Order the notes cache by sequence, not by who resolves last

One gesture puts two requests in flight. With the tab already loaded, clicking
the dock toggle while the textarea has focus fires `blur` -> `saveNote` and the
dock's mount -> `list_notes` in the same tick. The save finishes and its re-read
writes the post-save list; the mount's read -- issued earlier, still out -- then
lands its pre-save snapshot on top, and both panels show stale text until
something else refreshes.

`mutationChains` could not have caught this: it orders a project's writes
against each other and the mount load is a read outside it. Putting the read on
the chain would work, but it buys correctness with latency the user feels -- a
panel mount waiting behind `save_note`'s double-fsync write -- and leaves a
"mutation chain" holding reads.

The two requests are not competing for a resource; the loser's result is simply
older. So every write into `notesByProject[p]` now claims a per-project sequence
when the request behind it is issued, and `commitNotes` drops one whose sequence
predates what is already cached. Reads take their sequence at issue time, since
being ordered by resolution is the bug. Local patches -- the filter behind a
confirmed delete, the prepend behind a failed re-read -- take a fresh one at
commit time, because they are authoritative then rather than derived from an
earlier read, and anything still in flight behind them is genuinely stale. A
failed read commits under its *own* sequence, not a fresh one, so its empty list
cannot beat a later read that has the real answer.

`isCurrent()` stays, and is not folded in. It guards `setSaveState`, not the
cache: it asks whether this *panel* is still showing the project a save was made
for, which a per-project counter cannot answer -- two panels on one project share
every sequence value. Ordering and panel identity are two questions.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HjL1E2JFNctUqCYotUwqqb

app/src/hooks/useNotes.test.ts

@@ -369,4 +369,78 @@ describe("useNotes", () => {
     expect(dock.result.current.loading).toBe(false);
     expect(dock.result.current.notes).toHaveLength(1);
   });
+
+  it("does not let a slow mount read overwrite a fresher post-save refresh", async () => {
+    // One gesture, two requests. The tab is already loaded; the user clicks the
+    // dock toggle with the textarea focused, so `blur` → `saveNote` and the
+    // dock's mount → `list_notes` are issued in the same tick. The save's
+    // re-read writes the post-save list; the mount's read — issued earlier,
+    // still in flight — must not then land its pre-save snapshot on top of it.
+    const files = fakeBackend({ p1: [note({ body: "before" })] });
+    const tab = renderHook(() => useNotes("p1"));
+    await waitFor(() => expect(tab.result.current.loading).toBe(false));
+    expect(tab.result.current.notes[0].body).toBe("before");
+
+    // The dock's mount read: it snapshots the list as it is *now* (pre-save)
+    // and hangs, standing in for a plain read that is slower than
+    // `save_note`'s double-fsync write plus the re-read behind it.
+    let releaseMountRead: (() => void) | undefined;
+    listNotes.mockImplementationOnce(async (p: string) => {
+      const preSave = [...(files[p] ?? [])];
+      await new Promise<void>((resolve) => {
+        releaseMountRead = resolve;
+      });
+      return preSave;
+    });
+    const dock = renderHook(() => useNotes("p1"));
+    expect(releaseMountRead).toBeDefined();
+
+    // The save and its re-read complete while that read is still out.
+    await act(async () => {
+      await tab.result.current.saveNote(note({ body: "after" }));
+    });
+    expect(tab.result.current.notes[0].body).toBe("after");
+
+    // Now the stale read lands.
+    await act(async () => {
+      releaseMountRead!();
+      await Promise.resolve();
+    });
+
+    expect(tab.result.current.notes[0].body).toBe("after");
+    expect(dock.result.current.notes[0].body).toBe("after");
+  });
+
+  it("does not let a slow mount read resurrect a note deleted while it was in flight", async () => {
+    // The other half of the same ordering rule: a confirmed delete is newer
+    // than any read issued before it finished, so the read's pre-delete list
+    // must not be written back over the shortened one.
+    const files = fakeBackend({ p1: [note()] });
+    const tab = renderHook(() => useNotes("p1"));
+    await waitFor(() => expect(tab.result.current.loading).toBe(false));
+
+    let releaseMountRead: (() => void) | undefined;
+    listNotes.mockImplementationOnce(async (p: string) => {
+      const preDelete = [...(files[p] ?? [])];
+      await new Promise<void>((resolve) => {
+        releaseMountRead = resolve;
+      });
+      return preDelete;
+    });
+    const dock = renderHook(() => useNotes("p1"));
+    expect(releaseMountRead).toBeDefined();
+
+    await act(async () => {
+      await tab.result.current.deleteNote("n1");
+    });
+    expect(tab.result.current.notes).toHaveLength(0);
+
+    await act(async () => {
+      releaseMountRead!();
+      await Promise.resolve();
+    });
+
+    expect(tab.result.current.notes).toHaveLength(0);
+    expect(dock.result.current.notes).toHaveLength(0);
+  });
 });