fix(sidecar): panel button deletes the side chat instead of hiding it (#3961)

* fix(sidecar): make panel button delete the side chat instead of hiding it

The side chat panel's top-right button called `sidecar.close()`, which only
hid the panel — duplicating the header `SidecarTrigger` toggle. Repurpose the
button so the panel owns deletion and the header toggle owns hide/show.

- When a conversation exists, the button shows a trash icon and opens a
  confirmation dialog before deleting via `useDeleteThread` (backend cascade).
- In the draft state (references only, no thread yet) the header trigger is not
  rendered, so the button falls back to a plain close (X) that discards the
  draft without a confirm — there is nothing persisted to delete.

Also fix a latent double-delete bug surfaced by the new dialog:
`useDeleteThread` deletes through the LangGraph route (which drops the
thread_meta row) and then calls `deleteLocalThreadData`, which hits the same
gateway handler whose `require_existing=True` guard now 404s. Treat that 404 as
idempotent success. The recent-chat delete used fire-and-forget `mutate`, so it
swallowed this error; the sidecar's `mutateAsync` surfaced it as a toast.

The e2e mock now mirrors the gateway ownership guard (second DELETE 404s once
the thread is gone) so the regression stays covered. Adds tests for delete,
draft-state close, and header-owned hide/show.

* fix(sidecar): lock delete dialog while deletion is in flight

The delete confirmation dialog disabled Cancel during an in-flight
delete but still allowed dismissal via the overlay, Esc, and the
built-in close (X). Those paths could imply the delete was cancelled
when it was actually still running. Ignore dismissals and drop the
close button while `isDeleting` so only the (disabled) Cancel path
controls the dialog.

frontend/src/components/workspace/sidecar/sidecar-panel.tsx

@@ -8,6 +8,7 @@ import {
   MessageSquareTextIcon,
   PaperclipIcon,
   RocketIcon,
+  Trash2Icon,
   XIcon,
   ZapIcon,
 } from "lucide-react";
@@ -35,6 +36,14 @@ import {
   type PromptInputMessage,
 } from "@/components/ai-elements/prompt-input";
 import { Button } from "@/components/ui/button";
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog";
 import {
   DropdownMenuGroup,
   DropdownMenuLabel,
@@ -50,6 +59,7 @@ import {
 } from "@/core/sidecar";
 import { createSidecarThread } from "@/core/sidecar/api";
 import {
+  useDeleteThread,
   useThreadStream,
   type ThreadStreamOptions,
 } from "@/core/threads/hooks";
@@ -137,6 +147,9 @@ export function SidecarPanel({ className }: { className?: string }) {
   const { models, tokenUsageEnabled } = useModels();
   const [modelDialogOpen, setModelDialogOpen] = useState(false);
   const [creatingThread, setCreatingThread] = useState(false);
+  const [deleteDialogOpen, setDeleteDialogOpen] = useState(false);
+  const { mutateAsync: deleteThread, isPending: isDeleting } =
+    useDeleteThread();
   const [queuedSubmit, setQueuedSubmit] = useState<{
     message: PromptInputMessage;
     references: SidecarReference[];
@@ -437,6 +450,39 @@ export function SidecarPanel({ className }: { className?: string }) {
     ],
   );
 
