Adds referent tracking, session graph traversal, unknown-domain gating, correction propagation, compositional surface assembly, and regression coverage.
Follow-up fixes included before merge:
- split probe/commit/finalize turn flow so unknown-domain checks run before current-query vault writes
- record real input tokens and input versors for sync and async session paths
- return true graph distances from backward walks and consume them in correction decay
- synchronize corrected graph outputs into vault-backed recall and live referent state
- regenerate correction responses from corrected context rather than correction text
- keep coreference pronouns lowercase in question bodies
- centralize elaboration-string construction to avoid plan/surface drift
- add targeted dialogue fluency regression tests
