Filter exact music identities before lexical and semantic candidate limits

crates/searchi-core/README.md

@@ -136,3 +136,15 @@ opens. The measured Windows synthetic fixture grew from about 295 MiB to 605 MiB
 - OCR, media extraction, and real model inference belong to subsequent modules.
 - Linux/macOS measurements, realistic mixed-document corpora, cold startup,
   memory budgets, and indexing performance remain unverified.
+
+### Exact music identities
+
+`SearchOptions.media_artist` and `media_title` constrain every retrieval lane to
+complete genuine probe fields, with Unicode simple lowercase and outer whitespace
+normalization. Both fields combine with AND; substring inference and full Unicode
+case folding are not claimed. Each request field accepts 1–1024 UTF-8 bytes.
+An empty query with either constraint returns bounded filename/path-ordered matches.
+Missing tags and legacy flattened-only records are ineligible, rather than admitting
+semantic neighbours. A normal media probe refresh populates the structured keys.
+Oversized genuine fields remain keyword-searchable but receive no truncated exact
+identity key. Guarded publication and same-stat event hints preserve invalidation.