fix(canvas): persist deletions immediately to prevent resurrection

Destructive operations (forget, delete, remember) now flush to
IndexedDB + localStorage immediately instead of using 2s debounce,
preventing deleted items from reappearing on page reload.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/community-sync.ts

@@ -699,7 +699,7 @@ export class CommunitySync extends EventTarget {
 		this.dispatchEvent(new CustomEvent("shape-state-changed", {
 			detail: { shapeId, state: 'forgotten', data: this.#doc.shapes?.[shapeId] }
 		}));
-		this.#scheduleSave();
+		this.#saveImmediate();
 		this.#syncToServer();
 	}
 
@@ -734,7 +734,7 @@ export class CommunitySync extends EventTarget {
 		this.dispatchEvent(new CustomEvent("shape-state-changed", {
 			detail: { shapeId, state: 'present', data: this.#doc.shapes?.[shapeId] }
 		}));
-		this.#scheduleSave();
+		this.#saveImmediate();
 		this.#syncToServer();
 	}
 
@@ -756,7 +756,7 @@ export class CommunitySync extends EventTarget {
 		this.dispatchEvent(new CustomEvent("shape-state-changed", {
 			detail: { shapeId, state: 'deleted', data: this.#doc.shapes?.[shapeId] }
 		}));
-		this.#scheduleSave();
+		this.#saveImmediate();
 		this.#syncToServer();
 	}
 
@@ -1013,6 +1013,18 @@ export class CommunitySync extends EventTarget {
 		}, 2000);
 	}
 
+	/** Flush doc to IndexedDB immediately (no debounce). Use for destructive ops. */
+	#saveImmediate(): void {
+		if (!this.#offlineStore) return;
+		if (this.#saveDebounceTimer) {
+			clearTimeout(this.#saveDebounceTimer);
+			this.#saveDebounceTimer = null;
+		}
+		const binary = Automerge.save(this.#doc);
+		this.#offlineStore.saveDocImmediate(this.#communitySlug, binary);
+		this.#offlineStore.saveDocEmergency(this.#communitySlug, binary);
+	}
+
 	#persistSyncState(): void {
 		if (!this.#offlineStore) return;