feat(agent): queue and merge messages during active turns

src/agent/agent_loop.rs

@@ -1153,8 +1153,92 @@ impl Agent {
         // Process based on submission type
         let result = match submission {
             Submission::UserInput { content } => {
-                self.process_user_input(message, session, thread_id, &content)
-                    .await
+                let mut result = self
+                    .process_user_input(message, session.clone(), thread_id, &content)
+                    .await;
+
+                // Drain any messages queued during processing.
+                // Messages are merged (newline-separated) so the LLM receives
+                // full context from rapid consecutive inputs instead of
+                // processing each as a separate turn with partial context (#259).
+                //
+                // Only `Response` continues the drain — the user got a normal
+                // reply and there may be more queued messages to process.
+                //
+                // Everything else stops the loop:
+                // - `NeedApproval`: thread is blocked on user approval
+                // - `Interrupted`: turn was cancelled
+                // - `Ok`: control-command acknowledgment (including the "queued"
+                //    ack returned when a message arrives during Processing)
+                // - `Error`: soft error — draining more messages after an error
+                //    would produce confusing interleaved output
+                // - `Err(_)`: hard error
+                while let Ok(SubmissionResult::Response { content: outgoing }) = &result {
+                    let merged = {
+                        let mut sess = session.lock().await;
+                        sess.threads
+                            .get_mut(&thread_id)
+                            .and_then(|t| t.drain_pending_messages())
+                    };
+                    let Some(next_content) = merged else {
+                        break;
+                    };
+
+                    tracing::debug!(
+                        thread_id = %thread_id,
+                        merged_len = next_content.len(),
+                        "Drain loop: processing merged queued messages"
+                    );
+
+                    // Send the completed turn's response before starting the next.
+                    //
+                    // Known limitations:
+                    // - One-shot channels (HttpChannel) consume the response
+                    //   sender on the first respond() call keyed by msg.id.
+                    //   Subsequent calls (including the outer handler's final
+                    //   respond) are silently dropped. For one-shot channels
+                    //   only this intermediate response is delivered.
+                    // - All drain-loop responses are routed via the original
+                    //   `message`, so channels that key routing on message
+                    //   identity will attribute every response to the first
+                    //   message. This is acceptable for the current
+                    //   single-user-per-thread model.
+                    if let Err(e) = self
+                        .channels
+                        .respond(message, OutgoingResponse::text(outgoing.clone()))
+                        .await
+                    {
+                        tracing::warn!(
+                            thread_id = %thread_id,
+                            "Failed to send intermediate drain-loop response: {e}"
+                        );
+                    }
+
+                    // Process merged queued messages as a single turn.
+                    // Use a message clone with cleared attachments so
+                    // augment_with_attachments doesn't re-apply the original
+                    // message's attachments to unrelated queued text.
+                    let mut queued_msg = message.clone();
+                    queued_msg.attachments.clear();
+                    result = self
+                        .process_user_input(&queued_msg, session.clone(), thread_id, &next_content)
+                        .await;
+
+                    // If processing failed, re-queue the drained content so it
+                    // isn't lost. It will be picked up on the next successful turn.
+                    if !matches!(&result, Ok(SubmissionResult::Response { .. })) {
+                        let mut sess = session.lock().await;
+                        if let Some(thread) = sess.threads.get_mut(&thread_id) {
+                            thread.requeue_drained(next_content);
+                            tracing::debug!(
+                                thread_id = %thread_id,
+                                "Re-queued drained content after non-Response result"
+                            );
+                        }
+                    }
+                }
+
+                result
             }
             Submission::SystemCommand { command, args } => {
                 tracing::debug!(

src/agent/session.rs

@@ -10,7 +10,7 @@
 //! - Compaction: Summarize old turns to save context
 //! - Resume: Continue from a saved checkpoint
 
-use std::collections::{HashMap, HashSet};
+use std::collections::{HashMap, HashSet, VecDeque};
 
 use chrono::{DateTime, TimeDelta, Utc};
 use serde::{Deserialize, Serialize};
@@ -222,8 +222,17 @@ pub struct Thread {
     /// Pending auth token request (thread is in auth mode).
     #[serde(default)]
     pub pending_auth: Option<PendingAuth>,
+    /// Messages queued while the thread was processing a turn.
+    #[serde(default, skip_serializing_if = "VecDeque::is_empty")]
+    pub pending_messages: VecDeque<String>,
 }
 
