feedback (validated): brain vector signal confirmed in fresh processes on v0.15.0; conceptual-query noise + embed-tier ceiling remain

[ajianaz]

Summary

External user feedback on brain search quality has been validated. On binaries \u22640.14.x, brain search silently degraded to FTS+graph in fresh processes (root cause #545). Fix shipped via #546 in v0.15.0. This issue records the validation evidence and the remaining (non-bug) quality feedback.

Validation evidence (v0.15.0)

Repo: cora-code self-index, 1,220 symbols / 134 files, embedding tier hashing-trick (256d, static).

Test	Binary	Result
Fresh-process conceptual query (\u0022why does search degrade to keyword only fallback in a new process\u0022)	v0.15.0	20/20 results carry vector signal
Same query, same index	v0.13.0	0 results (vector never fired, FTS+graph returned nothing useful)
Exact-term query (ensure_vector_cache)	v0.15.0	Fusion works: top-1 = [fts, vector], score ~2.3\u00d7 vector-only hits
cora explore 'vector_search'	v0.15.0	1 precise hit, instant

vecq backend note: the documented fresh-process degradation (vecq#32) is closed by #548 (vecq-core 0.3.0 keyed persistence) \u2014 so on v0.15.0 both backends should fire vector in fresh processes. vecq path not re-verified at runtime locally.

Remaining feedback (quality, not bug)

1. Conceptual queries still surface noise in top-10 (e.g. regex constants from extract.rs rank high for a prose query about process-boundary degradation).
2. Current static hashing 256d embed tier caps semantic depth \u2014 the vector signal is now wired end-to-end, but embedding quality is the next ceiling.

Proposed follow-ups

• Confirm the reporter is on v0.15.0 (their symptom matches \u22640.14.x behavior)
• Treat ranking tuning (RRF weighting / conceptual-query noise) as input to research: small CPU-only code embeddings + adoptable optimizations from peer tools (embed tier roadmap) #544 (embed tier roadmap) and feat(brain): ONNX runtime integration with Jina v2 base code embeddings #500 (ONNX Jina), which is the real quality lever

/cc validation session 2026-09-01