fix(maestro): mobile drawer access, focus preservation, stale rAF focus (#140)

Three more fixes from acceptance review:

- structured.ts's header omitted the .sessions-btn attach.ts's terminal
  header carries. The sidebar is off-canvas on mobile, so a structured
  session had no way to reach it — add the same button and
  requestToggleDrawer wiring.

- ConnectionPool.reconcileViews always remounted a repaired connection
  with focus:false. If the mistyped pane was the one actually focused,
  disposing it dropped DOM focus while `focusedId` still named it. Pass
  `focus: this.focusedId === id` instead — `focusedId` only ever names a
  real focus (multiview.ts skips setFocus while previewing), so a
  preview or a merely-visible split neighbour still comes back
  unfocused.

- onMount's deferred requestAnimationFrame focus had no way to tell it
  had been superseded by an unmount (or a remount elsewhere) before it
  fired, so a parked pane could steal focus a frame later. A token
  bumped on every mount/unmount lets the callback recognize it's stale
  and no-op.

Regression tests: 7 new (structured.test.ts, connections.test.ts). 495
tests total.

web/src/connections.test.ts

@@ -9,6 +9,7 @@ import type { Session } from "./types.js";
 // the pool reaches the focused connection with them.
 const sent: { id: string; data: string }[] = [];
 const disposed: string[] = [];
+const mounts: { id: string; focus: boolean | undefined }[] = [];
 function fakeConn(kind: string, id: string) {
   const el = document.createElement("div");
   el.dataset.kind = kind;
@@ -17,7 +18,9 @@ function fakeConn(kind: string, id: string) {
     sessionId: id,
     kind,
     el,
-    onMount() {},
+    onMount(opts?: { focus?: boolean }) {
+      mounts.push({ id, focus: opts?.focus });
+    },
     onUnmount() {},
     focusTerminal() {},
     sendInput(data: string) {
@@ -39,6 +42,7 @@ afterEach(() => {
   vi.unstubAllGlobals();
   sent.length = 0;
   disposed.length = 0;
+  mounts.length = 0;
 });
 
 /** Minimal fixture for the `CatalogState` a `CatalogStore` broadcasts. */
@@ -256,4 +260,52 @@ describe("ConnectionPool: view resolution races", () => {
 
     expect(disposed).toEqual([]);
   });
+
+  it("re-focuses the fresh connection when the replaced pane was the focused session", () => {
+    mockFetch();
+    const { store, socket } = fakeStore();
+    const pool = new ConnectionPool({ store });
+    const pane = document.createElement("div");
+    pool.mount(A, pane);
+    pool.setFocus(A);
+    mounts.length = 0;
+
+    socket.push([session(A, "Structured")]);
+
+    expect(disposed).toEqual(["attach:" + A]);
+    expect(mounts).toEqual([{ id: A, focus: true }]);
+  });
+
+  it("does not steal focus for a merely-visible pane that was never actually focused", () => {
+    mockFetch();
+    const { store, socket } = fakeStore();
+    const pool = new ConnectionPool({ store });
+    const paneA = document.createElement("div");
+    const paneB = document.createElement("div");
+    pool.mount(A, paneA);
+    pool.mount(B, paneB);
+    pool.setFocus(B); // B is the real keyboard focus; A is only visible
+    mounts.length = 0;
+
+    socket.push([session(A, "Structured")]);
+
+    expect(disposed).toEqual(["attach:" + A]);
+    expect(mounts).toEqual([{ id: A, focus: false }]);
+  });
+
+  it("does not focus a parked (unmounted) connection it repairs", () => {
+    mockFetch();
+    const { store, socket } = fakeStore();
+    const pool = new ConnectionPool({ store });
+    const pane = document.createElement("div");
+    pool.mount(A, pane);
+    pool.setFocus(A);
+    pool.unmount(A); // parked — no longer visible, `focusedId` still names it
+    mounts.length = 0;
+
+    socket.push([session(A, "Structured")]);
+
+    expect(disposed).toEqual(["attach:" + A]);
+    expect(mounts).toEqual([]); // parked repair calls onUnmount, never onMount
+  });
 });