fix: bound safe-boundary pause escalation

crates/agen/src/engine.rs

@@ -1284,6 +1284,7 @@ impl<C: LlmClient, S: EngineState, A> Engine<C, S, A> {
         // commit-before-publish boundary.
         let mut terminal_call_ids = HashSet::new();
         let mut pause_requested = false;
+        let mut pause_deadline = None;
         for result in synthetic_results {
             self.finalize_and_commit_tool_result(
                 history,
@@ -1319,12 +1320,20 @@ impl<C: LlmClient, S: EngineState, A> Engine<C, S, A> {
                 }
                 pause = self.pause_rx.recv(), if !pause_requested => {
                     if pause.is_some() {
-                        // Pause is a safe-boundary request: do not cancel provider
-                        // operations that already started. Drain all confirmed
-                        // terminal results, then yield control to Worker.
+                        // Pause first waits for already-started tools to reach a
+                        // natural safe boundary. If they do not, Worker policy
+                        // escalates to the same explicit cancel-and-confirm path.
                         pause_requested = true;
+                        pause_deadline = Some(
+                            TokioInstant::now()
+                                + self.tool_execution_policy.pause_safe_boundary_timeout,
+                        );
                     }
                 }
+                _ = tokio::time::sleep_until(pause_deadline.unwrap_or_else(TokioInstant::now)), if pause_deadline.is_some() => {
+                    pause_deadline = None;
+                    let _ = self.cancel_tx.try_send(());
+                }
                 cancel = self.cancel_rx.recv() => {
                     if cancel.is_some() {
                         info!("Tool execution cancellation requested");
@@ -1404,6 +1413,9 @@ impl<C: LlmClient, S: EngineState, A> Engine<C, S, A> {
                     }
 
                     self.timeline.abort_current_block();
+                    if pause_requested {
+                        return Ok(ToolExecutionResult::Paused);
+                    }
                     return Err(EngineError::Cancelled);
                 }
             }

crates/agen/src/tool.rs

@@ -490,6 +490,9 @@ impl ToolExecutionHandle {
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct ToolExecutionPolicy {
+    /// Time a pause waits for already-started providers to reach a natural safe
+    /// boundary before escalating to explicit cooperative cancellation.
+    pub pause_safe_boundary_timeout: std::time::Duration,
     /// Maximum time allowed for a provider to accept one cooperative
     /// cancellation request.
     pub cancellation_request_timeout: std::time::Duration,
@@ -501,6 +504,7 @@ pub struct ToolExecutionPolicy {
 impl Default for ToolExecutionPolicy {
     fn default() -> Self {
         Self {
+            pause_safe_boundary_timeout: std::time::Duration::from_millis(100),
             cancellation_request_timeout: std::time::Duration::from_millis(100),
             terminal_confirmation_timeout: std::time::Duration::from_millis(500),
         }

crates/agen/tests/parallel_execution_test.rs

@@ -12,7 +12,7 @@ use agen::tool::{
     Tool, ToolDefinition, ToolError, ToolExecutionContext, ToolMeta, ToolOutput, ToolResult,
     ToolResultDisposition,
 };
-use agen::{Engine, History, Item};
+use agen::{Engine, History, Item, ToolExecutionPolicy};
 use async_trait::async_trait;
 
 mod common;
@@ -610,7 +610,7 @@ async fn pause_waits_for_started_tool_terminal_without_cancelling_provider() {
         .await
         .expect("tool execution starts");
         pause.send(()).await.unwrap();
-        tokio::time::sleep(Duration::from_millis(100)).await;
+        tokio::time::sleep(Duration::from_millis(50)).await;
         release.notify_one();
     });
 
@@ -619,7 +619,7 @@ async fn pause_waits_for_started_tool_terminal_without_cancelling_provider() {
     let output = engine.run(&mut history, "pause safely").await;
     control.await.unwrap();
 
-    assert!(started_at.elapsed() >= Duration::from_millis(100));
+    assert!(started_at.elapsed() >= Duration::from_millis(50));
     assert_eq!(tool.calls.load(Ordering::SeqCst), 1);
     assert_eq!(tool.cancellations.load(Ordering::SeqCst), 0);
     assert!(matches!(output.result, agen::EngineRunExit::Paused));
@@ -633,6 +633,53 @@ async fn pause_waits_for_started_tool_terminal_without_cancelling_provider() {
     )));
 }
 
+#[tokio::test]
+async fn pause_escalates_to_explicit_cancel_and_confirm_after_safe_boundary_deadline() {
+    let client = MockLlmClient::with_responses(vec![vec![
+        Event::tool_use_start(0, "call_pause_cancel", "cooperative"),
+        Event::tool_input_delta(0, r#"{}"#),
+        Event::tool_use_stop(0),
+        Event::Status(StatusEvent {
+            status: ResponseStatus::Completed,
+        }),
+    ]]);
+    let mut engine = Engine::new(client);
+    engine.set_tool_execution_policy(ToolExecutionPolicy {
+        pause_safe_boundary_timeout: Duration::from_millis(20),
+        cancellation_request_timeout: Duration::from_millis(50),
+        terminal_confirmation_timeout: Duration::from_millis(100),
+    });
+    let tool = CooperativeCancelTool::new();
+    engine.register_tool(tool.definition());
+
+    let pause = engine.pause_sender();
+    let calls = Arc::clone(&tool.calls);
+    let control = tokio::spawn(async move {
+        tokio::time::timeout(Duration::from_secs(1), async {
+            while calls.load(Ordering::SeqCst) == 0 {
+                tokio::task::yield_now().await;
+            }
+        })
+        .await
+        .expect("tool execution starts");
+        pause.send(()).await.unwrap();
+    });
+
+    let mut history = History::new();
+    let output = engine.run(&mut history, "pause with escalation").await;
+    control.await.unwrap();
+
+    assert!(matches!(output.result, agen::EngineRunExit::Paused));
+    assert!(history.iter().any(|entry| matches!(
+        &entry.item,
+        Item::ToolResult {
+            call_id,
+            disposition: ToolResultDisposition::Cancelled,
+            ..
+        } if call_id == "call_pause_cancel"
+    )));
+}
+
 #[tokio::test]
 async fn cancellation_completion_race_commits_one_terminal_output() {
     for iteration in 0..24u64 {