+/// Maximum number of messages that can be queued while a thread is processing.
+/// 10 merged messages can produce a large combined input for the LLM, but this
+/// is acceptable for the personal assistant use case where a single user sends
+/// rapid follow-ups. The drain loop processes them as one newline-delimited turn.
+pub const MAX_PENDING_MESSAGES: usize = 10;
+
 impl Thread {
     /// Create a new thread.
     pub fn new(session_id: Uuid) -> Self {
@@ -238,6 +247,7 @@ impl Thread {
             metadata: serde_json::Value::Null,
             pending_approval: None,
             pending_auth: None,
+            pending_messages: VecDeque::new(),
         }
     }
 
@@ -254,6 +264,7 @@ impl Thread {
             metadata: serde_json::Value::Null,
             pending_approval: None,
             pending_auth: None,
+            pending_messages: VecDeque::new(),
         }
     }
 
@@ -272,6 +283,47 @@ impl Thread {
         self.turns.last_mut()
     }
 
+    /// Queue a message for processing after the current turn completes.
+    /// Returns `false` if the queue is at capacity ([`MAX_PENDING_MESSAGES`]).
+    pub fn queue_message(&mut self, content: String) -> bool {
+        if self.pending_messages.len() >= MAX_PENDING_MESSAGES {
+            return false;
+        }
+        self.pending_messages.push_back(content);
+        self.updated_at = Utc::now();
+        true
+    }
+
+    /// Take the next pending message from the queue.
+    pub fn take_pending_message(&mut self) -> Option<String> {
+        self.pending_messages.pop_front()
+    }
+
+    /// Drain all pending messages from the queue.
+    /// Multiple messages are joined with newlines so the LLM receives
+    /// full context from rapid consecutive inputs (#259).
+    pub fn drain_pending_messages(&mut self) -> Option<String> {
+        if self.pending_messages.is_empty() {
+            return None;
+        }
+        let parts: Vec<String> = self.pending_messages.drain(..).collect();
+        self.updated_at = Utc::now();
+        Some(parts.join("\n"))
+    }
+
+    /// Re-queue previously drained content at the front of the queue.
+    /// Used to preserve user input when the drain loop fails to process
+    /// merged messages (soft error, hard error, interrupt).
+    ///
+    /// This intentionally bypasses [`MAX_PENDING_MESSAGES`] — the content
+    /// was already counted against the cap before draining. The overshoot
+    /// is bounded to 1 entry (the re-queued merged string) plus any new
+    /// messages that arrived during the failed attempt.
+    pub fn requeue_drained(&mut self, content: String) {
+        self.pending_messages.push_front(content);
+        self.updated_at = Utc::now();
+    }
+
     /// Start a new turn with user input.
     pub fn start_turn(&mut self, user_input: impl Into<String>) -> &mut Turn {
         let turn_number = self.turns.len();
@@ -335,11 +387,12 @@ impl Thread {
         self.pending_auth.take()
     }
 
