feat(channels): add threading support to message channels

Add optional thread_ts field to ChannelMessage and SendMessage for
platform-specific threading (e.g. Slack threads, Discord threads).

- ChannelMessage.thread_ts captures incoming thread context
- SendMessage.thread_ts propagates thread context to replies
- SendMessage::in_thread() builder for fluent API
- Slack: send with thread_ts, capture ts from incoming messages
- All reply paths in runtime preserve thread context via in_thread()
- All other channels initialize thread_ts: None (forward-compatible)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/channels/cli.rs

@@ -47,6 +47,7 @@ impl Channel for CliChannel {
                     .duration_since(std::time::UNIX_EPOCH)
                     .unwrap_or_default()
                     .as_secs(),
+                thread_ts: None,
             };
 
             if tx.send(msg).await.is_err() {
@@ -107,6 +108,7 @@ mod tests {
             content: "hello".into(),
             channel: "cli".into(),
             timestamp: 1_234_567_890,
+            thread_ts: None,
         };
         assert_eq!(msg.id, "test-id");
         assert_eq!(msg.sender, "user");
@@ -125,6 +127,7 @@ mod tests {
             content: "c".into(),
             channel: "ch".into(),
             timestamp: 0,
+            thread_ts: None,
         };
         let cloned = msg.clone();
         assert_eq!(cloned.id, msg.id);

src/channels/dingtalk.rs

@@ -274,6 +274,7 @@ impl Channel for DingTalkChannel {
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()
                             .as_secs(),
+                        thread_ts: None,
                     };
 
                     if tx.send(channel_msg).await.is_err() {

src/channels/discord.rs

@@ -413,6 +413,7 @@ impl Channel for DiscordChannel {
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()
                             .as_secs(),
+                        thread_ts: None,
                     };
 
                     if tx.send(channel_msg).await.is_err() {

src/channels/email_channel.rs

@@ -443,6 +443,7 @@ impl EmailChannel {
                 content: email.content,
                 channel: "email".to_string(),
                 timestamp: email.timestamp,
+                thread_ts: None,
             };
 
             if tx.send(msg).await.is_err() {

src/channels/imessage.rs

@@ -231,6 +231,7 @@ end tell"#
                                 .duration_since(std::time::UNIX_EPOCH)
                                 .unwrap_or_default()
                                 .as_secs(),
+                            thread_ts: None,
                         };
 
                         if tx.send(msg).await.is_err() {

src/channels/irc.rs

@@ -574,6 +574,7 @@ impl Channel for IrcChannel {
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()
                             .as_secs(),
+                        thread_ts: None,
                     };
 
                     if tx.send(channel_msg).await.is_err() {

src/channels/lark.rs

@@ -474,6 +474,7 @@ impl LarkChannel {
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()
                             .as_secs(),
+                        thread_ts: None,
                     };
 
                     tracing::debug!("Lark WS: message in {}", lark_msg.chat_id);
@@ -635,6 +636,7 @@ impl LarkChannel {
             content: text,
             channel: "lark".to_string(),
             timestamp,
+            thread_ts: None,
         });
 
         messages

src/channels/linq.rs

@@ -178,6 +178,7 @@ impl LinqChannel {
             content,
             channel: "linq".to_string(),
             timestamp,
+            thread_ts: None,
         });
 
         messages

src/channels/matrix.rs

@@ -596,6 +596,7 @@ impl Channel for MatrixChannel {
                         .duration_since(std::time::UNIX_EPOCH)
                         .unwrap_or_default()
                         .as_secs(),
+                    thread_ts: None,
                 };
 
                 let _ = tx.send(msg).await;

src/channels/mattermost.rs

@@ -321,6 +321,7 @@ impl MattermostChannel {
             channel: "mattermost".to_string(),
             #[allow(clippy::cast_sign_loss)]
             timestamp: (create_at / 1000) as u64,
+            thread_ts: None,
         })
     }
 }

src/channels/mod.rs

@@ -442,7 +442,7 @@ async fn handle_runtime_command_if_needed(
     };
 
