Freeze mixed-file retrieval diagnostic and shared-engine evaluator

tools/mixed-eval/README.md

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+# Mixed retrieval evaluator
+
+`evaluate.py` verifies the frozen labels and every asset, copies only those
+assets into an owned temporary corpus, and indexes it with the actual CLI.
+Semantic indexing uses the real shared service and explicit Google worker/model
+and CPU FFmpeg paths. Querying uses the same public read-only MCP search tool
+that local agents use. Lexical and hybrid modes are reported separately; code
+queries compare All files against Code scope. A semantic fallback is an error,
+not a lexical result mislabeled as model evidence. Model files are not downloaded.
+
+```powershell
+$env:SEARCHI_FORCE_CPU = '1'
+python tools/mixed-eval/evaluate.py --verify-only
+python -m unittest discover -s tools/mixed-eval -p 'test_*.py'
+python tools/mixed-eval/evaluate.py --cli target/release/searchi.exe --models .searchi/models/embeddinggemma2 --worker .searchi/runtime/auto/Release/searchi-gemma-worker.exe --ffmpeg .searchi/media-runtime/bin/ffmpeg.exe --ffprobe .searchi/media-runtime/bin/ffprobe.exe --output .searchi/qa/mixed-v1.json
+```
+
+Use actual absolute runtime paths for your platform if these development paths
+differ. Inference runs must be coordinated with other CPU measurements. Expect
+media indexing to take minutes; its explicit one-hour bound is a safety ceiling,
+not a performance target. Indexing and query errors remain visible. Temporary
+corpora/indexes are cleaned after the owned sessions close. Partial query results
+are retained in the requested output if a later request fails.
+
+Reported metrics are file-level top1, reciprocal rank and recall@5 after file
+identity deduplication. Hard negatives in the first five and no-answer queries
+returning any result are reported explicitly. This does **not** calibrate a
+rejection threshold. Timestamp labels are retained but scored only for file
+identity: use the separate media evaluator for segment localization. Unsupported
+temporal filters are recorded as skipped, never counted as passed.
+
+The raw report retains queries, expected IDs, ordered hits, source locations,
+scores, modes/scopes/languages and MCP roundtrip times. Those times exclude
+process/model initialization and do not represent native UI latency. Keep raw
+reports under ignored `.searchi`; review deliberate evidence before publishing.