Hybrid search scoped to this vault’s namespace.
Returns embedded vault pages as ranked results with citations. The vault
namespace was populated by the existing fs_sync_workflow mirroring every
write into TurboPuffer (see routes/v2/fs.py:294-313).
Telemetry: emits both store_api_activity (for the user-facing activity
feed) and store_retrieval_log (for the training-data pipeline) so vault
searches show up alongside every other retrieval call. Two retrieval logs
are written for the two-tier strategy: a vector log for the TurboPuffer
path, and a regex log if the PG grep fallback fires.