feat(observability): trace, measure and log Sturnus without shipping content

[TheMeinerLP]

OpenTelemetry traces and metrics, plus structured logging shaped for Loki. Large — about 6,500 lines across 45 files, introducing sturnus/observability/ (setup, redaction, fields, events) plus infrastructure/telemetry.py and traced.py.

Redaction is an allowlist, not a denylist

Unregistered field names are dropped. bytes is dropped as a class — audio and wrapped data keys are always bytes, so the highest-value leak is closed by construction rather than by remembering. Strings are pattern-scrubbed and capped, and every replacement is visible («redacted:discord_token») rather than silent.

The leak this branch had, and how it was closed

With STURNUS_LOG_LEVEL=DEBUG the Discord voice secret_key reached the logs, and would have reached Loki. Reproduced:

discord/ext/voice_recv/gateway.py:57
  log.debug("Received op %s: \n%s", op, pformat(data))
  → {'mode': …, 'secret_key': [1, 2, …, 32], 'ssrc': …}

Not a redaction failure — extra={"secret_key": …} was dropped, and so was extra={"voice_ready": {…}}. The key arrived already formatted into a third-party logger's message string, which a field allowlist cannot touch.

The cause was root.setLevel(min(resolved_level, resolved_third_party)), which put 28 unclamped third-party loggers at DEBUG. That min() was never load-bearing: Python checks the originating logger's effective level during propagation, never root's — verified by pinning root to WARNING and watching Sturnus' DEBUG still emit while third-party DEBUG stayed suppressed. Removing it costs nothing and closes the hole.

Sentry was never affected: LoggingIntegration(level=None, event_level=ERROR) plus scrub_event reducing logentry to the uninterpolated template. Loki only.

discord.voice_state is pinned at INFO, not silenced. DEBUG is where the leak lives; INFO is the connect narrative — handshake attempts, endpoint, close codes, resume — and that is the evidence base for the capture-failure cooldown. Pinning required a NEVER_ABOVE counterpart, because NEVER_BELOW is applied as max(level, floor) and can only make a logger quieter: an INFO entry there would have been a no-op at the deployed WARNING default, silently leaving the narrative deleted.

Metrics that answer questions this project actually had

sturnus.transcription.decoded_seconds ÷ wall time is the real-time factor. A job that "finished" 100 minutes of audio in 43 seconds reports 140× — impossible, and unmistakable. The symptom everyone actually saw, an empty transcript, looked exactly like a participant who never spoke, and was read as one for a day.

position_seconds, total_seconds and seconds_since_progress are observable instruments, not synchronous gauges: a decoder that wedges freezes a gauge, so seconds_since_progress could never grow — which is the whole alert. They emit no observation when idle, so a series goes stale rather than reporting a finished job forever. The stall clock starts before the library call, because the collapse happened inside feature extraction.

Labels are model only. No session, job, guild or user id: unbounded cardinality, and a privacy leak with a very long retention.

The progress signal costs nothing — transcribe() already returns a lazy generator, and the old tuple comprehension consumed it in one expression, discarding every intermediate observation.

sturnus.job.outcome was reporting failures as successes

It recorded done for every failed job, because process_one returns True after queue.fail — it means "work was attempted". A metric that reports failures as successes is worse than none, because it will be believed. The outcome is now taken at the transition, from what happened.

Verification

777 tests pass, mypy and ruff clean. 28 mutations, all killed — including "back to a tuple comprehension", "begin() after the model call", "no top-up", "a session id becomes a metric label", and "a retry counted as done".

Squashed to one commit: two earlier ones carried a fixture with the literal shape of a Discord bot token, which GitHub's push protection blocks — correctly, whether or not that string opens anything. It is now assembled at import, identical at runtime, so the tests still prove the redaction catches that exact shape with nothing in the file for a scanner or a reader to mistake for a credential.

Worth second-guessing

• NEVER_ABOVE is new mechanism the review did not ask for. Without it the finding is unmet in production; with it there is a second dict that can hold a logger open. One entry, both directions tested.
• Queue.fail -> bool widens an application port for an observability reason. Genuinely needed to tell permanent loss from a retry, but it is a contract change.
• sturnus.queue.depth is sampled per poll, and the worker does not poll while transcribing — during a 98-minute job the reading is 98 minutes old. Documented, not fixed; fixing it needs a DB read from the exporter thread.

[gitguardian]

️✅ There are no secrets present in this pull request anymore.

If these secrets were true positive and are still valid, we highly recommend you to revoke them.
While these secrets were previously flagged, we no longer have a reference to the
specific commits where they were detected. Once a secret has been leaked into a git
repository, you should consider it compromised, even if it was deleted immediately.
Find here more information about risks.

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