fix(ssh): a Disconnect or Remove during a background connect sticks (#29918)

A background connect (managed tunnel, census, runtime context) that was
waiting for the old transport to close resumed after the user's
Disconnect or Remove host and registered a fresh connection. Re-check the
attempt token after that await so the cancelled attempt never registers.

src/main/ssh/ssh-connection-manager.test.ts

@@ -169,6 +169,30 @@ describe('SshConnectionManager', () => {
     expect(manager.getConnection(target.id)).toBe(replacement)
   })
 
+  it('keeps a Disconnect that lands while a background connect closes the old transport', async () => {
+    const manager = new SshConnectionManager({ onStateChange: vi.fn() })
+    await manager.connect(target)
+    const old = mockState.instances[0]
+    // The pooled transport dropped, so a background dial (tunnel, census) replaces it.
+    old.status = 'disconnected'
+    let finishOldClose!: () => void
+    old.disconnect.mockImplementationOnce(
+      () =>
+        new Promise<void>((resolve) => {
+          finishOldClose = resolve
+        })
+    )
+
+    const background = manager.connect(target)
+    const rejected = expect(background).rejects.toThrow('cancelled')
+    await manager.disconnect(target.id)
+    finishOldClose()
+    await rejected
+
+    expect(mockState.instances).toHaveLength(1)
+    expect(manager.getConnection(target.id)).toBeUndefined()
+  })
+
   it('leaves a connection whose own reconnect is asking the user alone', async () => {
     const manager = new SshConnectionManager({ onStateChange: vi.fn() })
     const conn = await manager.connect(target)

src/main/ssh/ssh-connection-manager.ts

@@ -63,6 +63,11 @@ export class SshConnectionManager {
       if (existing) {
         this.retainSignIn(target.id, existing)
         await existing.disconnect()
+        // Why: a Disconnect or Remove while the old transport closed cancels this attempt;
+        // registering now would revive the host the user just let go.
+        if (this.connectingTargets.get(target.id) !== attempt) {
+          throw new Error(`Connection to ${target.label} was cancelled`)
+        }
       }
 
       const conn = new SshConnection(target, this.callbacks, this.takeRetainedSignIn(target))