fix(basket): stop logging expected conditions as errors in Axiom

[izadoesdev]

What

Follow-up to #589. Basket's Axiom error signal is ~100% noise: of 3.18M weekly level=error events, 3,169,529 (99.7%) are Event quota exceeded — a normal billing state (customer hit their plan limit). Rate limits, invalid client IDs, unauthorized origins, and a handled Redpanda→ClickHouse fallback are also logged as errors. Real errors (e.g. Failed to get website by ID, 135/wk) are drowned ~20,000:1, making error-rate alerting meaningless.

Root cause

The evlog Elysia plugin logs every thrown error via state.logger.error(err) and drops the error's status. Basket's onError marks 4xx as isExpectedClientError but doesn't downgrade the already-set level, and the drain's old 4xx→warn check keyed off error.status, which is gone by drain time (only error_message survives).

Fix

1. Client errors → warn. Make the raw error spec the single source of truth in structured-errors.ts and derive CLIENT_ERROR_MESSAGES (messages with 4xx status) from it. The Axiom drain downgrades error → warn (+client_http_error) when http_status is 4xx or error_message is a known catalog client error. Ordering-independent — keys only off fields that survive to the drain.
2. Handled Redpanda fallback → warn. The connection failure recovers via direct ClickHouse insert, so it's log.warn, not captureError.

Test

New evlog-basket.test.ts covers the downgrade matrix (catalog 4xx → warn, http_status 4xx → warn, 5xx catalog stays error, unknown stays error, string-error flattening). Full basket suite: 606 pass (vitest run); check-types green.

Follow-up

Once deployed, basket's error-rate panels/alerts will reflect real failures instead of quota noise.

---

Summary by cubic

Downgraded expected client HTTP errors to warn in Axiom and reclassified the Redpanda→ClickHouse fallback as warn, so Basket’s error signal reflects real failures instead of quota noise. Extracted Axiom drain helpers to @databuddy/shared/evlog-axiom and adopted them in Basket.

• Bug Fixes

  • Downgrade events to warn (+client_http_error) in the Axiom drain when http_status is 4xx or error_message matches client errors derived from the catalog.
  • Flatten string error into error_message before classification for consistent handling.
  • Use log.warn for the handled Redpanda connection failure that falls back to direct ClickHouse insert.

• Refactors

  • Moved the batched Axiom drain and HTTP enrichers to @databuddy/shared/evlog-axiom and switched Basket to use them.
  • Basket keeps catalog-driven client-error detection and calls the shared downgradeClientHttpError after normalization.

^{Written for commit 021e11e. Summary will update on new commits.}

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[greptile-apps]

Greptile Summary

The PR reduces noisy Basket error telemetry by classifying known 4xx conditions and recoverable Redpanda connection failures as warnings.

• Derives client-error messages directly from Basket’s structured error specification.
• Normalizes Axiom events using surviving HTTP-status and catalog-message fields.
• Logs Redpanda connection fallback at warning level while retaining error reporting for failed ClickHouse inserts.
• Adds focused normalization and producer-delivery tests.

Confidence Score: 5/5

The PR appears safe to merge, with recoverable and expected conditions downgraded without suppressing downstream fallback-insert failures.

The normalization is limited to error-level events with numeric 4xx statuses or messages derived from the structured 4xx catalog, while unknown and server-side errors retain their level; failed ClickHouse fallback inserts continue to be captured as errors.

Important Files Changed

Filename	Overview
apps/basket/src/lib/evlog-basket.ts	Normalizes string errors and downgrades error-level events when a numeric 4xx status or known client-error message survives to the Axiom drain.
apps/basket/src/lib/structured-errors.ts	Extracts the error catalog specification into a constant and derives the 4xx message set from that single source of truth.
apps/basket/src/lib/producer.ts	Reclassifies recoverable Redpanda connection failures as warnings while preserving separate error capture for failed direct ClickHouse persistence.
apps/basket/src/lib/evlog-basket.test.ts	Adds coverage for catalog and status-based downgrades, retained server errors, unknown errors, and string-error flattening.
apps/basket/src/lib/producer.delivery.test.ts	Updates delivery tests to verify that a shared connection failure emits one warning instead of one captured error.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  E[Basket telemetry event] --> N[Normalize for Axiom]
  N --> C{Error level and client 4xx?}
  C -->|Yes| W[Emit warning with client_http_error]
  C -->|No| K[Preserve existing level]
  R[Redpanda connection failure] --> F[Select direct ClickHouse fallback]
  F --> L[Emit warning]
  F --> I{ClickHouse insert succeeds?}
  I -->|Yes| S[Delivery completes]
  I -->|No| X[Capture fallback failure as error]

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