spike(eval): M17 Phase C — multimodal LLM judge gates (script + report stub) (#113)

* spike(eval): M17 Phase C — multimodal LLM judge gates (script + report stub)

Mirrors the Phase A spike protocol (scripts/m17_phase_a_validation.py +
docs/m17_phase_a_validation_report.md) for E5 — the Multimodal LLM Judge
evaluator from docs/automated_eval_design.md §E5. This unlocks the eval
loop that issues #92 and #97 are currently blocked on (both require
native-speaker listening which doesn't scale).

Script (scripts/m17_phase_c_validation.py):

- 6-clip set: 4 corpus typology spans (SV/IT/NEG/NEU, all M2a-wettest
  agg_m_30-45_001) + 2 degraded variants of sp_sv_a_0001_00 (white noise
  at +10 dB and -10 dB SNR, RMS-matched to the clean source so the
  judge is scoring spectral content, not amplitude).
- Two models: gemini-2.5-pro (audio input) and gpt-4o-audio-preview.
- Two reruns per (clip, model) for within-model variance measurement.
- Structured JSON output via a fixed schema (8 quality dimensions on a
  1-5 scale + artifacts_detected + confidence_in_assessment + summary).
- Four gate outcomes per model:
    refusal_gate         ≥ 5/6 clips scored under DV-research framing
    discrimination_gate  mean(corpus) − mean(severe-degraded) ≥ 0.5
    variance_gate        per-dim std across 2 reruns ≤ 0.5
    shay_correlation_gate Spearman ρ ≥ 0.3 vs encoded expected ranking
- Gemini BLOCK_NONE safety per design doc §E5 content-sensitivity
  guidance (research framing only — DV-content tolerance is required to
  avoid refusals on the metadata; the audio is entirely synthetic and
  contains no real persons).
- Hard budget cap via SYNTHBANSHEE_LLM_SPIKE_BUDGET_USD (default $5);
  aborts pre-flight on estimate, aborts mid-run on cumulative actual.
- --dry-run flag prints the prompt + schema without calling any API,
  for pre-flight prompt audit.
- Lazy imports for google-genai / openai so the module is cheap to
  import even without the deps installed.

Report stub (docs/m17_phase_c_validation_report.md):

- Same structure as the Phase A report (TL;DR gate table, Reproduce,
  Clip-set manifest, Gate definitions, Per-model results, Failure-mode
  notes, Recommendation matrix, Limitations, Cost report).
- All numeric cells marked TBD pending real-run results.
- Recommendation matrix is pre-filled per gate-outcome scenario so the
  go/no-go decision is mechanical once the script runs.

Cost estimate at default settings: ~$3.05 total ($0.35 Gemini + $2.70
GPT-4o), well within the $5 cap. Dry-run verified end-to-end.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* fix(spike/m17-phase-c): address all critical+high review findings before running

Critical:
- Replace wn_snr_+10db mid-anchor with synth_rate_slow_0.7x — tests synthesis
  defect detection (unnatural tempo + pitch-shift + truncated arc) instead of
  measuring only whether the model can hear noise
- Add --probe-metadata-bias flag: runs a no_arc prompt variant on corpus clips
  to measure whether emotional_expression / escalation_arc are scored from audio
  or inferred from the intensity-arc label; delta is reported per-clip per-dim
  in both results.json and report_auto.md

High:
- Add failure_reason field to JudgeResult ("ok" / "content_refusal" /
  "json_parse_error" / "api_error") so only content refusals count against the
  refusal gate; api_error and json_parse_error are retried, not penalised
- Incremental write: results_partial.jsonl is appended after each call;
  --resume loads prior results and skips completed (clip, model, run, variant)
  tuples — an API failure or budget-cap abort no longer loses all spend
- Drop shay_correlation and variance from overall_pass (advisory only);
  add notes: variance is trivially PASS at TEMPERATURE=0 greedy decoding,
  Shay rho is not statistically significant at n=4
- Discrimination gate now tests two independent arms — noise_corruption and
  synth_failure — reporting both separations; passing either arm clears the gate

