Clear pending input when attaching a different remote terminal handle

When switching between different remote terminal handles, debounced input
meant for the previous terminal could get incorrectly flushed and sent
to the newly attached terminal.

Fix this by clearing the batcher's pending state (text and byte counts)
and invoking `inputBatcher.clear()` if the attached terminal handle
changes.

src/renderer/src/components/terminal-pane/remote-runtime-pty-batching.ts

@@ -50,6 +50,8 @@ export function createRemoteRuntimePtyTextBatcher(
 
   const clear = (): void => {
     clearTimer()
+    pending = ''
+    pendingBytes = 0
     validationVersion += 1
     validationTail = null
   }

src/renderer/src/components/terminal-pane/remote-runtime-pty-transport.test.ts

@@ -342,6 +342,50 @@ describe('createRemoteRuntimePtyTransport', () => {
     expect(transport.isConnected()).toBe(false)
   })
 
+  it('drops pending input when attaching a different remote terminal handle', async () => {
+    vi.useFakeTimers()
+    runtimeSubscribe.mockImplementation(
+      async (_args: unknown, callbacks: typeof subscriptionCallbacks) => {
+        subscriptionCallbacks = callbacks
+        return { unsubscribe: vi.fn(), sendBinary: subscriptionSendBinary }
+      }
+    )
+    try {
+      const { createRemoteRuntimePtyTransport } = await import('./remote-runtime-pty-transport')
+      const transport = createRemoteRuntimePtyTransport('env-1', {
+        worktreeId: 'wt-1',
+        tabId: 'tab-1',
+        leafId: 'pane:1'
+      })
+
+      transport.attach({
+        existingPtyId: 'remote:env-1@@terminal-old',
+        cols: 80,
+        rows: 24,
+        callbacks: {}
+      })
+      expect(transport.sendInput('queued-for-old')).toBe(true)
+
+      transport.attach({
+        existingPtyId: 'remote:env-1@@terminal-new',
+        cols: 80,
+        rows: 24,
+        callbacks: {}
+      })
+      runtimeCall.mockClear()
+
+      await vi.advanceTimersByTimeAsync(10)
+
+      expect(runtimeCall).not.toHaveBeenCalledWith(
+        expect.objectContaining({
+          method: 'terminal.send'
+        })
+      )
+    } finally {
+      vi.useRealTimers()
+    }
+  })
+
   it('ignores stale attach subscription rejection after reattaching a newer remote terminal', async () => {
     let rejectOldSubscription: ((error: Error) => void) | null = null
     const newStream = {

src/renderer/src/components/terminal-pane/remote-runtime-pty-transport.ts

@@ -507,7 +507,13 @@ export function createRemoteRuntimePtyTransport(
       storedCallbacks = options.callbacks
       currentRuntimeEnvironmentId =
         getRemoteRuntimePtyEnvironmentId(options.existingPtyId) ?? runtimeEnvironmentId
-      handle = getRemoteRuntimeTerminalHandle(options.existingPtyId)
+      const previousHandle = handle
+      const nextHandle = getRemoteRuntimeTerminalHandle(options.existingPtyId)
+      if (previousHandle && previousHandle !== nextHandle) {
+        // Why: debounced input is scoped by the current terminal handle at flush time.
+        inputBatcher.clear()
+      }
+      handle = nextHandle
       if (!handle) {
         connected = false
         remotePtyId = null