Backend: POST /api/connections/{id}/test decrypts the stored config, calls
provider.OpenAsync with a 10s CancellationTokenSource, closes the returned
handle in a finally, and returns {ok: bool, error?: string}. Always 200
unless the id is unknown (404) — the outcome of the round-trip belongs in
the body, not the status. 2 new xUnit tests cover the 404 path and the
"connection refused" failure path (points at 127.0.0.1:1).
Frontend: Plug icon on each ConnectionsPage row. Click → animated icon
during the round-trip, then an inline pill: 'Connected' (green check) on
success or the truncated error (red X, full text on hover) on failure.
Auto-clears after 6s. Row state is tracked per-id in a plain useState;
the shared react-query cache stays untouched. 1 new Vitest covers both
outcomes via MSW handlers.
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