fix(web): disable archive on running threads and fix misleading failure toast

Macroscope and Cursor Bugbot flagged two real issues in the single-thread
archive path (sidebar row menu and chat header menu): the menu item stayed
enabled while a thread had an active turn, so it always failed against
archiveThread's ThreadArchiveBlockedError guard, and any failure after a
successful archive (e.g. the post-archive navigation to a new thread) was
reported as "Failed to archive thread" even though the thread had already
been archived. Both are already handled correctly in the bulk-archive path
(buildMultiSelectThreadContextMenuItems disables on hasRunningThread, and
archiveSelectedThreadEntries distinguishes a post-archive navigation
failure); this brings the single-thread path in line with that pattern.

Author: lnieuwenhuis

apps/web/src/components/Sidebar.tsx

@@ -2964,6 +2964,8 @@ export default function Sidebar() {
               isSnoozed,
               canSnoozeNow: canSnooze(thread, { now: new Date().toISOString() }),
               isRegeneratingTitle,
+              isRunning:
+                thread.session?.status === "running" && thread.session.activeTurnId != null,
               supports: {
                 settlement: supportsSettlement,
                 snooze: supportsSnooze,
@@ -3074,13 +3076,20 @@ export default function Sidebar() {
               );
               if (confirmed._tag === "Failure" || !confirmed.value) return;
             }
-            const result = await archiveThread(threadRef);
+            let didArchive = false;
+            const result = await archiveThread(threadRef, {
+              onArchived: () => {
+                didArchive = true;
+              },
+            });
             if (result._tag === "Failure" && !isAtomCommandInterrupted(result)) {
               const error = squashAtomCommandFailure(result);
               toastManager.add(
                 stackedThreadToast({
                   type: "error",
-                  title: "Failed to archive thread",
+                  title: didArchive
+                    ? "Thread archived, but navigation failed"
+                    : "Failed to archive thread",
                   description: error instanceof Error ? error.message : "An error occurred.",
                 }),
               );

apps/web/src/components/threadActionMenu.logic.test.ts

@@ -9,6 +9,7 @@ const baseState: ThreadActionMenuState = {
   isSnoozed: false,
   canSnoozeNow: true,
   isRegeneratingTitle: false,
+  isRunning: false,
   supports: { settlement: true, snooze: true, pinning: true, titleRegeneration: true },
   snoozePresets: [
     { id: "hour", label: "In 1 hour", whenLabel: "3:00 PM", snoozedUntil: "2026-08-07T15:00:00Z" },
@@ -80,4 +81,11 @@ describe("buildThreadActionMenuItems", () => {
       }),
     ).toContain("archive");
   });
+
+  it("disables archive while the thread is running", () => {
+    const archiveItem = buildThreadActionMenuItems({ ...baseState, isRunning: true }).find(
+      (item) => item.id === "archive",
+    );
+    expect(archiveItem?.disabled).toBe(true);
+  });
 });

apps/web/src/components/threadActionMenu.logic.ts

@@ -31,6 +31,8 @@ export interface ThreadActionMenuState {
   readonly isSnoozed: boolean;
   readonly canSnoozeNow: boolean;
   readonly isRegeneratingTitle: boolean;
+  /** Archive rejects a thread with an active turn, so disable it here rather than let the action fail. */
+  readonly isRunning: boolean;
   readonly supports: {
     readonly settlement: boolean;
     readonly snooze: boolean;
@@ -108,7 +110,7 @@ export function buildThreadActionMenuItems(
     // (stays visible in the Settled shelf) and Delete (clears history for
     // good), so it sits beside Delete without borrowing its destructive
     // styling.
-    { id: "archive", label: "Archive thread" },
+    { id: "archive", label: "Archive thread", disabled: state.isRunning },
     { id: "delete", label: "Delete", destructive: true, icon: "trash" },
   ];
 }

apps/web/src/hooks/useThreadActionMenu.ts

@@ -139,6 +139,7 @@ export function useThreadActionMenu(input: {
           isSnoozed: supports.snooze && effectiveSnoozed(thread, { now: now.toISOString() }),
           canSnoozeNow: canSnooze(thread, { now: now.toISOString() }),
           isRegeneratingTitle,
+          isRunning: thread.session?.status === "running" && thread.session.activeTurnId != null,
           supports,
           snoozePresets,
         });
@@ -260,7 +261,18 @@ export function useThreadActionMenu(input: {
               );
               if (confirmed._tag === "Failure" || !confirmed.value) return;
             }
-            await reportFailure("Failed to archive thread", () => archiveThread(threadRef));
+            let didArchive = false;
+            const result = await archiveThread(threadRef, {
+              onArchived: () => {
+                didArchive = true;
+              },
+            });
+            if (result._tag === "Failure" && !isAtomCommandInterrupted(result)) {
+              failureToast(
+                didArchive ? "Thread archived, but navigation failed" : "Failed to archive thread",
+                squashAtomCommandFailure(result),
+              );
+            }
             return;
           }
           case "delete": {