Low:
- Fix report stub: gate table columns aligned with report_auto.md output,
  hand-written per-run tables removed (replaced with pointers to auto-report),
  limitations section updated to reflect all of the above

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

* docs(spike/m17-phase-c): fix module docstring — reflect two-arm discrimination gate

Update the gate bullet-list in the module docstring to match what the code
actually does after the review-fixes commit: two discrimination arms
(noise_corruption comparability + synth_failure real target), advisory notes
on variance and Shay-correlation, failure_reason semantics for refusal gate.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: shaypal5

docs/m17_phase_c_validation_report.md

@@ -0,0 +1,181 @@
+# M17 Phase C Validation Report — Multimodal LLM Judge on Hebrew Clips
+
+> **Status:** spike stub. Filled-in numbers land after the script runs against
+> real API keys. The gate tables below are skeletons — final values come from
+> `state/spikes/m17_phase_c/results.json` and the auto-generated
+> `state/spikes/m17_phase_c/report_auto.md`.
+
+This report validates the Phase C acceptance criteria from the M17 design
+doc (`docs/automated_eval_design.md` §E5 — Multimodal LLM Judge) before the
+E5 evaluator module skeleton lands. Mirrors the Phase A spike protocol that
+produced `docs/m17_phase_a_validation_report.md`.
+
+Generated: TBD. Raw data: `state/spikes/m17_phase_c/results.json` (gitignored).
+Auto-tables: `state/spikes/m17_phase_c/report_auto.md`. Degraded audio cached
+under `state/spikes/m17_phase_c/*.wav`.
+
+## TL;DR
+
+<!-- report_auto.md §"Gate outcomes" table goes here after the run. -->
+
+| Evaluator (model) | Refusal | Disc (noise) | Disc (synth) | Phase C |
+|---|---|---|---|---|
+| **E5a — `gemini-2.5-pro`** | TBD | TBD | TBD | TBD |
+| **E5b — `gpt-4o-audio-preview`** | TBD | TBD | TBD | TBD |
+
+**Phase C status: TBD.** `overall_pass = refusal AND discrimination`. Variance
+and Shay-correlation gates are advisory (see Gate definitions below). One model
+passing is sufficient to advance E5 to MVP.
+
+## Reproduce
+
+```bash
+uv pip install --python .venv/bin/python \
+    google-genai openai pydantic soundfile numpy scipy
+
+export GEMINI_API_KEY=...
+export OPENAI_API_KEY=...
+export SYNTHBANSHEE_LLM_SPIKE_BUDGET_USD=5.0   # hard cap
+
+# Optional dry run — prints the prompt + JSON schema, no API calls, no spend.
+.venv/bin/python scripts/m17_phase_c_validation.py --dry-run
+
+# Full run.
+.venv/bin/python scripts/m17_phase_c_validation.py
+
+# With metadata-bias probe (adds ~4 no-arc calls per model, ~$0.10–0.40 extra).
+.venv/bin/python scripts/m17_phase_c_validation.py --probe-metadata-bias
+
+# Resume a partial run after a failure or budget-cap abort.
+.venv/bin/python scripts/m17_phase_c_validation.py --resume
+```
+
+The script prepares 6 clip records (4 corpus typology spans + 2 degraded
+variants of `sp_sv_a_0001_00`), sends each to each model twice under the
+`with_metadata` prompt variant, parses structured JSON responses, writes partial
+results to `results_partial.jsonl` after each call, and writes final gate
+outcomes to `results.json` + an auto-generated markdown summary.
+
+## Clip set
+
+Source dir defaults to `data/m2a_wettest/agg_m_30-45_001/` (8-clip M2a-wettest
+batch — same source set as the Phase A spike). Override via
+`SYNTHBANSHEE_LLM_SPIKE_CLIP_DIR`.
+
+| Label | Source clip | Kind | Typology | Notes |
+|-------|-------------|------|----------|-------|
+| `sp_sv_a_0001_00` | sp_sv_a_0001_00 | corpus | SV | The canonical SV scene reviewed by Shay + Gemini + Claude + ChatGPT in `docs/debug_run_1/llm_feedbacks.md` |
+| `sp_it_a_0001_00` | sp_it_a_0001_00 | corpus | IT | The IT scene whose I3–I5 distress absence drove issue #97 |
