fix(fb-33): address PR #124 round 1 review

- pipeline: refresh module docstring step 5 to reflect new cancel
  semantics (RetrievalDone/Token/Final + LlmStreamAborted)
- wire schema: spell out refusal-path behavior in answer_event.v1
  description (only retrieval_done emitted; no final)
- test: factual comment on relax_score_gate-using test corrected
- test: new Ollama-gated stream_score_gate_refusal_emits_only_retrieval_done
- test: new ask_emits_no_final_when_cancelled_mid_stream pinning
  the no-Final invariant on cancel
- pipeline: large_enum_variant comment broadened to acknowledge
  RetrievalDone.hits as the dominant per-emit cost
- HOTFIXES: log AskOpts.stream_sink internal API break per spec
  contract policy

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/wire-schema/v1/answer_event.schema.json

@@ -2,7 +2,7 @@
   "$schema": "https://json-schema.org/draft/2020-12/schema",
   "$id": "https://kb.local/wire/v1/answer_event.schema.json",
   "title": "AnswerEvent v1",
-  "description": "Streaming event emitted by `kebab ask --stream`. One event per line on stderr (ndjson). Discriminated by `kind`. Terminal: `final`. Final stdout line is `answer.v1` for backwards compat (see ingest_progress.v1 precedent).",
+  "description": "Streaming event emitted by `kebab ask --stream`. One event per line on stderr (ndjson). Discriminated by `kind`. The success path closes with `final`; refusal paths (score_gate / no_chunks) emit only `retrieval_done` and rely on the stdout `answer.v1` line for the canonical signal. Cancel paths (BrokenPipe) may emit any prefix and stop. Final stdout line is always `answer.v1` for backwards compat (see ingest_progress.v1 precedent).",
   "type": "object",
   "required": ["schema_version", "kind", "ts"],
   "properties": {