fix(app): keep the browser attachment and tab menu reliable

packages/app/src/session/browser/model.ts

@@ -42,10 +42,24 @@ export function createSessionBrowser(session: SessionModel) {
     const owner = session.ownership.capture()
     const target = { sessionID, endpoint: server.conn.http }
     let registration: BrowserPaneRegistration | undefined
+    let retry: ReturnType<typeof setTimeout> | undefined
+    let attempts = 0
     const register = () => {
       if (registration) return
       registration = pane.register(target, (event) =>
-        owner.run(() => (event.type === "open" ? open() : setState({ browser: event.state, error: event.error }))),
+        owner.run(() => {
+          if (event.type === "open") return open()
+          // The desktop dropped the attachment (server restart, attach race).
+          // Re-register so the agent's browser tool comes back without a reload.
+          if (event.error === "browser.pane.registration.closed") {
+            registration?.close()
+            registration = undefined
+            setState({ registration: undefined, browser: null, error: undefined })
+            retry = setTimeout(register, Math.min(30_000, 1_000 * 2 ** attempts++))
+            return
+          }
+          setState({ browser: event.state, error: event.error })
+        }),
       )
       setState({ registration, browser: null, error: undefined })
     }
@@ -56,6 +70,7 @@ export function createSessionBrowser(session: SessionModel) {
     if (!session.shared.data.session.creating(sessionID)) register()
     onCleanup(() => {
       unsubscribe()
+      clearTimeout(retry)
       registration?.close()
     })
   })

packages/app/src/session/files/session-side-panel.tsx

@@ -442,6 +442,9 @@ export function SessionSidePanel(props: {
                                   variant="ghost-muted"
                                   size="large"
                                   aria-label={language.t("session.tab.add")}
+                                  // The tablist redirects focus entering it to the selected
+                                  // tab, which counts as focus-outside and closes the menu.
+                                  onPointerDown={(event: PointerEvent) => event.preventDefault()}
                                 />
                                 <Menu.Portal>
                                   <Menu.Content>

packages/desktop/src/renderer/platform/index.ts

@@ -39,6 +39,8 @@ export function createDesktopPlatform(
           if (!closed && value.bindingID === bindingID) onEvent(value.event)
         })
         const ready = api.browserPane.request({ type: "register", bindingID, target })
+        // Failures reach the owner through the closed-state event; keep the bare promise handled.
+        void ready.catch(() => undefined)
         return {
           setLayout(layout) {
             if (!closed)