+  const discardDraftAndClose = useCallback(() => {
+    sidecar.clearActiveReferences();
+    sidecar.setSidecarThreadId(null);
+    sidecar.close();
+  }, [sidecar]);
+
+  const handleDelete = useCallback(async () => {
+    const threadId = sidecar.sidecarThreadId;
+    // Guard: the trash button only opens this dialog once a thread exists, so a
+    // missing id here means the draft was cleared underneath us — just close.
+    if (!threadId) {
+      discardDraftAndClose();
+      setDeleteDialogOpen(false);
+      return;
+    }
+    try {
+      await deleteThread({ threadId });
+      discardDraftAndClose();
+      setDeleteDialogOpen(false);
+      toast.success(t.sidecar.deleteSuccess);
+    } catch (error) {
+      toast.error(
+        error instanceof Error ? error.message : t.sidecar.deleteFailed,
+      );
+    }
+  }, [
+    deleteThread,
+    discardDraftAndClose,
+    sidecar.sidecarThreadId,
+    t.sidecar.deleteFailed,
+    t.sidecar.deleteSuccess,
+  ]);
+
   return (
     <div
       className={cn("flex size-full min-h-0 flex-col", className)}
@@ -454,16 +500,35 @@ export function SidecarPanel({ className }: { className?: string }) {
                 : t.sidecar.noContext}
           </div>
         </div>
-        <Tooltip content={t.common.close}>
-          <Button
-            aria-label={t.common.close}
-            size="icon-sm"
-            variant="ghost"
-            onClick={() => sidecar.close()}
-          >
-            <XIcon />
-          </Button>
-        </Tooltip>
+        {hasSidecarThread ? (
+          <Tooltip content={t.sidecar.delete}>
+            <Button
+              aria-label={t.sidecar.delete}
+              className="text-muted-foreground hover:text-destructive"
+              data-testid="sidecar-delete-button"
+              size="icon-sm"
+              variant="ghost"
+              onClick={() => setDeleteDialogOpen(true)}
+            >
+              <Trash2Icon />
+            </Button>
+          </Tooltip>
+        ) : (
+          // No conversation yet — nothing to delete, so this just discards the
+          // draft and closes the panel. A plain X (no confirm) keeps it light.
+          <Tooltip content={t.common.close}>
+            <Button
+              aria-label={t.common.close}
+              className="text-muted-foreground hover:text-foreground"
+              data-testid="sidecar-close-button"
+              size="icon-sm"
+              variant="ghost"
+              onClick={() => discardDraftAndClose()}
+            >
+              <XIcon />
+            </Button>
+          </Tooltip>
+        )}
       </header>
 
       <div className="min-h-0 flex-1">
@@ -558,6 +623,55 @@ export function SidecarPanel({ className }: { className?: string }) {
           </PromptInput>
         </PromptInputProvider>
       </div>
+
+      <Dialog
+        open={deleteDialogOpen}
+        onOpenChange={(open) => {
+          // While the delete is in flight the only way out is the (disabled)
+          // Cancel button, so ignore overlay/Esc/close-button dismissals that
+          // would otherwise hide the dialog and imply the delete was cancelled.
+          if (!open && isDeleting) {
+            return;
+          }
+          setDeleteDialogOpen(open);
+        }}
+      >
+        <DialogContent
+          showCloseButton={!isDeleting}
+          onEscapeKeyDown={(event) => {
+            if (isDeleting) {
+              event.preventDefault();
+            }
+          }}
+          onInteractOutside={(event) => {
+            if (isDeleting) {
+              event.preventDefault();
+            }
+          }}
+        >
+          <DialogHeader>
+            <DialogTitle>{t.sidecar.delete}</DialogTitle>
+            <DialogDescription>{t.sidecar.deleteConfirm}</DialogDescription>
+          </DialogHeader>
+          <DialogFooter>
+            <Button
+              variant="outline"
+              onClick={() => setDeleteDialogOpen(false)}
+              disabled={isDeleting}
+            >
+              {t.common.cancel}
+            </Button>
+            <Button
+              variant="destructive"
+              data-testid="sidecar-delete-confirm-button"
+              onClick={() => void handleDelete()}
+              disabled={isDeleting}
+            >
+              {isDeleting ? t.common.loading : t.common.delete}
+            </Button>
+          </DialogFooter>
+        </DialogContent>
+      </Dialog>
     </div>
   );
 }

frontend/src/core/i18n/locales/en-US.ts

@@ -452,6 +452,11 @@ export const enUS: Translations = {
     title: "Side chat",
     open: "Open side chat",
     close: "Close side chat",
+    delete: "Delete side chat",
+    deleteConfirm:
+      "Are you sure you want to delete this side chat? This action cannot be undone. To simply hide it, use the side chat toggle in the header instead.",
+    deleteSuccess: "Side chat deleted",
+    deleteFailed: "Failed to delete side chat.",
     addToConversation: "Add to conversation",
     askInSideChat: "Ask in side chat",
     reference: "Reference",

frontend/src/core/i18n/locales/types.ts

@@ -362,6 +362,10 @@ export interface Translations {
     title: string;
     open: string;
     close: string;
+    delete: string;
+    deleteConfirm: string;
+    deleteSuccess: string;
+    deleteFailed: string;
     addToConversation: string;
     askInSideChat: string;
     reference: string;

frontend/src/core/i18n/locales/zh-CN.ts

@@ -436,6 +436,11 @@ export const zhCN: Translations = {
     title: "侧边对话",
     open: "打开侧边对话",
     close: "关闭侧边对话",
+    delete: "删除侧边对话",
+    deleteConfirm:
+      "确定要删除该侧边对话吗？此操作不可撤销。如果只是想隐藏，请使用顶部的侧边对话开关。",
+    deleteSuccess: "侧边对话已删除",
+    deleteFailed: "删除侧边对话失败。",
     addToConversation: "添加到对话",
     askInSideChat: "在侧边聊天中提问",
     reference: "引用",

frontend/src/core/threads/hooks.ts

@@ -2044,7 +2044,12 @@ async function deleteLocalThreadData(threadId: string) {
     },
   );
 