     if let Err(err) = channel
-        .send(&SendMessage::new(response, &msg.reply_target))
+        .send(&SendMessage::new(response, &msg.reply_target).in_thread(msg.thread_ts.clone()))
         .await
     {
         tracing::warn!(
@@ -592,7 +592,7 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
             );
             if let Some(channel) = target_channel.as_ref() {
                 let _ = channel
-                    .send(&SendMessage::new(message, &msg.reply_target))
+                    .send(&SendMessage::new(message, &msg.reply_target).in_thread(msg.thread_ts.clone()))
                     .await;
             }
             return;
@@ -658,7 +658,7 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
     let draft_message_id = if use_streaming {
         if let Some(channel) = target_channel.as_ref() {
             match channel
-                .send_draft(&SendMessage::new("...", &msg.reply_target))
+                .send_draft(&SendMessage::new("...", &msg.reply_target).in_thread(msg.thread_ts.clone()))
                 .await
             {
                 Ok(id) => id,
@@ -769,11 +769,11 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
                     {
                         tracing::warn!("Failed to finalize draft: {e}; sending as new message");
                         let _ = channel
-                            .send(&SendMessage::new(&response, &msg.reply_target))
+                            .send(&SendMessage::new(&response, &msg.reply_target).in_thread(msg.thread_ts.clone()))
                             .await;
                     }
                 } else if let Err(e) = channel
-                    .send(&SendMessage::new(response, &msg.reply_target))
+                    .send(&SendMessage::new(response, &msg.reply_target).in_thread(msg.thread_ts.clone()))
                     .await
                 {
                     eprintln!("  ❌ Failed to reply on {}: {e}", channel.name());
@@ -795,7 +795,7 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
                         .send(&SendMessage::new(
                             format!("⚠️ Error: {e}"),
                             &msg.reply_target,
-                        ))
+                        ).in_thread(msg.thread_ts.clone()))
                         .await;
                 }
             }
@@ -816,7 +816,7 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
                         .await;
                 } else {
                     let _ = channel
-                        .send(&SendMessage::new(error_text, &msg.reply_target))
+                        .send(&SendMessage::new(error_text, &msg.reply_target).in_thread(msg.thread_ts.clone()))
                         .await;
                 }
             }
@@ -2350,6 +2350,7 @@ mod tests {
                 content: "What is the BTC price now?".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 1,
+                thread_ts: None,
             },
         )
         .await;
@@ -2403,6 +2404,7 @@ mod tests {
                 content: "What is the BTC price now?".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 2,
+                thread_ts: None,
             },
         )
         .await;
@@ -2465,6 +2467,7 @@ mod tests {
                 content: "/models openrouter".to_string(),
                 channel: "telegram".to_string(),
                 timestamp: 1,
+                thread_ts: None,
             },
         )
         .await;
@@ -2548,6 +2551,7 @@ mod tests {
                 content: "hello routed provider".to_string(),
                 channel: "telegram".to_string(),
                 timestamp: 2,
+                thread_ts: None,
             },
         )
         .await;
@@ -2607,6 +2611,7 @@ mod tests {
                 content: "Loop until done".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 1,
+                thread_ts: None,
             },
         )
         .await;
@@ -2661,6 +2666,7 @@ mod tests {
                 content: "Loop forever".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 2,
+                thread_ts: None,
             },
         )
         .await;
@@ -2765,6 +2771,7 @@ mod tests {
             content: "hello".to_string(),
             channel: "test-channel".to_string(),
             timestamp: 1,
+            thread_ts: None,
         })
         .await
         .unwrap();
@@ -2775,6 +2782,7 @@ mod tests {
             content: "world".to_string(),
             channel: "test-channel".to_string(),
             timestamp: 2,
+            thread_ts: None,
         })
         .await
         .unwrap();
@@ -2837,6 +2845,7 @@ mod tests {
                 content: "hello".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 1,
+                thread_ts: None,
             },
         )
         .await;
@@ -3097,6 +3106,7 @@ mod tests {
             content: "hello".into(),
             channel: "slack".into(),
             timestamp: 1,
+            thread_ts: None,
         };
 
         assert_eq!(conversation_memory_key(&msg), "slack_U123_msg_abc123");
@@ -3111,6 +3121,7 @@ mod tests {
             content: "first".into(),
             channel: "slack".into(),
             timestamp: 1,
+            thread_ts: None,
         };
         let msg2 = traits::ChannelMessage {
             id: "msg_2".into(),
@@ -3119,6 +3130,7 @@ mod tests {
             content: "second".into(),
             channel: "slack".into(),
             timestamp: 2,
+            thread_ts: None,
         };
 
