feat: long-running session improvements

- Hang fix: 120s timeout on compression LLM call + raw_stream
  channel-close handling (None => break instead of spinning)
- Supervisor effective active count: stop counting finished
  JoinHandles as occupying capacity slots
- Universal tool result size cap: truncate_if_needed() on
  ToolResult, applied in eval_tool_calls() after escalation block;
  configurable via max_tool_result_chars in AppConfig/AgentConfig
- Windowed compression: compression_keep_last config param keeps
  the N most recent messages visible after compression
- Fix pre-existing flaky test: add #[serial] to
  handle_list_available_unrestricted_when_no_whitelist so it does
  not race with TestConfigDirGuard-based tests that temporarily
  populate the agents data dir

src/config/agent.rs

@@ -531,6 +531,14 @@ impl Agent {
         self.config.compression_threshold
     }
 
+    pub fn max_tool_result_chars(&self) -> Option<usize> {
+        self.config.max_tool_result_chars
+    }
+
+    pub fn compression_keep_last(&self) -> Option<usize> {
+        self.config.compression_keep_last
+    }
+
     pub fn is_dynamic_instructions(&self) -> bool {
         self.config.dynamic_instructions
     }
@@ -679,6 +687,10 @@ pub struct AgentConfig {
     pub memory: Option<bool>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub compression_threshold: Option<usize>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub max_tool_result_chars: Option<usize>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub compression_keep_last: Option<usize>,
     #[serde(default)]
     pub description: String,
     #[serde(default)]

src/config/app_config.rs

@@ -62,8 +62,10 @@ pub struct AppConfig {
 
     pub save_session: Option<bool>,
     pub compression_threshold: usize,
+    pub compression_keep_last: usize,
     pub summarization_prompt: Option<String>,
     pub summary_context_prompt: Option<String>,
+    pub max_tool_result_chars: Option<usize>,
 
     pub memory: Option<bool>,
     pub memory_cap_with_tools: Option<usize>,
@@ -143,8 +145,10 @@ impl Default for AppConfig {
 
             save_session: None,
             compression_threshold: 4000,
+            compression_keep_last: 0,
             summarization_prompt: None,
             summary_context_prompt: None,
+            max_tool_result_chars: None,
 
             memory: None,
             memory_cap_with_tools: None,
@@ -225,8 +229,10 @@ impl AppConfig {
 
             save_session: config.save_session,
             compression_threshold: config.compression_threshold,
+            compression_keep_last: config.compression_keep_last,
             summarization_prompt: config.summarization_prompt,
             summary_context_prompt: config.summary_context_prompt,
+            max_tool_result_chars: config.max_tool_result_chars,
 
             memory: config.memory,
             memory_cap_with_tools: config.memory_cap_with_tools,

src/config/mod.rs

@@ -239,8 +239,10 @@ pub struct Config {
 
     pub save_session: Option<bool>,
     pub compression_threshold: usize,
+    pub compression_keep_last: usize,
     pub summarization_prompt: Option<String>,
     pub summary_context_prompt: Option<String>,
+    pub max_tool_result_chars: Option<usize>,
 
     pub memory: Option<bool>,
     pub memory_cap_with_tools: Option<usize>,
@@ -318,8 +320,10 @@ impl Default for Config {
 
             save_session: None,
             compression_threshold: 4000,
+            compression_keep_last: 0,
             summarization_prompt: None,
             summary_context_prompt: None,
+            max_tool_result_chars: None,
 
             memory: None,
             memory_cap_with_tools: None,

src/config/request_context.rs

@@ -3941,7 +3941,12 @@ impl RequestContext {
             .clone()
             .unwrap_or_else(|| SUMMARIZATION_PROMPT.into());
         let input = Input::from_str(self, &prompt, None)?;
-        let summary = input.fetch_chat_text().await?;
+        let summary = tokio::time::timeout(
+            std::time::Duration::from_secs(120),
+            input.fetch_chat_text(),
+        )
+        .await
+        .map_err(|_| anyhow::anyhow!("Compression LLM call timed out after 120 s"))??;
         let summary_context_prompt = self
             .app
             .config
@@ -3958,8 +3963,13 @@ impl RequestContext {
             String::new()
         };
 
+        let keep_last = self
+            .agent
+            .as_ref()
+            .and_then(|a| a.compression_keep_last())
+            .unwrap_or(self.app.config.compression_keep_last);
         if let Some(session) = self.session.as_mut() {
-            session.compress(format!("{todo_prefix}{summary_context_prompt}{summary}"));
+            session.compress(format!("{todo_prefix}{summary_context_prompt}{summary}"), keep_last);
         }
         self.discontinuous_last_message();
         Ok(())

src/config/session.rs

@@ -570,7 +570,7 @@ impl Session {
         self.compressing = compressing;
     }
 
