Replace plain ValueError at both inner-loop exhaustion sites in
generate/stream.py with InnerLoopExhaustion, a typed ValueError
subclass carrying machine-readable refusal evidence:
reason : RefusalReason (INNER_LOOP_EXHAUSTION)
region_label : which AdmissibilityRegion blocked
step_index : -1 = pre-walk empty intersection;
>=0 = in-walk per-step exhaustion
rejected_attempts : ordered (idx, word, score) triples
Backward-compat by construction: subclassing ValueError preserves
every pre-Phase-2 `except ValueError` handler in chat/runtime.py,
eval lanes, and tests. No edits to chat/runtime.py, field/propagate.py,
algebra/versor.py, or vault/store.py.
Trace path wired:
- CognitiveTurnResult.refusal_reason (str, default "")
- compute_trace_hash folds refusal_reason only when non-empty
-> byte-identical hashes preserved for non-refused turns
- CognitiveTurnPipeline reads via getattr from ChatResponse and
forwards into both trace_hash and result construction
Contract documented in docs/runtime_contracts.md §"Refusal contract".
Tests (tests/test_refusal_contract.py — 10 passing):
- InnerLoopExhaustion isinstance(ValueError) at both raise sites
- In-walk site carries reason/region_label/step_index>=0/
rejected_attempts with (int,str,float) triples
- Pre-walk site uses step_index=-1 sentinel + empty
rejected_attempts
- Pre-walk fires even when inner_loop_admissibility=False
- Trace hash: empty refusal_reason preserves legacy bytes;
non-empty differs; same inputs are stable
Suite results:
smoke: 67 passed
cognition: 121 passed
runtime: 19 passed
full: 1024 passed, 2 skipped
core eval cognition: 13/13, 100% intent accuracy, 100% versor closure
Residual silent path (documented as out-of-scope for Phase 2):
chat/runtime.respond()/arespond() still convert any ValueError to
"" for their public str return contract. So a refused turn today
produces surface == "" with refusal_reason == "" — the typed
evidence is unread between the raise site and the result. The
plumbing on result + trace + pipeline is in place so a future ADR
can wire materialisation (propagate exception to
ChatResponse.refusal_reason, or catch at the pipeline seam) without
re-deriving the contract.
Phase 1 (commit 3940290) and Phase 2 (this commit) were developed
in parallel with disjoint file scope to avoid conflicts.