+| `sp_neg_a_0001_00` | sp_neg_a_0001_00 | corpus | NEG | Hard-negative class — intense but `has_violence: false` |
+| `sp_neu_a_0001_00` | sp_neu_a_0001_00 | corpus | NEU | Neutral baseline; expected highest perceived quality |
+| `sp_sv_a_0001_00__synth_rate_slow_0.7x` | sp_sv_a_0001_00 resampled to 0.7× speed, trimmed | degraded | SV | **Synthesis-failure anchor.** Simulates over-slow TTS: unnatural tempo, pitch-shifted down, scene cut off mid-escalation. Tests whether the model can hear synthesis defects, not just noise. |
+| `sp_sv_a_0001_00__wn_snr_-10db` | sp_sv_a_0001_00 + severe white noise | degraded | SV | **Signal-corruption anchor.** RMS-matched to clean. Kept for comparability with Phase A E2/UTMOS. If a model passes this but fails the synth anchor, it can detect noise but not synthesis defects. |
+
+Shay-correlation check uses `expected_quality_rank` per clip (encoded in
+`CLIP_SOURCES`), grounded in:
+- The May-3 listening test memo (M12 breathiness failed gate; systemic
+  TTS naturalness issues).
+- The May-6 listening test (#92, aggregated naturalness backlog).
+- The 2026-04-14 multi-LLM review of `sp_it_a_0001` (`docs/debug_run_1/llm_feedbacks.md`).
+- Issue #97 finding that VIC at I3–I5 doesn't sound distressed under
+  rate+pitch alone.
+
+If/when new listening tests update the priors, update `CLIP_SOURCES` ranks
+and re-run.
+
+## Gate definitions
+
+Gates are computed **per model**. `overall_pass = refusal AND discrimination`.
+
+| Gate | Criterion | Included in `overall_pass`? | Why |
+|------|-----------|:---:|-----|
+| **Refusal** | ≥ 5/6 clips score successfully under the DV-research framing; only `content_refusal` failures count against this gate (`api_error` and `json_parse_error` are retryable infrastructure failures) | ✅ | A model that refuses on DV content under research framing can't be a production E5 backend. |
+| **Discrimination** | At least one anchor arm clears: `mean(corpus) − mean(severe degraded) ≥ 0.5`. Two arms: (1) noise-corruption (`wn_snr_-10db`), (2) synthesis-failure (`synth_rate_slow_0.7x`). A model that passes only the noise arm cannot detect synthesis defects. | ✅ | The actual failure modes we need to catch are synthesis defects, not SNR. |
+| **Variance** _(advisory)_ | Per-dimension std across 2 reruns ≤ 0.5 | ❌ | At `TEMPERATURE=0.0`, greedy decoding is deterministic → std=0 trivially. Re-run with `TEMPERATURE=0.1` and `N_RERUNS=4` for a meaningful estimate. |
+| **Shay correlation** _(advisory)_ | Spearman ρ ≥ 0.3 between model `overall_quality` and Shay's encoded rank on the 4 corpus clips | ❌ | n=4 is not statistically significant (need n≥7 for p<0.05). Treat as a directional red-flag check only — a strongly negative ρ is a hard warning signal. |
+
+## Per-clip mean overall_quality (TBD)
+
+<!-- report_auto.md §"Per-clip mean overall_quality" table goes here. -->
+
+## Metadata-bias probe (TBD)
+
+Run with `--probe-metadata-bias`. The probe sends the 4 corpus clips under a
+`no_arc` prompt variant that omits the `intended intensity arc` and
+`typology_long` metadata. The delta on `emotional_expression` and
+`escalation_arc` between `with_metadata` and `no_arc` measures how much of the
+score is read from the label vs. from the audio.
+
+<!-- report_auto.md §"Metadata-bias probe" table goes here. -->
+
+A delta > 0.5 on either dimension is a warning that the model is inflating
+those scores based on the label. If the delta is large, the discrimination gate
+result on those dimensions should be treated as unreliable.
+
+## Failure-mode notes (TBD post-run)
+
+- **Refusal posture under DV-research framing:** TBD — record any
+  `content_refusal` failures here, with the verbatim refusal text and the clip
+  that triggered it. Distinguish from `api_error` / `json_parse_error`. If
