Soul pass 3 (R1): with no error handler, Fastify answered a 5xx with the
error's message. A store failure under a misbound database URL reached an
anonymous caller as `getaddrinfo ENOTFOUND <host>` or `database "<db>" does
not exist`, and a misbound URL puts part of the password in either. The same
default quoted the request body in a JSON parse error (Node's JSON.parse
message carries the input), the Content-Type header in a 415, and the path
in a 404.
buildApp now sets both handlers. A 5xx answers `{ error: "internal_error" }`
and writes one stderr line naming the method, the route pattern and the
error code. A schema failure answers the failed rules by schema path and
Ajv message, which come from the route's schema. Any other 4xx answers
`invalid_request` with the error code. An unknown route answers `not_found`.
The app's own answers had two more echoes: `unknown_app` quoted the slug,
and a failed provider callback put the caught error's text in the browser
page and the backend handoff (the JSON answer was already fixed). Both are
fixed text now; the full callback error stays in the audit event.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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