libraries: surface globals, normalise excluded_dirs on write

Two follow-ups to the PATCH endpoint:

1. GET /libraries now returns ``global_excluded_dirs`` alongside the
   library list — the union-with-globals semantics is invisible from
   the per-library row alone, and the admin UI needs to show what's
   already being skipped before the operator adds entries that would
   duplicate.

2. PATCH /libraries/{id} canonicalises the excluded_dirs string on
   write via the new ``normalize_excluded_dirs_input``: trims per
   entry, drops empties, dedupes preserving first-occurrence order,
   comma-joins without inner whitespace. Empty / whitespace-only →
   NULL. Round-trip stable so re-saving an entry produces an
   identical row.

Five new tests cover the empty / whitespace, trim, dedup, round-trip,
and overlap-with-globals cases. effective_excluded_dirs continues to
keep overlapping entries between globals and per-library on purpose —
PathExcluder accepts repeats and there's no behavioural reason to
dedupe at merge time.

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

src/libraries.rs

@@ -82,7 +82,9 @@ impl Library {
 
 /// Parse a comma-separated excluded_dirs column into a Vec, dropping
 /// empty entries (mirrors `AppState::parse_excluded_dirs` for the env
-/// var). NULL → empty Vec.
+/// var). NULL → empty Vec. Duplicates are preserved — `PathExcluder`
+/// accepts repeats, and the storage-side normaliser is where dedup
+/// happens.
 pub fn parse_excluded_dirs_column(raw: Option<&str>) -> Vec<String> {
     match raw {
         None => Vec::new(),
@@ -95,6 +97,32 @@ pub fn parse_excluded_dirs_column(raw: Option<&str>) -> Vec<String> {
     }
 }
 
+/// Canonicalise an excluded_dirs string for storage: parse → trim →
+/// dedupe (preserving insertion order) → comma-join with no inner
+/// whitespace. Empty / whitespace-only input → `None` (writes NULL).
+///
+/// Used by `PATCH /libraries/{id}` so two users typing the same entries
+/// in different orders / casings / whitespace land on the same stored
+/// form, and a typo'd duplicate (`@eaDir, @eaDir`) collapses on save.
+/// Round-trip stable: writing the output back through this function
+/// yields the same string.
+pub fn normalize_excluded_dirs_input(raw: &str) -> Option<String> {
+    let parsed = parse_excluded_dirs_column(Some(raw));
+    if parsed.is_empty() {
+        return None;
+    }
+    let mut seen = std::collections::HashSet::new();
+    let deduped: Vec<String> = parsed
+        .into_iter()
+        .filter(|s| seen.insert(s.clone()))
+        .collect();
+    if deduped.is_empty() {
+        None
+    } else {
+        Some(deduped.join(","))
+    }
+}
+
 impl From<LibraryRow> for Library {
     fn from(row: LibraryRow) -> Self {
         Library {
@@ -335,6 +363,13 @@ pub struct LibraryStatus {
 #[derive(serde::Serialize)]
 pub struct LibrariesResponse {
     pub libraries: Vec<LibraryStatus>,
+    /// Globally-excluded paths/patterns from the `EXCLUDED_DIRS` env var.
+    /// Applied **in union** with each library's own `excluded_dirs`. Surfaced
+    /// here so an admin UI can show the operator "you already skip these
+    /// everywhere" before they add per-library entries that would duplicate
+    /// the global list. Read-only — globals live in `.env` and aren't
+    /// mutable via the API today.
+    pub global_excluded_dirs: Vec<String>,
 }
 
 #[get("/libraries")]
@@ -361,7 +396,10 @@ pub async fn list_libraries(_claims: Claims, app_state: Data<AppState>) -> impl
                 .unwrap_or(LibraryHealth::Online),
         })
         .collect();
-    HttpResponse::Ok().json(LibrariesResponse { libraries })
+    HttpResponse::Ok().json(LibrariesResponse {
+        libraries,
+        global_excluded_dirs: app_state.excluded_dirs.clone(),
+    })
 }
 
