re-runs every PR, cancel-in-progress thrashing them) is gone.
- New scheduler ci-trigger.yml -> traffic_control.py --mode trigger (re-)triggers CI
for the highest-priority PR(s) whose head SHA has absent/stale checks, a few at a
time (inflight cap), in the existing P0-P9 / broken-draft priority order — a
poor-man's merge queue reusing the priority core. It runs after autoupdate finishes
(workflow_run, race-free) plus a cron backstop plus manual dispatch.
- Triggering uses workflow_dispatch, which is EXEMPT from anti-recursion, so the
built-in GITHUB_TOKEN (actions: write) starts the run — NO PAT / secret change needed.
- ci.yml gains a workflow_dispatch trigger (pr/head_sha/reason inputs) and a per-PR
concurrency group unifying pull_request and dispatch runs; its on: pull_request path
is kept so brand-new PRs, human pushes, and fork PRs always get CI (fail-open).
Pure select_triggers / classify_sha_runs decision core added to traffic_control.py with
24 new unit tests (priority order, oldest-first fairness, inflight cap, fork skip, P0
bypass+preempt, head-SHA needy classification, and a liveness/anti-starvation simulation).
Closes#349
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
JMR-devandClaude Opus 4.8
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