-    /// Interrupt the current turn.
+    /// Interrupt the current turn and discard any queued messages.
     pub fn interrupt(&mut self) {
         if let Some(turn) = self.turns.last_mut() {
             turn.interrupt();
         }
+        self.pending_messages.clear();
         self.state = ThreadState::Interrupted;
         self.updated_at = Utc::now();
     }
@@ -1392,4 +1445,165 @@ mod tests {
         );
         assert!(tool_result_content.ends_with("..."));
     }
+
+    #[test]
+    fn test_thread_message_queue() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Queue is initially empty
+        assert!(thread.pending_messages.is_empty());
+        assert!(thread.take_pending_message().is_none());
+
+        // Queue messages and verify FIFO ordering
+        assert!(thread.queue_message("first".to_string()));
+        assert!(thread.queue_message("second".to_string()));
+        assert!(thread.queue_message("third".to_string()));
+        assert_eq!(thread.pending_messages.len(), 3);
+
+        assert_eq!(thread.take_pending_message(), Some("first".to_string()));
+        assert_eq!(thread.take_pending_message(), Some("second".to_string()));
+        assert_eq!(thread.take_pending_message(), Some("third".to_string()));
+        assert!(thread.take_pending_message().is_none());
+
+        // Fill to capacity — all 10 should succeed
+        for i in 0..MAX_PENDING_MESSAGES {
+            assert!(thread.queue_message(format!("msg-{}", i)));
+        }
+        assert_eq!(thread.pending_messages.len(), MAX_PENDING_MESSAGES);
+
+        // 11th message rejected by queue_message itself
+        assert!(!thread.queue_message("overflow".to_string()));
+        assert_eq!(thread.pending_messages.len(), MAX_PENDING_MESSAGES);
+
+        // Drain and verify order
+        for i in 0..MAX_PENDING_MESSAGES {
+            assert_eq!(thread.take_pending_message(), Some(format!("msg-{}", i)));
+        }
+        assert!(thread.take_pending_message().is_none());
+    }
+
+    #[test]
+    fn test_thread_message_queue_serialization() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Empty queue should not appear in serialization (skip_serializing_if)
+        let json = serde_json::to_string(&thread).unwrap();
+        assert!(!json.contains("pending_messages"));
+
+        // Non-empty queue should serialize and deserialize
+        thread.queue_message("queued msg".to_string());
+        let json = serde_json::to_string(&thread).unwrap();
+        assert!(json.contains("pending_messages"));
+        assert!(json.contains("queued msg"));
+
+        let restored: Thread = serde_json::from_str(&json).unwrap();
+        assert_eq!(restored.pending_messages.len(), 1);
+        assert_eq!(restored.pending_messages[0], "queued msg");
+    }
+
+    #[test]
+    fn test_thread_message_queue_default_on_old_data() {
+        // Deserialization of old data without pending_messages should default to empty
+        let thread = Thread::new(Uuid::new_v4());
+        let json = serde_json::to_string(&thread).unwrap();
+
+        // The field is absent (skip_serializing_if), simulating old data
+        assert!(!json.contains("pending_messages"));
+        let restored: Thread = serde_json::from_str(&json).unwrap();
+        assert!(restored.pending_messages.is_empty());
+    }
+
+    #[test]
+    fn test_interrupt_clears_pending_messages() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Start a turn so there's something to interrupt
+        thread.start_turn("initial input");
+
+        // Queue several messages while "processing"
+        thread.queue_message("queued-1".to_string());
+        thread.queue_message("queued-2".to_string());
+        thread.queue_message("queued-3".to_string());
+        assert_eq!(thread.pending_messages.len(), 3);
+
+        // Interrupt should clear the queue
+        thread.interrupt();
+        assert!(thread.pending_messages.is_empty());
+        assert_eq!(thread.state, ThreadState::Interrupted);
+    }
+
+    #[test]
+    fn test_thread_state_idle_after_full_drain() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Simulate a full drain cycle: start turn, queue messages, complete turn,
+        // then drain all queued messages as a single merged turn (#259).
+        thread.start_turn("turn 1");
+        assert_eq!(thread.state, ThreadState::Processing);
+
+        thread.queue_message("queued-a".to_string());
+        thread.queue_message("queued-b".to_string());
+
+        // Complete the turn (simulates process_user_input finishing)
+        thread.complete_turn("response 1");
+        assert_eq!(thread.state, ThreadState::Idle);
+
+        // Drain: merge all queued messages and process as a single turn
+        let merged = thread.drain_pending_messages().unwrap();
+        assert_eq!(merged, "queued-a\nqueued-b");
+        thread.start_turn(&merged);
+        thread.complete_turn("response for merged");
+
+        // Queue is fully drained, thread is idle
+        assert!(thread.drain_pending_messages().is_none());
+        assert!(thread.pending_messages.is_empty());
+        assert_eq!(thread.state, ThreadState::Idle);
+    }
+
+    #[test]
+    fn test_drain_pending_messages_merges_with_newlines() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Empty queue returns None
+        assert!(thread.drain_pending_messages().is_none());
+
+        // Single message returned as-is (no trailing newline)
+        thread.queue_message("only one".to_string());
+        assert_eq!(
+            thread.drain_pending_messages(),
+            Some("only one".to_string()),
+        );
+        assert!(thread.pending_messages.is_empty());
+
+        // Multiple messages joined with newlines
+        thread.queue_message("hey".to_string());
+        thread.queue_message("can you check the server".to_string());
+        thread.queue_message("it started 10 min ago".to_string());
+        assert_eq!(
+            thread.drain_pending_messages(),
+            Some("hey\ncan you check the server\nit started 10 min ago".to_string()),
+        );
+        assert!(thread.pending_messages.is_empty());
+
+        // Queue is empty after drain
+        assert!(thread.drain_pending_messages().is_none());
+    }
+
+    #[test]
+    fn test_requeue_drained_preserves_content_at_front() {
+        let mut thread = Thread::new(Uuid::new_v4());
+
+        // Re-queue into empty queue
+        thread.requeue_drained("failed batch".to_string());
+        assert_eq!(thread.pending_messages.len(), 1);
+        assert_eq!(thread.pending_messages[0], "failed batch");
+
+        // New messages go behind the re-queued content
+        thread.queue_message("new msg".to_string());
+        assert_eq!(thread.pending_messages.len(), 2);
+
+        // Drain should return re-queued content first (front of queue)
+        let merged = thread.drain_pending_messages().unwrap();
+        assert_eq!(merged, "failed batch\nnew msg");
+    }
 }