Encoding worker infra/auth failures: retry instead of terminal-failing the job

[beveradb]

Why

Prod alert burst (2026-08-31): a paying customer's job (6452888e) was terminally failed — its render worker error was:

Encoding job 6452888e failed: Failed to retrieve https://metadata.google.internal/.../service-accounts/default/ … Compute Engine Metadata server unavailable … SSLCertVerificationError

Root cause: the c4d primary pair was in a zonal stockout (503 on start), so the render fell back to encoding-worker-fallback-c4a. That fallback VM booted and accepted the job but then couldn't reach the GCE metadata server to fetch its service-account token, so it couldn't touch GCS and died mid-encode. This surfaced as a bare RuntimeError, hit render_video_worker's generic except Exception → fail_job, and lost the job with no retry — even though the exact same work succeeds on any healthy worker.

The same alert burst also included the daily E2E happy-path failure (the encoder being offline made the preview step flaky) and a benign match-judge AI call failed; returning no-suggestion red-error page. All three are addressed here.

What

1. Encoding infra/auth failures are now recoverable (primary fix)

• encoding_errors.py: is_worker_infra_error() classifier (metadata / SSL-cert / missing-credentials markers, deliberately specific so a real ffmpeg/input error never matches) + new EncodingWorkerInfraError — a subclass of EncodingWorkerStartError so it flows through the existing park-for-auto-retry path with zero changes to the render worker's except (and the final-encode Cloud Run Job retries too).
• encoding_service.wait_for_completion(): on a worker-reported infra/auth failure, demote the broken worker + invalidate the URL cache, then raise the recoverable typed error instead of RuntimeError.
• encoding_worker_manager.demote_active_worker(): records a capacity-state cooldown for the serving fallback's machine_type@zone and clears active_override, so the retry re-selects a different, healthy VM. Scoped to fallbacks only — it never family-demotes the fast c4d primary on a rare blip.

2. match-judge noise — the two graceful-degradation logger.exception calls become logger.warning(exc_info=True), so a transient Vertex/Gemini blip that safely returns no-suggestion stops paging as a red "new error pattern".

3. Happy-path E2E robustness — tolerate slow encoder cold-starts at the preview step: scope the alert check to the modal (kills the spurious empty-[role=alert] "Preview error:" from run #151) and recover the "Proceed to Instrumental" button via reload+reopen. The final assertion stays authoritative, so genuinely broken generation still fails the smoke test.

Testing

• New unit coverage: classifier positive/negative + subclass (test_encoding_errors.py), demote_active_worker (fallback demote+clear, primary no-op, never-raises), wait_for_completion infra classification (+ demote/invalidate, and no-manager path), and render worker parks (not fails) on EncodingWorkerInfraError.
• python -m pytest across the encoding / worker / match-judge suites: 177 passed locally.

Not in this PR (infra, needs Andrew / GCP write)

• Fault A: encoding-worker-a (c4d, us-central1-c) is chronically 503 on start (zonal stockout) — that's why the "Encoder offline" footer showed in the E2E. This change makes the fallback path robust to it, but the underlying c4d capacity/zone choice is an infra decision (secret/VM change; my GCP access is read-only). Worth deciding whether to repin the primary family/zone or promote a fallback.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features

  • Detects infrastructure and authentication failures on encoding workers.
  • Demotes affected workers and retries jobs using alternate capacity when available.

• Bug Fixes

  • Prevents recoverable worker failures from becoming terminal job errors.
  • Reduces misleading error-level logging for gracefully handled match-judge failures.
  • Improves preview-flow recovery by waiting for actions to become enabled.

• Documentation

  • Clarified that retries prefer, but do not guarantee, a different worker.

• Chores

  • Updated the application version to 0.217.0.

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Walkthrough

The change classifies worker infrastructure failures, demotes affected fallback workers, invalidates cached URLs, and parks jobs for retry. It also adjusts match-judge logging, improves preview E2E recovery, and updates the project version to 0.217.0.

