[maxmad64bis]

⚠️ base-red inherited: #14547

Summary

No default change: opt-in via STREAM_READINESS_STALL_RETRY (default off). When enabled and the first upstream body stalls before producing a usable event, the request runs once more through the same routing path with the same readiness budget and no account penalty, and only fails if the second attempt also stays empty. With the flag off, a stalled first body fails exactly as before.

Related Issues

• Related to fix(sse): retry direct stream readiness timeouts #14209 (same-target single retry on direct readiness timeouts; this PR retries once through the same routing path instead)
• Related to feat(resilience): make stream_terminated retryable and visible when mid-stream continuation is skipped for in-flight tool calls #11902 (orthogonal: client-side retryable signal; this PR is the server-side second attempt)
• Related to fix(resilience): STREAM_READINESS_TIMEOUT budget ignores reasoning_effort on non-codex providers and the timeout cascade #14025 (readiness budget cascade; this PR reuses the resolved budget unchanged)
• Related to fix(opencode): rotate once when a Responses stream stalls before its first byte #13484 (prior single-rotation precedent on a stalled Responses stream, first-byte scope; this PR covers the post-headers empty-body scope)
• Related to fix(sse): stop an empty Claude stream from emptying the whole combo #14314 (same stalled-empty-stream symptom on another path)

Validation

• Change type: routing
• Focused tests: tests/unit/stream-readiness-fallback.test.ts (9 tests), tests/unit/feature-flags-settings.test.ts (62 pass), tests/unit/server-owned-tool-loop-flag.test.ts (8 pass), tests/unit/feature-flags-doc-sync-static.test.ts (4 pass)
• npm run lint — ESLint on the touched files is clean
• Reconciled with release/v3.8.51 (rev-list HEAD..upstream/release/v3.8.51 = 0); focused checks rerun afterward
• Production-code changes include a new or updated automated test in this PR

Tests Added Or Updated

• tests/unit/stream-readiness-fallback.test.ts (9 tests: flag off issues no second request; readiness timeout then retry success, early-EOF same, double failure keeps second diagnostic, aborted client never retries, single-request bound, neighbor empty-turn untouched plus cooldown spy, silent-stream timeout; RED on the guard revert, GREEN with the guard)
• Neighbours replayed: empty-turn retry path untouched (no extra dispatch when the first attempt succeeds)

Coverage Notes

• open-sse/handlers/chatCore/streamReadinessFallback.ts covered by the new test, including the flag-off guard; chatCore.ts wiring (import + single call + reassignments) covered via the same test.
• src/shared/constants/featureFlagDefinitions.ts and src/shared/utils/featureFlags.ts covered by the flag-count suites (registry at 78, fail-closed helper).

Reviewer Notes

• When enabled, the worst case waits two readiness windows; the retry goes through the executor's normal selection and does not exclude the stalled account.
• chatCore.ts grows 6402 → 6426 (frozen, +24 wiring lines, own growth; rebaseline entry _rebaseline_2026_09_23_14669_empty_body_server_rotation included).
• Inherited reds qualified as inherited (failures cite files outside this PR, unchanged since the merge-base, base-red issue 🔴 Release branch not green: release/v3.8.51 #14547, normalized failure lists identical to same-base siblings): API Route Typecheck errors (auggie.ts, projectCombo.ts, empty diff $mb, non-PR files); check-env-doc-sync live-data case cites DEEP_HEALTH_CHECK_ENABLED, present on the untouched base; full npm run lint red on the base (🔴 Release branch not green: release/v3.8.51 #14547).

[diegosouzapw]

Solid extraction and a genuinely useful opt-in recovery path. Ran the new
stream-readiness-fallback suite (9/9) together with the rest of your stall/buffered-turn batch
on one merged tree — all green, and your own file-size rebaseline (6402→6426) comfortably
covers the small additions #14681 and #14639 make later, as long as this one lands first in the
batch. No blocking items; flagging for the release captain that #14209/#14314 (other authors)
also touch chatCore.ts and haven't been cross-tested against this set.

[maxmad64bis]

Rebased to a single commit on the current tip and mergeable. Ready to land first as suggested, unblocking #14681.