-  if (!response.ok) {
+  // A 404 means the thread is already gone — the desired end state. The prior
+  // `apiClient.threads.delete` call hits the same gateway handler (nginx
+  // rewrites /api/langgraph/threads/* to /api/threads/*) and removes the
+  // thread_meta row, so this second delete's ownership guard 404s. Treat it as
+  // success to keep the delete idempotent.
+  if (!response.ok && response.status !== 404) {
     const error = await response
       .json()
       .catch(() => ({ detail: "Failed to delete local thread data." }));

frontend/tests/e2e/sidecar-chat.spec.ts

@@ -781,6 +781,10 @@ test.describe("Side chat", () => {
     await expect(
       page.getByRole("heading", { name: "Ask a follow-up" }),
     ).toBeVisible();
+    // Draft state (no thread created yet): the header shows a plain close (X),
+    // not the destructive delete — there is nothing persisted to delete.
+    await expect(page.getByTestId("sidecar-close-button")).toBeVisible();
+    await expect(page.getByTestId("sidecar-delete-button")).toBeHidden();
     const sidecarReference = page.getByTestId("sidecar-reference-attachment");
     const sidecarInputForm = page.locator("form").filter({
       has: page.getByPlaceholder(/deeper follow-up/i),
@@ -943,14 +947,8 @@ test.describe("Side chat", () => {
     await expectComposerHeightsEqual(page);
     await expect(page.getByTestId("sidecar-header-trigger")).toBeVisible();
 