+  Gemini's BLOCK_NONE setting still produces content refusals, the design doc's
+  mitigation list (alternative framings, GPT-4o fallback) becomes the
+  recommended path.
+- **Noise-only discriminator:** TBD — if a model passes the noise arm but fails
+  the synth arm, record it here. This model can detect SNR changes but not
+  synthesis quality — it cannot serve as E5 backend.
+- **Score collapse / no-variance:** TBD — does any model give the same score
+  on every dimension across all 6 clips? If so the model isn't actually
+  listening to the audio.
+- **Metadata-bias:** TBD — compare `emotional_expression` and `escalation_arc`
+  deltas from the metadata-bias probe. If delta > 0.5, note which model and
+  which clips are affected.
+- **Anchor recommendation for MVP:** TBD — given the discrimination separation
+  pattern (noise vs synth), recommend whether the MVP needs in-prompt
+  calibration anchors (Phase 2b anchor protocol) or can rely on absolute
+  scoring alone.
+
+## Recommendation (TBD)
+
+| Outcome | Next action |
+|---------|-------------|
+| Both models pass refusal + **both** discrimination arms | Ship E5 MVP behind Gemini primary, GPT-4o fallback. Open follow-up issue for anchor-set protocol + regression CI workflow. |
+| Both models pass refusal + noise arm only | E5 can detect gross signal corruption but not synthesis defects. Defer MVP; re-spike with synthesis-failure anchors as calibration points in the prompt. |
+| One model passes refusal + synthesis discrimination arm | Ship MVP with that model as primary. Document the other model's failure mode in a follow-up issue. |
+| Either model fails REFUSAL on content_refusal | Try alternative framings before declaring failure; record framing experiments in this report. |
+| Both models FAIL synthesis discrimination | Phase C is a NO-GO for synthesis-quality gating. Pivot the eval roadmap: either commit to paid linguistic raters / crowd evaluation, or wait for next-generation multimodal audio models. |
+
+## Limitations
+
+- **n=4 corpus clips for the Shay-correlation check.** Spearman ρ at n=4 is
+  directional, not statistically significant. A future MVP-phase calibration
+  step should use ≥ 20 clips spanning the full corpus once more listening-test
+  ground truth is available.
+- **n=2 reruns at TEMPERATURE=0.** The variance gate trivially passes under
+  greedy decoding. To get a real reproducibility estimate, re-run with
+  `TEMPERATURE=0.1` and `N_RERUNS_PER_CLIP=4`.
+- **Synthesis-failure proxy via resampling.** The `synth_rate_slow_0.7x`
+  degradation changes both tempo and pitch simultaneously (a naive resampling
+  artifact), which is not exactly how TTS synthesis defects manifest. It is a
+  better proxy than white noise but still not identical to over-smoothed
+  prosody, wrong gender forms, or robotic timbre. The MVP-phase anchor set
+  should include real defective TTS renders, not just signal-domain proxies.
+- **English-trained models on Hebrew audio.** Both Gemini and GPT-4o have
+  unknown Hebrew-audio comprehension depth. If discrimination passes for both,
+  that's reassuring; if only one passes, document the Hebrew-specific failure
+  mode.
+- **Prompt v1.** Iterating the prompt is cheap — `PROMPT_VERSION` is bumped in
+  the script and recorded in every result row, so an A/B between prompt
+  versions is straightforward without losing the v1 baseline.
+
+## Cost report (TBD)
+
+<!-- report_auto.md §"Spend" block goes here. -->
+
+| Model | Audio min sent | Estimated $ | Actual $ |
+|-------|---------------:|------------:|---------:|
+| `gemini-2.5-pro` | TBD | TBD | TBD |
+| `gpt-4o-audio-preview` | TBD | TBD | TBD |
+| **Total** | — | TBD | TBD |
+
+Hard cap was `SYNTHBANSHEE_LLM_SPIKE_BUDGET_USD = $5.00`. Actual spend
+within budget: TBD.