test(storage): pin FTS5 contract for search_transcripts

search_transcripts already backs onto the transcripts_fts virtual table
(migration v4, trigger-maintained) via MATCH + ORDER BY rank. Adding a
test to lock the behaviour: token matching is case-insensitive, rank-
ordered, and non-matching tokens return nothing. This is Phase G of the
post-OpenWhispr audit — semantic embeddings stay deferred until the FTS
experience actually hits a wall.

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

crates/storage/src/database.rs

@@ -888,6 +888,61 @@ mod tests {
         assert!(deleted.is_none());
     }
 
+    #[tokio::test]
+    async fn search_transcripts_uses_fts5_and_ranks_by_relevance() {
+        // Locks in the FTS5 behaviour contract: MATCH-based substring-like
+        // search (case-insensitive tokens) with rank-ordered results, so
+        // anyone swapping `search_transcripts` out for embeddings later
+        // knows what invariants they must preserve.
+        let pool = test_pool().await;
+
+        let rows = [
+            ("t1", "The Parakeet speech model runs on sherpa-onnx."),
+            (
+                "t2",
+                "Parakeet parakeet parakeet dominates English benchmarks.",
+            ),
+            ("t3", "Whisper large-v3 remains the multilingual champion."),
+        ];
+
+        for (id, text) in rows {
+            insert_transcript(
+                &pool,
+                &InsertTranscriptParams {
+                    id,
+                    text,
+                    source: "microphone",
+                    profile_id: crate::DEFAULT_PROFILE_ID,
+                    title: None,
+                    audio_path: None,
+                    duration: 1.0,
+                    engine: Some("whisper"),
+                    model_id: Some("whisper-tiny-en"),
+                    inference_ms: None,
+                    sample_rate: None,
+                    audio_channels: None,
+                    format_mode: None,
+                    remove_fillers: false,
+                    british_english: false,
+                    anti_hallucination: false,
+                },
+            )
+            .await
+            .unwrap();
+        }
+
+        let hits = search_transcripts(&pool, "parakeet", 10).await.unwrap();
+        let ids: Vec<&str> = hits.iter().map(|row| row.id.as_str()).collect();
+        assert_eq!(
+            ids,
+            vec!["t2", "t1"],
+            "t3 has no 'parakeet' token; t2 outranks t1 on repetition"
+        );
+
+        let no_match = search_transcripts(&pool, "moonshine", 10).await.unwrap();
+        assert!(no_match.is_empty());
+    }
+
     #[tokio::test]
     async fn task_crud_roundtrip() {
         let pool = test_pool().await;