All four sources returning 0 results is a strong signal of a network
problem (DNS, firewall, proxy, Docker isolation) rather than four
independent matching bugs.
New endpoint GET /api/items/match/connectivity:
- Pings Google, MusicBrainz, OpenLibrary, GoogleBooks, DNB
- Returns per-target HTTP status, byte count, latency, error
- Surfaces any HTTP_PROXY / HTTPS_PROXY env vars that httpx would use
UI: New "Connectivity-Check" button in BookDetail. Result panel shows
each target green (HTTP 200) or red (error/timeout), so the user can
immediately see whether the backend has outbound internet access at
all, or whether it's a per-API issue.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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