feat(offline_cache): add maintenance module for bulk delete and redownload selection

Pure logic, no Tauri state. remove_album_cached_tracks bundles the
SQLite delete with on-disk CMAF cleanup. select_redownload_targets
enforces the rule that re-download skips in-flight Downloading tracks
and optionally restricts to Failed only.

cc

src-tauri/src/offline_cache/maintenance.rs

@@ -0,0 +1,109 @@
+//! Maintenance operations on the offline cache: bulk delete and re-download.
+//! Pure logic — no Tauri state. Callable from any future TUI or headless binary.
+
+use std::path::Path;
+
+use super::cmaf_store::BundleLayout;
+use super::{CachedTrackInfo, OfflineCacheDb, OfflineCacheStatus};
+
+#[derive(Debug, Clone)]
+pub struct AlbumRemovalReport {
+    pub album_id: String,
+    pub removed_track_ids: Vec<u64>,
+    pub freed_bytes: u64,
+}
+
+/// Removes all cached tracks of an album: SQLite rows + on-disk CMAF bundles.
+/// Filesystem errors per-track are logged and not propagated; SQLite is the
+/// source of truth and the bundle directories are best-effort cleanup.
+pub fn remove_album_cached_tracks(
+    db: &OfflineCacheDb,
+    offline_root: &Path,
+    album_id: &str,
+) -> Result<AlbumRemovalReport, String> {
+    let (ids, bytes) = db.delete_album_tracks(album_id)?;
+    for &track_id in &ids {
+        let layout = BundleLayout::new(offline_root, track_id);
+        if layout.track_dir.exists() {
+            if let Err(e) = std::fs::remove_dir_all(&layout.track_dir) {
+                log::warn!(
+                    "Failed to remove CMAF dir for track {}: {} (continuing)",
+                    track_id,
+                    e
+                );
+            }
+        }
+    }
+    Ok(AlbumRemovalReport {
+        album_id: album_id.to_string(),
+        removed_track_ids: ids,
+        freed_bytes: bytes,
+    })
+}
+
+/// Filters tracks targeted by re-download: skip in-flight Downloading,
+/// optionally restrict to Failed only.
+pub fn select_redownload_targets(
+    tracks: &[CachedTrackInfo],
+    failed_only: bool,
+) -> Vec<&CachedTrackInfo> {
+    tracks
+        .iter()
+        .filter(|track| match track.status {
+            OfflineCacheStatus::Downloading => false,
+            OfflineCacheStatus::Failed => true,
+            _ => !failed_only,
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::offline_cache::OfflineCacheStatus;
+
+    fn track_with_status(id: u64, status: OfflineCacheStatus) -> CachedTrackInfo {
+        CachedTrackInfo {
+            track_id: id,
+            title: format!("t{}", id),
+            artist: "A".into(),
+            album: None,
+            album_id: None,
+            duration_secs: 0,
+            file_size_bytes: 0,
+            quality: "lossless".into(),
+            bit_depth: None,
+            sample_rate: None,
+            status,
+            progress_percent: 0,
+            error_message: None,
+            created_at: "".into(),
+            last_accessed_at: "".into(),
+        }
+    }
+
+    #[test]
+    fn redownload_targets_full_skips_only_downloading() {
+        let tracks = vec![
+            track_with_status(1, OfflineCacheStatus::Ready),
+            track_with_status(2, OfflineCacheStatus::Downloading),
+            track_with_status(3, OfflineCacheStatus::Failed),
+            track_with_status(4, OfflineCacheStatus::Queued),
+        ];
+        let picked = select_redownload_targets(&tracks, false);
+        let ids: Vec<u64> = picked.iter().map(|track| track.track_id).collect();
+        assert_eq!(ids, vec![1, 3, 4]);
+    }
+
+    #[test]
+    fn redownload_targets_failed_only_returns_failed() {
+        let tracks = vec![
+            track_with_status(1, OfflineCacheStatus::Ready),
+            track_with_status(2, OfflineCacheStatus::Failed),
+            track_with_status(3, OfflineCacheStatus::Downloading),
+        ];
+        let picked = select_redownload_targets(&tracks, true);
+        let ids: Vec<u64> = picked.iter().map(|track| track.track_id).collect();
+        assert_eq!(ids, vec![2]);
+    }
+}

src-tauri/src/offline_cache/mod.rs

@@ -9,6 +9,7 @@
 pub mod cmaf_store;
 pub mod db;
 pub mod downloader;
+pub mod maintenance;
 pub mod metadata;
 pub mod migration;
 pub mod path_validator;