test(terminal): pin the two unpinned arms of the Git Bash capacity gate

Gate-level ablation of the six-clause capacity condition found the six
conjuncts each individually pinned, but two neighbouring arms free:

- the `session.deps.onPaneProcessDied` presence check. The callback is
  optional on PaneConnectionDeps; without the guard a capacity exit calls
  `undefined` and throws out of the exit handler, leaving the pane neither
  retained nor torn down.
- the per-PTY keying in `noteTerminalInputForPty`. A generation installs its
  exit state when its callbacks are captured, before the transport rebinds
  its PTY id; a write in that window would be credited to the incoming PTY
  and silently suppress its capacity overlay.

Both new tests fail with their own arm reverted and pass with it restored.
No production change.

src/renderer/src/components/terminal-pane/pty-connection-git-bash-console-capacity.test.ts

@@ -461,6 +461,48 @@ describe('Git Bash console-capacity pane retention (STA-5604)', () => {
     expect(started.deps.onPaneProcessDied).not.toHaveBeenCalled()
   })
 
+  it('tears the pane down when the host wired no process-died handler', async () => {
+    // Why: `onPaneProcessDied` is optional on PaneConnectionDeps. Without the
+    // presence check the capacity branch would call `undefined` and abort the exit
+    // handler mid-teardown, leaving the pane neither retained nor closed.
+    const started = await startPane({
+      paneCount: 2,
+      deps: {
+        onPaneProcessDied: undefined,
+        paneTransportsRef: { current: new Map([[2, createMockTransport('pty-pane-2')]]) }
+      }
+    })
+
+    started.spawn('tab-pty')
+    started.emitOutput(CAPACITY_OUTPUT)
+    started.exit('tab-pty', 1)
+
+    expect(started.manager.closePane).toHaveBeenCalledWith(1)
+  })
+
+  it('keys an in-flight write to the PTY bound at the time, not the incoming generation', async () => {
+    // Why: a new stream generation installs its exit state when its callbacks are
+    // captured, which is BEFORE the transport rebinds its PTY id. A write landing in
+    // that window belongs to the outgoing PTY; crediting it to the incoming one would
+    // make a newborn shell look typed-into and silently drop its capacity overlay.
+    const { installPtyExitHibernate } = await import('./pty-connection/pty-exit-hibernate')
+    const session = { paneStartup: { command: 'zsh' } } as never as Parameters<
+      typeof installPtyExitHibernate
+    >[0]
+    installPtyExitHibernate(session)
+
+    const outgoing = session.currentProcessExitState
+    session.bindProcessExitState('outgoing-pty')
+    // The incoming generation's state is installed before its PTY id is bound.
+    const incoming = session.createProcessExitState({ command: 'zsh' })
+    session.currentProcessExitState = incoming
+
+    session.noteTerminalInputForPty('outgoing-pty')
+
+    expect(outgoing.userInteracted).toBe(true)
+    expect(incoming.userInteracted).toBe(false)
+  })
+
   it('keeps a freshly split Windows pane visible when its newborn PTY hits the console ceiling', async () => {
     const startup = { command: 'codex' }
     const started = await startPane({