Freeze separate music metadata field diagnostic

tools/media-eval/README.md

@@ -60,3 +60,21 @@ positives are explicitly ineligible, filters remain explicitly unsupported, and
 all unfiltered negatives remain visible without abstention. Existing queries are
 diagnostics rather than new held-out evidence. Unseen music with missing and
 misleading tags needs independently frozen validation before deployment.
+
+`music_fields` is the subsequent diagnostic hypothesis: individual whitelisted
+fields use the neutral document title `File metadata` and a shared 2048-byte
+budget. It reuses per-query audio maxima verbatim from the exact preserved v1
+report (SHA-256 checked), avoiding duplicate audio inference. All queries and
+negatives remain; scores for every field are retained, with no threshold/weights.
+
+```powershell
+cargo test --manifest-path tools/media-eval/Cargo.toml --bin music_fields --locked
+cargo run --manifest-path tools/media-eval/Cargo.toml --bin music_fields --locked -- prepare .searchi/qa/music-metadata-v1-results.json .searchi/qa/music-fields-v2-plan.json
+$env:SEARCHI_FORCE_CPU = '1'
+cargo run --manifest-path tools/media-eval/Cargo.toml --bin music_fields --locked -- run fixtures/media .searchi/qa/music-metadata-v1-results.json .searchi/qa/music-fields-v2-plan.json .searchi/models/embeddinggemma2 .searchi/runtime/auto/Release/searchi-gemma-worker.exe .searchi/qa/music-fields-v2-results.json
+```
+
+Prepare before inference, preserve the plan hash, and use fresh output paths.
+Runtime/worker and source hashes must match v1. This diagnostic intentionally
+depends on its exact baseline and remains a known-pool hypothesis comparison;
+it is not a general production scorer or new independent validation.