Closes the gap identified in the L8 audit (PR #250): the four-tier
memory model (ADR-0055) designates T1 (session vault) as a source for
contemplation evidence, but _emit_discovery_candidates was calling
contemplate(c) with no vault_probe, so inline contemplation operated
on pack + reviewed corpus only.
Changes:
- core/config.py: add RuntimeConfig.vault_probe_discoveries (default
False) — opt-in flag that enables the vault probe; default-off
preserves all pre-W-016 discovery output byte-identically.
- chat/runtime.py: add _build_vault_probe(vault, vocab) module helper
that closes over the live session vault and returns a _VaultProbe
callable querying at EpistemicStatus.COHERENT (ADR-0021 §3 — only
reviewed-coherent entries contribute evidence; SPECULATIVE/CONTESTED/
FALSIFIED entries are excluded by vault.recall min_status filter).
_emit_discovery_candidates now passes the probe to contemplate() when
vault_probe_discoveries is True.
- tests/test_discovery_contemplation_vault_probe.py: four contracts
pinned — probe not called by default, probe called when flag on,
probe evidence reachable in emitted JSONL, raising probe does not
crash the loop (defensive: vault unavailability must not block
discovery).
Lane SHAs: 7/7 unchanged (demo_composition, public_demo, et al).
Smoke suite: 67/67. Teaching suite: 17/17. New test: 4/4.
Out of scope: W-017 (automated T1/T2 → T3 promotion) is a separate
ratchet entry. This PR only wires the probe.
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