When chromadb's HNSW segment freezes at a stale max_elements while
sqlite keeps accumulating embeddings, the next chromadb open segfaults
the MCP server on every tool call. Adds a pure-filesystem capacity probe
(zero chromadb interaction), a `mempalace repair-status` read-only
health check, and a BM25-only sqlite fallback so the palace stays
reachable even when vector search is unavailable.
* `hnsw_capacity_status` reads sqlite + index_metadata.pickle directly
via a tight-allowlist unpickler — no hnswlib import, no segment load.
* MCP server runs the probe at startup and after every reconnect; sets
`_vector_disabled` and routes search to the sqlite FTS5 + BM25 path.
* `tool_status` and `tool_reconnect` surface the fallback state.
* Threshold tuned for chromadb 1.5.x async-flush lag (2× sync_threshold).
Igor Lins e Silva
0d349c3d86