Probe + brake hardening: run_attempt branch identity, --all in run counting

[yihanzhu]

Follow-up from #131's review loop — two Codex P2s that arrived after the round cap. Both accepted, deferred per the productive-cap rule (edge-case robustness, not Important):

1. plumbing-test.yml: include github.run_attempt in the probe branch/PR identity — a re-run reuses run_id, so attempt 2 can collide with attempt 1's leftovers and the existence assert can pass against the stale PR.
2. quota-preflight.sh: add --all to gh run list --workflow — without it, a lane workflow disabled mid-window drops out of the count and combined usage can exceed the backstop unseen.

Comments: #131 (comment) (Codex, 2026-08-26 14:21 UTC, both 👍-reacted).

[yihanzhu]

Parked under ROADMAP step 4 (default adapters): this is GitHub-Actions-specific plumbing — run_attempt branch identity and --all run counting belong to the GitHub Actions CI adapter, with the backpressure half touching step 3 (durable orchestrator). Pre-construction issues are ineligible by default; a step-4 brief must adopt this explicitly.