fix: harden frontend — toggle race guard, fresh debounce snapshot, error surfacing

Add toggling guard to TaskItem preventing double-toggle from rapid clicks
or swipes. Fix debounced save in TaskDetailView to read task at timeout
time instead of capturing a stale snapshot at call time. Remove unused
_unlistenFs variable. Surface reorder_task and watch_workspace errors
instead of silently swallowing them.

apps/tauri/src/lib/components/TaskDetailView.svelte

@@ -34,9 +34,8 @@
 
   function debouncedSave(fields: Partial<Task>) {
     clearTimeout(saveTimer);
-    const snapshot = { ...task };
     saveTimer = setTimeout(() => {
-      app.updateTask({ ...snapshot, ...fields, updated_at: new Date().toISOString() });
+      app.updateTask({ ...task, ...fields, updated_at: new Date().toISOString() });
     }, 400);
   }
 

apps/tauri/src/lib/components/TaskItem.svelte

@@ -19,6 +19,7 @@
 
   let isCompleted = $derived(task.status === "completed");
   let justChecked = $state(false);
+  let toggling = $state(false);
 
   $effect(() => {
     const _ = task.status;
@@ -35,6 +36,8 @@
 
   async function handleToggle(e: MouseEvent) {
     e.stopPropagation();
+    if (toggling) return;
+    toggling = true;
     justChecked = true;
     await new Promise((r) => setTimeout(r, 300));
     transitioning = true;
@@ -42,6 +45,7 @@
     await new Promise((r) => setTimeout(r, 200));
     justChecked = false;
     await app.toggleTask(task.id);
+    toggling = false;
   }
 
   function handleTouchStart(e: TouchEvent) {
@@ -57,14 +61,15 @@
   }
 
   function handleTouchEnd() {
-    if (Math.abs(swipeX) > 100) {
+    if (Math.abs(swipeX) > 100 && !toggling) {
       swipeX = 0;
       swiping = false;
+      toggling = true;
       justChecked = true;
       setTimeout(() => {
         transitioning = true;
         animateInIds.add(task.id);
-        setTimeout(() => { justChecked = false; app.toggleTask(task.id); }, 200);
+        setTimeout(() => { justChecked = false; app.toggleTask(task.id).finally(() => { toggling = false; }); }, 200);
       }, 300);
       return;
     }

apps/tauri/src/lib/stores/app.svelte.ts

@@ -9,12 +9,8 @@ import type {
 } from "../types";
 
 // Listen for file system changes from the backend watcher.
-// Store the unlisten function so it can be cleaned up if needed.
-let _unlistenFs: (() => void) | null = null;
 listen("fs-changed", () => {
   loadLists();
-}).then((unlisten) => {
-  _unlistenFs = unlisten;
 });
 
 // ── Reactive state ───────────────────────────────────────────────────
@@ -98,7 +94,7 @@ async function switchWorkspace(name: string) {
     activeListId = null;
     await loadLists();
     const ws = config?.workspaces[name];
-    if (ws) invoke("watch_workspace", { path: ws.path }).catch(() => {});
+    if (ws) invoke("watch_workspace", { path: ws.path }).catch((e) => console.warn("File watcher failed:", e));
     error = null;
   } catch (e) {
     error = String(e);
@@ -200,7 +196,7 @@ async function toggleTask(taskId: string) {
     // Move to top of list locally, then persist order in background
     if (updated.status === "backlog") {
       tasks = [updated, ...tasks.filter((t) => t.id !== taskId)];
-      invoke("reorder_task", { listId: activeListId, taskId, newPosition: 0 }).catch(() => {});
+      invoke("reorder_task", { listId: activeListId, taskId, newPosition: 0 }).catch((e) => { error = String(e); });
     } else {
       tasks = tasks.map((t) => (t.id === taskId ? updated : t));
     }