-    await page
-      .getByTestId("sidecar-panel")
-      .getByRole("button", { name: /close/i })
-      .click();
-    await expect(page.getByTestId("sidecar-panel")).toBeHidden();
-    await expect(page.getByTestId("sidecar-header-trigger")).toBeVisible();
-    await page.getByTestId("sidecar-header-trigger").click();
-    await expect(page.getByTestId("sidecar-panel")).toBeVisible();
+    // Hiding the side chat is owned by the header trigger; the panel's own
+    // button deletes the side chat instead of hiding it.
     await expect(
       page.getByTestId("sidecar-header-trigger"),
     ).toHaveAccessibleName("Close side chat");
@@ -1279,4 +1277,273 @@ test.describe("Side chat", () => {
       timeout: 10_000,
     });
   });
+
+  test("deletes the side chat from the panel's own button", async ({
+    page,
+  }) => {
+    mockLangGraphAPI(page, {
+      threads: [
+        {
+          thread_id: MOCK_THREAD_ID,
+          title: "Main conversation",
+          messages: [
+            {
+              type: "human",
+              id: "parent-human-1",
+              content: [{ type: "text", text: "Plan the feature." }],
+            },
+            {
+              type: "ai",
+              id: "parent-ai-1",
+              content: "Build it as a side conversation.",
+            },
+          ],
+        },
+        {
+          thread_id: MOCK_SIDECAR_THREAD_ID,
+          title: "Restored side chat",
+          updated_at: "2025-01-01T00:00:01Z",
+          metadata: {
+            deerflow_sidecar: true,
+            parent_thread_id: MOCK_THREAD_ID,
+            sidecar_context_type: "referenced_message",
+            sidecar_context_label: "Selected assistant text #2",
+            sidecar_context_count: 1,
+            referenced_message_id: "parent-ai-1",
+            referenced_message_ids: ["parent-ai-1"],
+            referenced_message_role: "assistant",
+            referenced_message_roles: ["assistant"],
+          },
+          messages: [
+            {
+              type: "ai",
+              id: "side-ai-1",
+              content: "Restored side answer.",
+            },
+          ],
+        },
+      ],
+    });
+
+    await page.goto(`/workspace/chats/${MOCK_THREAD_ID}`);
+    await expect(
+      page.getByText("Build it as a side conversation."),
+    ).toBeVisible({ timeout: 15_000 });
+    await expect(page.getByTestId("sidecar-header-trigger")).toBeVisible({
+      timeout: 10_000,
+    });
+
+    // Open the side chat panel via the header trigger.
+    await page.getByTestId("sidecar-header-trigger").click();
+    await expect(page.getByTestId("sidecar-panel")).toBeVisible();
+
+    // The panel's own button deletes the side chat (it does not merely hide it).
+    await page.getByTestId("sidecar-delete-button").click();
+    await expect(
+      page.getByText("This action cannot be undone", { exact: false }),
+    ).toBeVisible();
+
+    const deleteRequestPromise = page.waitForRequest(
+      (request) =>
+        request.method() === "DELETE" &&
+        request.url().includes(`/threads/${MOCK_SIDECAR_THREAD_ID}`),
+    );
+    await page.getByTestId("sidecar-delete-confirm-button").click();
+    await deleteRequestPromise;
+
+    // The panel closes and, because the sidecar thread is gone, the header
+    // trigger unmounts too — hiding is owned by the trigger, deleting by this.
+    await expect(page.getByTestId("sidecar-panel")).toBeHidden();
+    await expect(page.getByTestId("sidecar-header-trigger")).toBeHidden({
+      timeout: 10_000,
+    });
+  });
+
+  test("keeps the delete dialog open while the delete is in flight", async ({
+    page,
+  }) => {
+    mockLangGraphAPI(page, {
+      threads: [
+        {
+          thread_id: MOCK_THREAD_ID,
+          title: "Main conversation",
+          messages: [
+            {
+              type: "human",
+              id: "parent-human-1",
+              content: [{ type: "text", text: "Plan the feature." }],
+            },
+            {
+              type: "ai",
+              id: "parent-ai-1",
+              content: "Build it as a side conversation.",
+            },
+          ],
+        },
+        {
+          thread_id: MOCK_SIDECAR_THREAD_ID,
+          title: "Restored side chat",
+          updated_at: "2025-01-01T00:00:01Z",
+          metadata: {
+            deerflow_sidecar: true,
+            parent_thread_id: MOCK_THREAD_ID,
+            sidecar_context_type: "referenced_message",
+            sidecar_context_label: "Selected assistant text #2",
+            sidecar_context_count: 1,
+            referenced_message_id: "parent-ai-1",
+            referenced_message_ids: ["parent-ai-1"],
+            referenced_message_role: "assistant",
+            referenced_message_roles: ["assistant"],
+          },
+          messages: [
+            {
+              type: "ai",
+              id: "side-ai-1",
+              content: "Restored side answer.",
+            },
+          ],
+        },
+      ],
+    });
+
+    // Hold the local-delete step open so the mutation stays pending while we
+    // probe every dismissal path Radix would otherwise honor.
+    let releaseDelete: (() => void) | undefined;
+    const deleteGate = new Promise<void>((resolve) => {
+      releaseDelete = resolve;
+    });
+    await page.route(/\/api\/threads\/[^/]+$/, async (route) => {
+      if (route.request().method() !== "DELETE") {
+        return route.fallback();
+      }
+      await deleteGate;
+      return route.fallback();
+    });
+
+    await page.goto(`/workspace/chats/${MOCK_THREAD_ID}`);
