feat(TASK-049): classify idle-prompt ctrl-c + ctrl-d as a completed exit

Ctrl-C at the reedline prompt no longer latches the abort signal
unconditionally: latch_prompt_interrupt only marks an interruption when
the supervisor had live agents/jobs to cancel (new
Supervisor::has_active_tasks), so the advertised exit path (ctrl-c at an
idle prompt, then ctrl-d) fires agent.completed at teardown instead of
agent.interrupted. Mid-turn ctrl-c still latches directly via
wait_user_interrupt/poll_abort_signal, preserving the
interrupted-then-exit classification.

Also: probe-lane tests for escalation.answered single-fire,
escalation question env truncation, agent.failed inverse gate, and
hooks probe Scenario I (session.started vs session.resumed); comment
notes on escalation.answered semantics and the agent__cancel blind
spot.

src/supervisor/mod.rs

@@ -190,6 +190,12 @@ impl Supervisor {
             .count()
     }
 
+    /// True when any registered agent or job is still running -- i.e. a
+    /// cancellation right now would actually interrupt in-flight work.
+    pub fn has_active_tasks(&self) -> bool {
+        self.effective_active_count() > 0 || self.active_job_count() > 0
+    }
+
     pub fn max_concurrent(&self) -> usize {
         self.max_concurrent
     }
@@ -449,6 +455,50 @@ mod tests {
         assert!(result.unwrap_err().to_string().contains("at capacity"));
     }
 
+    #[test]
+    fn has_active_tasks_false_when_empty_or_all_finished() {
+        let mut sup = Supervisor::new(4, 3);
+        assert!(!sup.has_active_tasks());
+        // make_handle drops its runtime, aborting the task, so the
+        // registered agent is already finished.
+        sup.register(make_handle("a1", "explore", 1)).unwrap();
+        assert!(!sup.has_active_tasks());
+    }
+
+    #[test]
+    fn has_active_tasks_true_with_running_agent() {
+        // Keep the runtime alive so the task is never polled and the agent
+        // counts as running.
+        let rt = Builder::new_current_thread().enable_all().build().unwrap();
+        let join_handle = rt.spawn(async {
+            Ok::<AgentResult, Error>(AgentResult {
+                id: "done".into(),
+                agent_name: "test".into(),
+                output: "result".into(),
+                exit_status: AgentExitStatus::Completed,
+            })
+        });
+        let running_handle = AgentHandle {
+            id: "a1".to_string(),
+            agent_name: "explore".to_string(),
+            depth: 1,
+            inbox: Arc::new(Inbox::new()),
+            abort_signal: create_abort_signal(),
+            join_handle,
+            child_supervisor: None,
+        };
+        let mut sup = Supervisor::new(4, 3);
+        sup.register(running_handle).unwrap();
+        assert!(sup.has_active_tasks());
+    }
+
+    #[test]
+    fn has_active_tasks_true_with_running_job() {
+        let mut sup = Supervisor::new(4, 3).with_max_concurrent_jobs(1);
+        sup.register(make_job("j1", create_abort_signal())).unwrap();
+        assert!(sup.has_active_tasks());
+    }
+
     #[test]
     fn supervisor_register_rejects_exceeding_depth() {
         let mut sup = Supervisor::new(4, 2);