chore: merge train 260821 — land #2295 (zero-byte coordinator recovery)

[lidge-jun]

Summary

Merge-train branch accumulating reviewed, verified bug-fix landings onto dev.

This first leg lands #2295 — fix(codex): recover proven zero-byte coordinator remnants (addresses #2291), merged as 728ca1e after:

• Adversarial review (grok-4.6, Volta): FAIL → synthesis → re-verdict pass; accepted residuals recorded in devlog/_plan/260821_bug_merge_train/020_merge_2295.md
• Focused tests 55/55, typecheck pass, privacy:scan pass
• Full suite on lidge at train head f745083 (includes latest origin/dev: fix(xai): normalize Responses web search tools #2312, feat(vision): routed describer backend — any picker-visible image-capable model (#2188) #2306, feat(xai): B2 — enable Priority Processing on the API-key transport (#1886, closes #1875) #2072): 14208 pass / 16 skip / 0 fail across 893 files, exit 0

Closes #2291 on merge (PRs target dev, so issue will be closed manually per repo convention).

Verification

• bun run typecheck — pass (train head)
• bun run test — full suite green via lidge remote runner at exact merge head (log /tmp/ocx-train-suite-r3.log)
• bun run privacy:scan — pass

Checklist

• Local CI green (full suite executed remotely on lidge; local focused runs green)
• Branch includes the latest dev commit (origin/dev merged into train before this PR)
• No open Codex/CodeRabbit findings against this head
• Ready for review

[github-actions]

✅ Deterministic PR hygiene checks passed.