Changes

Worker infrastructure recovery

Layer / File(s)	Summary
Infrastructure error contract backend/services/encoding_errors.py, backend/tests/test_encoding_errors.py	Adds infrastructure failure markers, classification, a sentinel code, and EncodingWorkerInfraError. Tests cover matching, exclusions, subclassing, and VM-name preservation.
Worker demotion and failure routing backend/services/encoding_service.py, backend/services/encoding_worker_manager.py, backend/tests/test_encoding_service.py, backend/tests/test_encoding_worker_manager.py	Classifies failed worker jobs, demotes active fallback workers, invalidates cached URLs, and raises a recoverable typed error. Tests cover fallback demotion, primary serving, read failures, and manager absence.
Recoverable retry handling backend/tests/test_render_video_worker_capacity.py, docs/TROUBLESHOOTING.md	Verifies that infrastructure failures park jobs in RENDER_PENDING_CAPACITY and documents fallback-worker preference during auto-recovery.

Match-judge failure logging

Layer / File(s)	Summary
Graceful-degradation logging backend/services/match_judge/service.py	Changes two AI failure handlers from exception-level logs to warning logs while retaining tracebacks.

E2E recovery and release metadata

Layer / File(s)	Summary
Preview flow recovery frontend/e2e/production/happy-path-real-user.spec.ts, pyproject.toml	Scopes preview alert checks to the modal, requires the review button to be enabled, adds recovery for a disabled button, and updates the project version to 0.217.0.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: 🟡 Moderate · up to fc1e0

This change improves recovery from worker authentication and infrastructure failures, but some encoding paths can still terminally fail instead of retrying, and a failed retry trigger can leave jobs outside automatic recovery; concurrent worker changes may also misroute recovery. These are material availability risks that should be fixed or explicitly accepted before merge.

Sequence Diagram(s)

sequenceDiagram
  participant EncodingWorker
  participant wait_for_completion
  participant EncodingWorkerManager
  participant process_render_video
  EncodingWorker->>wait_for_completion: report failed job error
  wait_for_completion->>wait_for_completion: classify infrastructure markers
  wait_for_completion->>EncodingWorkerManager: demote_active_worker
  wait_for_completion->>wait_for_completion: invalidate cached URL
  wait_for_completion->>process_render_video: raise EncodingWorkerInfraError
  process_render_video->>process_render_video: transition to RENDER_PENDING_CAPACITY

Loading

Poem

A rabbit found a worker in the rain,

Its credentials had failed again.
The fallback cooled its place,
A retry began the race,
And pending capacity brought relief.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 69.57% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 9 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: encoding worker infrastructure and authentication failures now trigger retries instead of terminal job failures.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 69.57% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 23 functions across 9 files. (1 skipped: 1 unsupported.)

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Actionable comments posted: 3

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Inline comments:
In `@docs/TROUBLESHOOTING.md`:
- Line 82: Revise the troubleshooting documentation around wait_for_completion
and demote_active_worker to remove the guarantee that retries select a different
healthy worker. State that demotion applies a cooldown and makes the retry
prefer another worker, while acknowledging the same fallback may be selected if
no preferred candidate is available.

In `@frontend/e2e/production/happy-path-real-user.spec.ts`:
- Line 748: Update the proceed-button handling in the happy-path test to require
the button to be both visible and enabled before proceeding, so a visible
disabled button triggers the recovery path. Replace the visibility-only
assertion with the appropriate enabled-state check while preserving the existing
timeout and fallback behavior.
- Line 748: Replace the immediate isVisible check for proceedBtn with a waited
visibility check using waitFor({ state: "visible", timeout: TIMEOUTS.action })
or a caught toBeVisible assertion, and apply the same change to reopenBtn so
both recovery controls wait for appearance before proceeding.

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📒 Files selected for processing (11)

• backend/services/encoding_errors.py
• backend/services/encoding_service.py
• backend/services/encoding_worker_manager.py
• backend/services/match_judge/service.py
• backend/tests/test_encoding_errors.py
• backend/tests/test_encoding_service.py
• backend/tests/test_encoding_worker_manager.py
• backend/tests/test_render_video_worker_capacity.py
• docs/TROUBLESHOOTING.md
• frontend/e2e/production/happy-path-real-user.spec.ts
• pyproject.toml

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