Label db sync failures by real cause

[rowkav09]

Fixes #212. Mirrors the #211 worker fix in the db classifier: SyntaxError is upstream_response, and 'token' only means authentication when Plex is named. Fail-first tests in sync-failure-label.test.ts.

[rowkav09]

Reviewed head 18568b8 (on main a95344f). Approved.

Worker, plex and db suites pass (161/161, 29 files). Two of the three new tests fail against main's repository.ts. The third, the Plex token case, passes on main as well, so it only guards against regressions. I ran 15 error shapes through failSyncRun on main and on this head. These are the changes:

• SyntaxError, including a real JSON.parse failure, goes from authentication to upstream_response.
• token expired, invalid token, a uuid error mentioning a token, and a TypeError mentioning a token go from authentication to unknown.

These are unchanged and still authentication: Plex token invalid, bad X-Plex-Token, PLEX rejected the Token, plex token request timeout and bad credentials. An error that carries its own classification still wins, even a SyntaxError.

Two things to be aware of, neither blocking:

• A SyntaxError from anywhere in the sync, such as a bad config parse, now shows "Plex returned an unexpected response".
• A Plex error that says only "token" and never "plex" now shows as unknown instead of authentication. That is the trade-off you chose.

CI at the time I checked: TypeScript workspace, Compose config and CodeFactor green. The four container builds were still running, so it is not CI-green yet.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
packages/db/src/repository.ts	50.00%	0 Missing and 1 partial ⚠️

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