fix(frontend/copilot): close artifact panel on copilot page unmount

The artifact panel lived in the Zustand store, so its `isOpen` state survived
copilot page unmounts. Navigating to /profile, /home, or a new chat and
coming back would re-render the panel open with the prior session's
artifact. Tickets SECRT-2254, SECRT-2223, SECRT-2220 all trace to this.

Reset the panel in a useAutoOpenArtifacts unmount cleanup so leaving the
copilot page (or session-less limbo) always returns users to a clean
default-closed panel. Session-change reset was already handled; this covers
the nav-away → nav-back case.

Two new failing-first tests drive it:
- SECRT-2254 repro: open panel → unmount hook → panel must be closed.
- SECRT-2220 repro: seed store with a stale `isOpen: true`, mount+unmount,
  remount → panel must be closed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

autogpt_platform/frontend/src/app/(platform)/copilot/components/ChatContainer/useAutoOpenArtifacts.test.ts

@@ -88,4 +88,53 @@ describe("useAutoOpenArtifacts", () => {
     expect(s.activeArtifact?.id).toBe("c");
     expect(s.history).toEqual([]);
   });
+
+  // SECRT-2254: "had agent panel open then went to profile then went to home
+  // and agent panel was still open". Nav-away unmounts the copilot page; if
+  // the panel state persists in the store, coming back re-renders it open.
+  it("closes the panel on unmount so nav-away → nav-back doesn't resurrect it (SECRT-2254)", () => {
+    useCopilotUIStore.getState().openArtifact(makeArtifact(A_ID, "a.txt"));
+    expect(useCopilotUIStore.getState().artifactPanel.isOpen).toBe(true);
+
+    const { unmount } = renderHook(() =>
+      useAutoOpenArtifacts({ sessionId: "s1" }),
+    );
+
+    act(() => {
+      unmount();
+    });
+
+    const s = useCopilotUIStore.getState().artifactPanel;
+    expect(s.isOpen).toBe(false);
+    expect(s.activeArtifact).toBeNull();
+    expect(s.history).toEqual([]);
+  });
+
+  // SECRT-2220: "keep closed by default" — a fresh mount (e.g. user returns to
+  // /copilot) must start with a closed panel even if the store somehow carries
+  // stale state from a prior life.
+  it("does not re-open a panel whose store state is stale on fresh mount (SECRT-2220)", () => {
+    // Simulate the store being left in an open state by a previous page life.
+    useCopilotUIStore.setState({
+      artifactPanel: {
+        isOpen: true,
+        isMinimized: false,
+        isMaximized: false,
+        width: 600,
+        activeArtifact: makeArtifact(A_ID, "stale.txt"),
+        history: [],
+      },
+    });
+
+    const { unmount } = renderHook(() =>
+      useAutoOpenArtifacts({ sessionId: "s1" }),
+    );
+    act(() => {
+      unmount();
+    });
+
+    // Next mount of the page should see a clean store.
+    renderHook(() => useAutoOpenArtifacts({ sessionId: "s1" }));
+    expect(useCopilotUIStore.getState().artifactPanel.isOpen).toBe(false);
+  });
 });

autogpt_platform/frontend/src/app/(platform)/copilot/components/ChatContainer/useAutoOpenArtifacts.ts

@@ -26,4 +26,13 @@ export function useAutoOpenArtifacts({
       resetArtifactPanel();
     }
   }, [sessionId, resetArtifactPanel]);
+
+  // Reset on unmount so navigating away from /copilot (to /profile, /home,
+  // etc.) can't leave the panel open in the Zustand store, which would then
+  // render the panel re-open when the user returns. See SECRT-2254/2220.
+  useEffect(() => {
+    return () => {
+      resetArtifactPanel();
+    };
+  }, [resetArtifactPanel]);
 }