fix(simkl): show why Simkl rejected a link or Client ID

[selmant]

Description

• Refs Simkl integration #8. This makes the failure diagnosable; it may not be the fix, so the issue stays open.

Linking Simkl failed with only "Request failed with status code 400". The PIN routes passed axios's generic message on and logged nothing, so neither the UI nor the server log said what Simkl, or a proxy in front of it, objected to. With a valid Client ID, Simkl's /oauth/pin and its polling endpoint behave as expected, so this PR doesn't guess at the cause. It makes the next failure explain itself:

• SimklAPI wraps rejected requests in SimklRequestError. The error carries Simkl's error/message, e.g. Simkl rejected the request (HTTP 412): client_id_failed — Your client_id is wrong. Try another one, or the text of a proxy's HTML error page.
• The PIN code and token routes log their failures.
• validateClientId now uses /oauth/pin. The CDN catalog it used before, and the title lookups, accept any Client ID; the PIN endpoint was the only one found that checks it. A rejected Client ID now fails the admin save with a 400 carrying Simkl's reason, which the settings modal shows as a toast. The integration health check logs why it degraded. It requests at most one PIN per 5-minute cache window, and the PIN expires unused.

The Rust backend (#10) is left unchanged for now.

How Has This Been Tested?

• server/api/simkl/index.test.ts (new): Simkl's reason is kept, a proxy's HTML page is reduced to text, and the Client ID check hits /oauth/pin.
• bun run test: 1174 tests, 0 failures.
• typecheck:server, eslint, prettier, bun run build.
• Ran the dev server on a copy of the config with a bogus Client ID. POST …/simkl/pin/code returns Simkl's 412 reason and logs it; saving the bogus ID in the admin settings returns 400 with the same reason.
• Against Simkl with a real Client ID: /oauth/pin returns 200 and the poll answers {"result":"KO","message":"Authorization pending"}, which the existing code already handles.

Screenshots / Logs (if applicable)

[error][API]: Failed to start Simkl PIN authorization {"errorMessage":"Simkl rejected the request (HTTP 412): client_id_failed — Your client_id is wrong. Try another one"}
[error][Settings]: Unable to save Simkl settings {"errorMessage":"Simkl rejected the request (HTTP 412): client_id_failed — Your client_id is wrong. Try another one"}

Checklist:

• I have read and followed the contribution guidelines.
• Disclosed any use of AI (see our policy) — investigation, code, and PR drafted with Claude Code
• I have updated the documentation accordingly.
• All new and existing tests passed.
• Successful build bun run build
• Translation keys bun run i18n:extract
• Database migration (if required)

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Simkl connection failures now provide clearer error details when available, while keeping excessively long messages within a reasonable limit.
  • Simkl client ID validation now checks the authorization PIN endpoint.
  • Saving invalid Simkl settings returns a clear error instead of a generic save failure.

• Reliability

  • Added warning and error logging for Simkl health checks and PIN authorization failures.

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Reviewing files that changed from the base of the PR and between a1906fe and 3b7d644.

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📒 Files selected for processing (2)

• server/api/simkl/index.test.ts
• server/api/simkl/index.ts

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📝 Walkthrough

📝 Walkthrough

Walkthrough

Simkl requests now expose structured HTTP error details, and Client ID validation uses the PIN endpoint. Settings responses and integration logs now report Simkl failures.

Changes

Simkl error handling

Layer / File(s)	Summary
Structured request errors server/api/simkl/index.ts, server/api/simkl/index.test.ts, server/routes/settings/index.ts	The API extracts error details and throws SimklRequestError for applicable failed requests. The settings route returns its message with HTTP 400. Tests cover error details and request behavior.
Validation and authorization reporting server/api/simkl/index.ts, server/api/simkl/index.test.ts, server/lib/integrationHealth.ts, server/routes/user/usersettings.ts	Client ID validation requests a PIN code. The health check and PIN authorization handlers log Simkl failures. Existing degraded health results and authorization responses remain unchanged.

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

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Pre-merge checks · 5

Passed checks (5 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely describes the main change: exposing why Simkl rejected links or Client IDs.
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 5…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @server/api/simkl/index.ts:
- Line 74: Limit the combined object-field detail produced by parts.join() to
the same maximum length used for text-response details before returning it, so
structured 4xx errors cannot create an unbounded message.

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Reviewing files that changed from the base of the PR and between 536e6d7 and a1906fe.

📒 Files selected for processing (5)

• server/api/simkl/index.test.ts
• server/api/simkl/index.ts
• server/lib/integrationHealth.ts
• server/routes/settings/index.ts
• server/routes/user/usersettings.ts

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