test: cover resolve_library_param and per-library ExifDao filter

Adds 9 unit tests around the library plumbing:
- resolve_library_param branches (absent, empty/whitespace, numeric id,
  name, unknown id, unknown name)
- Library::resolve symmetry with strip_root
- ExifDao::get_all_with_date_taken in union and scoped modes

Introduces SqliteExifDao::from_connection test constructor mirroring the
existing preview_dao pattern so DAO tests can drive an in-memory SQLite.

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

src/libraries.rs

@@ -198,4 +198,85 @@ mod tests {
         let outside = lib.strip_root(Path::new("/etc/passwd"));
         assert!(outside.is_none());
     }
+
+    #[test]
+    fn library_resolve_joins_under_root() {
+        let lib = Library {
+            id: 1,
+            name: "main".into(),
+            root_path: "/tmp/media".into(),
+        };
+        let abs = lib.resolve("2024/photo.jpg");
+        assert_eq!(abs, PathBuf::from("/tmp/media/2024/photo.jpg"));
+    }
+
+    fn state_with_libraries(libs: Vec<Library>) -> AppState {
+        let mut state = AppState::test_state();
+        state.libraries = libs;
+        state
+    }
+
+    fn sample_libraries() -> Vec<Library> {
+        vec![
+            Library {
+                id: 1,
+                name: "main".into(),
+                root_path: "/tmp/main".into(),
+            },
+            Library {
+                id: 7,
+                name: "archive".into(),
+                root_path: "/tmp/archive".into(),
+            },
+        ]
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_absent_is_union() {
+        let state = state_with_libraries(sample_libraries());
+        assert!(matches!(resolve_library_param(&state, None), Ok(None)));
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_empty_or_whitespace_is_union() {
+        let state = state_with_libraries(sample_libraries());
+        assert!(matches!(resolve_library_param(&state, Some("")), Ok(None)));
+        assert!(matches!(
+            resolve_library_param(&state, Some("   ")),
+            Ok(None)
+        ));
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_numeric_id_matches() {
+        let state = state_with_libraries(sample_libraries());
+        let lib = resolve_library_param(&state, Some("7"))
+            .expect("valid id")
+            .expect("some library");
+        assert_eq!(lib.id, 7);
+        assert_eq!(lib.name, "archive");
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_name_matches() {
+        let state = state_with_libraries(sample_libraries());
+        let lib = resolve_library_param(&state, Some("main"))
+            .expect("valid name")
+            .expect("some library");
+        assert_eq!(lib.id, 1);
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_unknown_id_errs() {
+        let state = state_with_libraries(sample_libraries());
+        let err = resolve_library_param(&state, Some("999")).unwrap_err();
+        assert!(err.contains("unknown library id"));
+    }
+
+    #[actix_rt::test]
+    async fn resolve_library_param_unknown_name_errs() {
+        let state = state_with_libraries(sample_libraries());
+        let err = resolve_library_param(&state, Some("missing")).unwrap_err();
+        assert!(err.contains("unknown library name"));
+    }
 }