acp: Remember following state (#36793)

A beta user reported that following was "lost" when asking for
confirmation, I
suspect they moved their cursor in the agent file while reviewing the
change.
Now we will resume following when the agent starts up again.

Release Notes:

- N/A

crates/acp_thread/src/acp_thread.rs

@@ -774,7 +774,7 @@ pub enum AcpThreadEvent {
 
 impl EventEmitter<AcpThreadEvent> for AcpThread {}
 
-#[derive(PartialEq, Eq)]
+#[derive(PartialEq, Eq, Debug)]
 pub enum ThreadStatus {
     Idle,
     WaitingForToolConfirmation,