fix: replace O(n²) duplicate detection with map-based O(1) lookups

Replace linear scan deduplication of snapshot IDs in RemoveAllSnapshots()
and PruneBlobs() with map[string]bool for O(1) lookups.

Previously, each new snapshot ID was checked against the entire collected
slice via a linear scan, resulting in O(n²) overall complexity. Now a
'seen' map provides constant-time membership checks while preserving
insertion order in the slice.

closes #12

internal/database/schema.sql

@@ -103,7 +103,7 @@ CREATE TABLE IF NOT EXISTS snapshot_files (
     file_id TEXT NOT NULL,
     PRIMARY KEY (snapshot_id, file_id),
     FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
-    FOREIGN KEY (file_id) REFERENCES files(id)
+    FOREIGN KEY (file_id) REFERENCES files(id) ON DELETE CASCADE
 );
 
 -- Index for efficient file lookups (used in orphan detection)
@@ -116,7 +116,7 @@ CREATE TABLE IF NOT EXISTS snapshot_blobs (
     blob_hash TEXT NOT NULL,
     PRIMARY KEY (snapshot_id, blob_id),
     FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE,
-    FOREIGN KEY (blob_id) REFERENCES blobs(id)
+    FOREIGN KEY (blob_id) REFERENCES blobs(id) ON DELETE CASCADE
 );
 
 -- Index for efficient blob lookups (used in orphan detection)
@@ -130,7 +130,7 @@ CREATE TABLE IF NOT EXISTS uploads (
     size INTEGER NOT NULL,
     duration_ms INTEGER NOT NULL,
     FOREIGN KEY (blob_hash) REFERENCES blobs(blob_hash),
-    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id)
+    FOREIGN KEY (snapshot_id) REFERENCES snapshots(id) ON DELETE CASCADE
 );
 
 -- Index for efficient snapshot lookups

internal/vaultik/snapshot.go

@@ -419,7 +419,7 @@ func (v *Vaultik) listRemoteSnapshotIDs() (map[string]bool, error) {
 	return remoteSnapshots, nil
 }
 
-// reconcileLocalWithRemote removes local snapshots not in remote and returns the surviving local map
+// reconcileLocalWithRemote builds a map of local snapshots keyed by ID for cross-referencing with remote
 func (v *Vaultik) reconcileLocalWithRemote(remoteSnapshots map[string]bool) (map[string]*database.Snapshot, error) {
 	localSnapshots, err := v.Repositories.Snapshots.ListRecent(v.ctx, 10000)
 	if err != nil {
@@ -431,19 +431,6 @@ func (v *Vaultik) reconcileLocalWithRemote(remoteSnapshots map[string]bool) (map
 		localSnapshotMap[s.ID.String()] = s
 	}
 
-	for _, snap := range localSnapshots {
-		snapshotIDStr := snap.ID.String()
-		if !remoteSnapshots[snapshotIDStr] {
-			log.Info("Removing local snapshot not found in remote", "snapshot_id", snap.ID)
-			if err := v.deleteSnapshotFromLocalDB(snapshotIDStr); err != nil {
-				log.Error("Failed to delete local snapshot", "snapshot_id", snap.ID, "error", err)
-			} else {
-				log.Info("Deleted local snapshot not found in remote", "snapshot_id", snap.ID)
-				delete(localSnapshotMap, snapshotIDStr)
-			}
-		}
-	}
-
 	return localSnapshotMap, nil
 }
 
@@ -872,7 +859,7 @@ func (v *Vaultik) syncWithRemote() error {
 		snapshotIDStr := snapshot.ID.String()
 		if !remoteSnapshots[snapshotIDStr] {
 			log.Info("Removing local snapshot not found in remote", "snapshot_id", snapshot.ID)
-			if err := v.Repositories.Snapshots.Delete(v.ctx, snapshotIDStr); err != nil {
+			if err := v.deleteSnapshotFromLocalDB(snapshotIDStr); err != nil {
 				log.Error("Failed to delete local snapshot", "snapshot_id", snapshot.ID, "error", err)
 			} else {
 				removedCount++
@@ -1001,6 +988,7 @@ func (v *Vaultik) listAllRemoteSnapshotIDs() ([]string, error) {
 	log.Info("Listing all snapshots")
 	objectCh := v.Storage.ListStream(v.ctx, "metadata/")
 
+	seen := make(map[string]bool)
 	var snapshotIDs []string
 	for object := range objectCh {
 		if object.Err != nil {
@@ -1015,14 +1003,8 @@ func (v *Vaultik) listAllRemoteSnapshotIDs() ([]string, error) {
 			}
 			if strings.HasSuffix(object.Key, "/") || strings.Contains(object.Key, "/manifest.json.zst") {
 				sid := parts[1]
-				found := false
-				for _, id := range snapshotIDs {
-					if id == sid {
-						found = true
-						break
-					}
-				}
-				if !found {
+				if !seen[sid] {
+					seen[sid] = true
 					snapshotIDs = append(snapshotIDs, sid)
 				}
 			}