fix(ssh): two overlapping bridged-terminal attaches hand back the viewer they replace (#30856)

* fix(ssh): two overlapping bridged attaches hand back the viewer they replace

Co-authored-by: Claude <noreply@anthropic.com>

* fix(ssh): the newest bridged attach keeps its viewer even when an older one answers last

Co-authored-by: Claude <noreply@anthropic.com>

* fix(ssh): an older bridged connect still paints its screen when a newer attach keeps the viewer

Co-authored-by: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/renderer/src/components/terminal-pane/legacy-relay-bridge-transport.test.ts

@@ -387,6 +387,48 @@ describe('a runtime pane bridged to an older relay’s terminal', () => {
     ).toEqual(['ssh:ssh-box@@pty-3'])
   })
 
+  it('hands back every viewer when two attaches for the pane overlap', async () => {
+    let next = 0
+    bridge.attach.mockImplementation(async () => {
+      next += 1
+      return { status: 'attached', replay: '', acquisitionId: next }
+    })
+    const transport = createLegacyRelayBridgeTransport(PTY, innerTransport())
+    // A connect and an attach for the same pane, both answered before either settles.
+    const connecting = transport.connect({ url: '', sessionId: PTY, callbacks: callbacks() })
+    transport.attach({ existingPtyId: PTY, callbacks: callbacks() })
+    await connecting
+    await vi.waitFor(() => expect(bridge.attach).toHaveBeenCalledTimes(2))
+    await Promise.resolve()
+    transport.detach?.()
+    expect(bridge.detach.mock.calls.map(([args]) => args.acquisitionId).sort()).toEqual([1, 2])
+  })
+
+  it('keeps the newest attach’s viewer when an older attach answers last', async () => {
+    const answers: ((acquisitionId: number) => void)[] = []
+    bridge.attach.mockImplementation(
+      () =>
+        new Promise((resolve) =>
+          answers.push((acquisitionId) =>
+            resolve({ status: 'attached', replay: `SCREEN-${acquisitionId}`, acquisitionId })
+          )
+        )
+    )
+    const transport = createLegacyRelayBridgeTransport(PTY, innerTransport())
+    const older = transport.connect({ url: '', sessionId: PTY, callbacks: callbacks() })
+    transport.attach({ existingPtyId: PTY, callbacks: callbacks() })
+    await vi.waitFor(() => expect(answers).toHaveLength(2))
+    // The newer attach answers first, then the older one.
+    answers[1](2)
+    await vi.waitFor(() => expect(transport.isConnected()).toBe(true))
+    answers[0](1)
+    // The connect still paints its screen: the attach that won delivers none of its own.
+    await expect(older).resolves.toMatchObject({ replay: 'SCREEN-1' })
+    expect(bridge.detach.mock.calls.map(([args]) => args.acquisitionId)).toEqual([1])
+    transport.detach?.()
+    expect(bridge.detach.mock.calls.map(([args]) => args.acquisitionId)).toEqual([1, 2])
+  })
+
   it('hands any other connect straight to the managed server’s transport', async () => {
     const inner = innerTransport()
     const transport = createLegacyRelayBridgeTransport(PTY, inner)

src/renderer/src/components/terminal-pane/legacy-relay-bridge-transport.ts

@@ -42,6 +42,23 @@ export function createLegacyRelayBridgeTransport(ptyId: string, inner: PtyTransp
     viewer = null
   }
 
+  /** Issue order of this pane's attaches, and which one the held viewer came from. */
+  const seqs = { issued: 0, viewer: 0 }
+
+  // Overlapping attaches (connect, attach, reattach) each get a viewer; the newest issued keeps
+  // its own, whichever answers last, and every other one is handed back.
+  const adoptViewer = (seq: number, acquisitionId: number): void => {
+    if (seq < seqs.viewer) {
+      api?.detach({ ptyId, acquisitionId })
+      return
+    }
+    if (viewer !== null && viewer !== acquisitionId) {
+      api?.detach({ ptyId, acquisitionId: viewer })
+    }
+    viewer = acquisitionId
+    seqs.viewer = seq
+  }
+
   const release = (): void => {
     epoch += 1
     unsubscribe.forEach((dispose) => dispose())
@@ -85,6 +102,7 @@ export function createLegacyRelayBridgeTransport(ptyId: string, inner: PtyTransp
     }
     reattaching = true
     const at = epoch
+    const seq = ++seqs.issued
     try {
       // The screen comes through onReplay in output order: applied from this reply instead, its
       // clear would erase output the relay printed after it.
@@ -93,7 +111,7 @@ export function createLegacyRelayBridgeTransport(ptyId: string, inner: PtyTransp
         return
       }
       if (result.status === 'attached') {
-        viewer = result.acquisitionId
+        adoptViewer(seq, result.acquisitionId)
         clearUnreachable()
       } else if (result.status === 'exited' || result.status === 'not-bridged') {
         clearUnreachable()
@@ -168,6 +186,7 @@ export function createLegacyRelayBridgeTransport(ptyId: string, inner: PtyTransp
     mode = 'bridge'
     subscribe()
     const at = epoch
+    const seq = ++seqs.issued
     const result = await api.attach({ ptyId })
     if (!stillWanted(at, result)) {
       return undefined
@@ -184,7 +203,7 @@ export function createLegacyRelayBridgeTransport(ptyId: string, inner: PtyTransp
       showUnreachable()
       return { id: ptyId, isReattach: true, replay: '' }
     }
-    viewer = result.acquisitionId
+    adoptViewer(seq, result.acquisitionId)
     return { id: ptyId, isReattach: true, replay: result.replay }
   }