A misconfigured embeddings endpoint failed the RAG indexer with an opaque
"Invalid JSON response" and was not caught by "Test connection" (which only
probed the chat model), so it only surfaced silently during background
indexing.
- add describeProviderError(): formats AI SDK errors as
"<statusCode>: <message> | response body: <truncated one-line snippet>"
(statusCode/message/responseBody never carry the API key)
- use it in the bulk-reindex catch and the embedding processor's formatter so
the real cause (e.g. an HTML 404 from a wrong base URL) is visible in logs
- testConnection now probes chat AND embeddings independently: skips a probe
when that capability is unconfigured, returns ok:false with a Chat:/Embeddings:
prefix on real failure, "not configured" when neither is set
b46aed53e3