+    await expect(
+      page.getByText("Build it as a side conversation."),
+    ).toBeVisible({ timeout: 15_000 });
+    await expect(page.getByTestId("sidecar-header-trigger")).toBeVisible({
+      timeout: 10_000,
+    });
+
+    await page.getByTestId("sidecar-header-trigger").click();
+    await expect(page.getByTestId("sidecar-panel")).toBeVisible();
+
+    await page.getByTestId("sidecar-delete-button").click();
+    const dialogTitle = page.getByRole("heading", { name: "Delete side chat" });
+    await expect(dialogTitle).toBeVisible();
+    // The built-in Radix close (X) is present before the delete starts.
+    await expect(
+      page.locator('[data-slot="dialog-content"] [data-slot="dialog-close"]'),
+    ).toHaveCount(1);
+
+    await page.getByTestId("sidecar-delete-confirm-button").click();
+
+    // Delete is in flight: confirm shows the loading label and Cancel disables.
+    await expect(
+      page.getByTestId("sidecar-delete-confirm-button"),
+    ).toBeDisabled();
+    await expect(page.getByRole("button", { name: "Cancel" })).toBeDisabled();
+    // The built-in close (X) is removed so it can't imply a cancel.
+    await expect(
+      page.locator('[data-slot="dialog-content"] [data-slot="dialog-close"]'),
+    ).toHaveCount(0);
+
+    // Esc and overlay clicks must not dismiss the dialog mid-delete.
+    await page.keyboard.press("Escape");
+    await expect(dialogTitle).toBeVisible();
+    await page
+      .locator('[data-slot="dialog-overlay"]')
+      .click({ position: { x: 5, y: 5 } });
+    await expect(dialogTitle).toBeVisible();
+
+    // Once the delete resolves the dialog closes and the panel goes away.
+    releaseDelete?.();
+    await expect(dialogTitle).toBeHidden({ timeout: 10_000 });
+    await expect(page.getByTestId("sidecar-panel")).toBeHidden();
+  });
+
+  test("closes the draft side chat without deleting when no conversation exists", async ({
+    page,
+  }) => {
+    mockLangGraphAPI(page, {
+      threads: [
+        {
+          thread_id: MOCK_THREAD_ID,
+          title: "Main conversation",
+          messages: [
+            {
+              type: "human",
+              id: "parent-human-1",
+              content: [{ type: "text", text: "Plan the feature." }],
+            },
+            {
+              type: "ai",
+              id: "parent-ai-1",
+              content: "Build it as a side conversation.",
+            },
+          ],
+        },
+      ],
+    });
+    await page.route("**/api/models", (route) => {
+      if (route.request().method() !== "GET") {
+        return route.fallback();
+      }
+      return route.fulfill({
+        status: 200,
+        contentType: "application/json",
+        body: JSON.stringify({
+          models: [
+            {
+              id: "deepseek-v4-pro",
+              name: "deepseek-v4-pro",
+              model: "deepseek-v4-pro",
+              display_name: "DeepSeek V4 Pro",
+              supports_thinking: true,
+              supports_reasoning_effort: true,
+            },
+          ],
+          token_usage: { enabled: false },
+        }),
+      });
+    });
+
+    let deleteRequestFired = false;
+    page.on("request", (request) => {
+      if (
+        request.method() === "DELETE" &&
+        request.url().includes("/threads/")
+      ) {
+        deleteRequestFired = true;
+      }
+    });
+
+    await page.goto(`/workspace/chats/${MOCK_THREAD_ID}`);
+    await expect(
+      page.getByText("Build it as a side conversation."),
+    ).toBeVisible({ timeout: 15_000 });
+
+    // Open the side chat as a draft (references only, no thread created yet).
+    await selectTextAndClickToolbarButton(
+      page,
+      "Build it as a side conversation.",
+      "Ask in side chat",
+    );
+    await expect(page.getByTestId("sidecar-panel")).toBeVisible();
+    await expect(
+      page.getByTestId("sidecar-reference-attachment"),
+    ).toBeVisible();
+
+    // The draft has no persisted thread, so the header offers a plain close (X)
+    // instead of the destructive delete button.
+    await expect(page.getByTestId("sidecar-delete-button")).toBeHidden();
+    await page.getByTestId("sidecar-close-button").click();
+
+    await expect(page.getByTestId("sidecar-panel")).toBeHidden();
+    // No thread was ever created, so closing must not issue a DELETE request.
+    expect(deleteRequestFired).toBe(false);
+  });
 });

frontend/tests/e2e/utils/mock-api.ts

@@ -691,6 +691,22 @@ export function mockLangGraphAPI(page: Page, options?: MockAPIOptions) {
 
   void page.route(/\/api\/threads\/[^/]+$/, (route) => {
     if (route.request().method() === "DELETE") {
+      const threadId = decodeURIComponent(
+        new URL(route.request().url()).pathname.split("/").at(-1) ?? "",
+      );
+      // Mirror the gateway's `require_existing=True` ownership guard: deleting
+      // an already-removed thread 404s. `useDeleteThread` first deletes via the
+      // LangGraph route (which drops the thread_meta row) and then hits this
+      // route, so this reproduces the real double-delete 404 the frontend must
+      // treat as idempotent success.
+      if (!threads.some((thread) => thread.thread_id === threadId)) {
+        return route.fulfill({
+          status: 404,
+          contentType: "application/json",
+          body: JSON.stringify({ detail: `Thread ${threadId} not found` }),
+        });
+      }
+      threads = threads.filter((thread) => thread.thread_id !== threadId);
       return route.fulfill({
         status: 204,
       });