 /// Body for PATCH /libraries/{id}. Both fields are optional — omitting
@@ -416,15 +454,12 @@ pub async fn patch_library(
         }
     }
     if let Some(raw) = body.excluded_dirs.as_deref() {
-        let trimmed = raw.trim();
+        // Canonicalise on write — trim, dedupe, drop empties — so the DB
-        // Empty / whitespace-only → NULL so the column reads back the
+        // stores a round-trip-stable form regardless of how messy the
-        // same way a never-set library does (parse_excluded_dirs_column
+        // user typed it. Empty / whitespace-only → NULL (matches a
-        // returns Vec::new() for NULL).
+        // never-set library, parse_excluded_dirs_column returns []).
-        let stored: Option<&str> = if trimmed.is_empty() {
+        let normalised = normalize_excluded_dirs_input(raw);
-            None
+        let stored: Option<&str> = normalised.as_deref();
-        } else {
-            Some(trimmed)
-        };
         match diesel::update(libraries::table.filter(libraries::id.eq(lib_id)))
             .set(libraries::excluded_dirs.eq(stored))
             .execute(&mut conn)
@@ -637,6 +672,78 @@ mod tests {
         assert_eq!(combined.len(), 3);
     }
 
+    #[test]
+    fn effective_excluded_dirs_keeps_overlap_between_global_and_per_library() {
+        // Two sources both excluding `@eaDir` is legal — `PathExcluder`
+        // accepts repeats, and there's no behavioral reason to dedupe
+        // here. Documents the design choice so a future refactor that
+        // tightens this is forced to update both code and tests.
+        let globals = vec!["@eaDir".to_string()];
+        let lib = Library {
+            id: 1,
+            name: "main".into(),
+            root_path: "/x".into(),
+            enabled: true,
+            excluded_dirs: vec!["@eaDir".to_string(), "/private".to_string()],
+        };
+        let combined = lib.effective_excluded_dirs(&globals);
+        // 2 occurrences of @eaDir + /private = 3 entries total.
+        assert_eq!(combined, vec!["@eaDir", "@eaDir", "/private"]);
+    }
+
+    #[test]
+    fn normalize_excluded_dirs_input_handles_empty_and_whitespace() {
+        assert_eq!(normalize_excluded_dirs_input(""), None);
+        assert_eq!(normalize_excluded_dirs_input("   "), None);
+        assert_eq!(normalize_excluded_dirs_input(",,,"), None);
+        assert_eq!(normalize_excluded_dirs_input(" , , "), None);
+    }
+
+    #[test]
+    fn normalize_excluded_dirs_input_trims_per_entry() {
+        // Inner whitespace stripped on each item, comma-joined without
+        // spaces. Mirrors how parse_excluded_dirs_column reads it back.
+        assert_eq!(
+            normalize_excluded_dirs_input(" @eaDir , /private , .thumbnails "),
+            Some("@eaDir,/private,.thumbnails".to_string())
+        );
+    }
+
+    #[test]
+    fn normalize_excluded_dirs_input_dedupes_preserving_first_occurrence() {
+        // Exact-string duplicates collapse; the first occurrence wins
+        // (preserves the operator's typed order so they recognise their
+        // intent on round-trip).
+        assert_eq!(
+            normalize_excluded_dirs_input("@eaDir, /private, @eaDir, /private"),
+            Some("@eaDir,/private".to_string())
+        );
+        // Whitespace-distinct entries collapse to the same canonical
+        // form. Case is preserved — `Foo` and `foo` are different keys
+        // (filesystem case-sensitivity is platform-dependent; we don't
+        // make that call here).
+        assert_eq!(
+            normalize_excluded_dirs_input(" Foo,foo, Foo "),
+            Some("Foo,foo".to_string())
+        );
+    }
+
+    #[test]
+    fn normalize_excluded_dirs_input_is_round_trip_stable() {
+        // Writing the normaliser's output back through it yields the
+        // same string. PATCH-clearing edits round-trip cleanly through
+        // parse_excluded_dirs_column too.
+        let raw = " /a/b ,, /a/b , c ";
+        let once = normalize_excluded_dirs_input(raw).expect("not empty");
+        let twice = normalize_excluded_dirs_input(&once).expect("not empty");
+        assert_eq!(once, twice);
+        // Parsing the stored form back gives the deduped Vec.
+        assert_eq!(
+            parse_excluded_dirs_column(Some(&once)),
+            vec!["/a/b".to_string(), "c".to_string()]
+        );
+    }
+
     fn probe_lib(id: i32, root: String) -> Library {
         Library {
             id,