-    pub fn compress(&mut self, mut prompt: String) {
+    pub fn compress(&mut self, mut prompt: String, keep_last: usize) {
         if let Some(system_prompt) = self.messages.first().and_then(|v| {
             if MessageRole::System == v.role {
                 let content = v.content.to_text();
@@ -582,11 +582,17 @@ impl Session {
         }) {
             prompt = format!("{system_prompt}\n\n{prompt}",);
         }
+        let messages_to_keep = if keep_last > 0 && keep_last < self.messages.len() {
+            self.messages.split_off(self.messages.len() - keep_last)
+        } else {
+            vec![]
+        };
         self.compressed_messages.append(&mut self.messages);
         self.messages.push(Message::new(
             MessageRole::System,
             MessageContent::Text(prompt),
         ));
+        self.messages.extend(messages_to_keep);
         self.dirty = true;
         self.update_tokens();
     }
@@ -1032,7 +1038,7 @@ mod tests {
         assert_eq!(session.messages.len(), 2);
         assert!(session.compressed_messages.is_empty());
 
-        session.compress("Summary of conversation".to_string());
+        session.compress("Summary of conversation".to_string(), 0);
 
         assert!(!session.compressed_messages.is_empty());
         assert_eq!(session.messages.len(), 1);
@@ -1047,7 +1053,7 @@ mod tests {
             MessageContent::Text("hello".to_string()),
         ));
 
-        session.compress("Summary".to_string());
+        session.compress("Summary".to_string(), 0);
 
         assert!(!session.is_empty());
     }

src/function/mod.rs

@@ -184,6 +184,20 @@ pub async fn eval_tool_calls(
         }
     }
 
+    {
+        let max_chars = ctx
+            .agent
+            .as_ref()
+            .and_then(|a| a.max_tool_result_chars())
+            .or_else(|| ctx.app.config.max_tool_result_chars);
+        if let Some(max_chars) = max_chars.filter(|&n| n > 0) {
+            output = output
+                .into_iter()
+                .map(|r| r.truncate_if_needed(max_chars))
+                .collect();
+        }
+    }
+
     Ok(output)
 }
 
@@ -219,6 +233,17 @@ impl ToolResult {
             thinking: vec![],
         }
     }
+
+    pub fn truncate_if_needed(mut self, max_chars: usize) -> Self {
+        let s = self.output.to_string();
+        if s.len() > max_chars {
+            let prefix = s.get(..max_chars).unwrap_or(s.as_str());
+            self.output = json!(format!(
+                "[truncated: tool output exceeded {max_chars} chars]\n{prefix}"
+            ));
+        }
+        self
+    }
 }
 
 #[derive(Debug, Clone, Default)]

src/function/supervisor.rs

@@ -1446,6 +1446,7 @@ mod tests {
     use crate::config::{AppState, WorkingMode};
     use crate::supervisor::escalation::{EscalationQueue, EscalationRequest};
     use serde_json::json;
+    use serial_test::serial;
 
     fn default_app_state() -> Arc<AppState> {
         Arc::new(AppState::test_default())
@@ -1537,6 +1538,7 @@ mod tests {
     }
 
     #[test]
+    #[serial]
     fn handle_list_available_unrestricted_when_no_whitelist() {
         let ctx = ctx_with_supervisor(4, 3);
         let result = handle_list_available(&ctx).unwrap();

src/render/stream.rs

@@ -42,7 +42,9 @@ pub async fn raw_stream(
         if abort_signal.aborted() {
             break;
         }
-        if let Some(evt) = rx.recv().await {
+        match rx.recv().await {
+            None => break,
+            Some(evt) => {
                 if let Some(spinner) = spinner.take() {
                     spinner.stop();
                 }
@@ -58,6 +60,7 @@ pub async fn raw_stream(
                 }
             }
         }
+    }
     if let Some(spinner) = spinner.take() {
         spinner.stop();
     }

src/supervisor/mod.rs

@@ -58,6 +58,13 @@ impl Supervisor {
         self.handles.len()
     }
 
+    pub fn effective_active_count(&self) -> usize {
+        self.handles
+            .values()
+            .filter(|h| !h.join_handle.is_finished())
+            .count()
+    }
+
     pub fn max_concurrent(&self) -> usize {
         self.max_concurrent
     }
@@ -75,10 +82,10 @@ impl Supervisor {
     }
 
     pub fn register(&mut self, handle: AgentHandle) -> Result<()> {
-        if self.handles.len() >= self.max_concurrent {
+        if self.effective_active_count() >= self.max_concurrent {
             bail!(
                 "Cannot spawn agent: at capacity ({}/{})",
-                self.handles.len(),
+                self.effective_active_count(),
                 self.max_concurrent
             );
         }
@@ -188,8 +195,32 @@ mod tests {
 
     #[test]
     fn supervisor_register_rejects_at_capacity() {
+        // Keep the runtime alive in this scope so the spawned task is never
+        // polled (current_thread only polls inside block_on), keeping
+        // join_handle.is_finished() == false and the slot occupied.
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()
+            .unwrap();
+        let join_handle = rt.spawn(async {
+            Ok::<AgentResult, anyhow::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(1, 3);
-        sup.register(make_handle("a1", "explore", 1)).unwrap();
+        sup.register(running_handle).unwrap();
         let result = sup.register(make_handle("a2", "coder", 1));
         assert!(result.is_err());
         assert!(result.unwrap_err().to_string().contains("at capacity"));