         assert_ne!(
@@ -3139,6 +3151,7 @@ mod tests {
             content: "I'm Paul".into(),
             channel: "slack".into(),
             timestamp: 1,
+            thread_ts: None,
         };
         let msg2 = traits::ChannelMessage {
             id: "msg_2".into(),
@@ -3147,6 +3160,7 @@ mod tests {
             content: "I'm 45".into(),
             channel: "slack".into(),
             timestamp: 2,
+            thread_ts: None,
         };
 
         mem.store(
@@ -3228,6 +3242,7 @@ mod tests {
                 content: "hello".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 1,
+                thread_ts: None,
             },
         )
         .await;
@@ -3241,6 +3256,7 @@ mod tests {
                 content: "follow up".to_string(),
                 channel: "test-channel".to_string(),
                 timestamp: 2,
+                thread_ts: None,
             },
         )
         .await;

src/channels/qq.rs

@@ -377,6 +377,7 @@ impl Channel for QQChannel {
                                     .duration_since(std::time::UNIX_EPOCH)
                                     .unwrap_or_default()
                                     .as_secs(),
+                                thread_ts: None,
                             };
 
                             if tx.send(channel_msg).await.is_err() {
@@ -415,6 +416,7 @@ impl Channel for QQChannel {
                                     .duration_since(std::time::UNIX_EPOCH)
                                     .unwrap_or_default()
                                     .as_secs(),
+                                thread_ts: None,
                             };
 
                             if tx.send(channel_msg).await.is_err() {

src/channels/signal.rs

@@ -265,6 +265,7 @@ impl SignalChannel {
             content: text.to_string(),
             channel: "signal".to_string(),
             timestamp: timestamp / 1000, // millis → secs
+            thread_ts: None,
         })
     }
 }

src/channels/slack.rs

@@ -54,11 +54,15 @@ impl Channel for SlackChannel {
     }
 
     async fn send(&self, message: &SendMessage) -> anyhow::Result<()> {
-        let body = serde_json::json!({
+        let mut body = serde_json::json!({
             "channel": message.recipient,
             "text": message.content
         });
 
+        if let Some(ref ts) = message.thread_ts {
+            body["thread_ts"] = serde_json::json!(ts);
+        }
+
         let resp = self
             .http_client()
             .post("https://slack.com/api/chat.postMessage")
@@ -170,6 +174,7 @@ impl Channel for SlackChannel {
                             .duration_since(std::time::UNIX_EPOCH)
                             .unwrap_or_default()
                             .as_secs(),
+                        thread_ts: Some(ts.to_string()),
                     };
 
                     if tx.send(channel_msg).await.is_err() {

src/channels/telegram.rs

@@ -819,6 +819,7 @@ Allowlist Telegram username (without '@') or numeric user ID.",
                 .duration_since(std::time::UNIX_EPOCH)
                 .unwrap_or_default()
                 .as_secs(),
+            thread_ts: None,
         })
     }
 

src/channels/traits.rs

@@ -9,6 +9,9 @@ pub struct ChannelMessage {
     pub content: String,
     pub channel: String,
     pub timestamp: u64,
+    /// Platform thread identifier (e.g. Slack `ts`, Discord thread ID).
+    /// When set, replies should be posted as threaded responses.
+    pub thread_ts: Option<String>,
 }
 
 /// Message to send through a channel
@@ -17,6 +20,8 @@ pub struct SendMessage {
     pub content: String,
     pub recipient: String,
     pub subject: Option<String>,
+    /// Platform thread identifier for threaded replies (e.g. Slack `thread_ts`).
+    pub thread_ts: Option<String>,
 }
 
 impl SendMessage {
@@ -26,6 +31,7 @@ impl SendMessage {
             content: content.into(),
             recipient: recipient.into(),
             subject: None,
+            thread_ts: None,
         }
     }
 
@@ -39,8 +45,15 @@ impl SendMessage {
             content: content.into(),
             recipient: recipient.into(),
             subject: Some(subject.into()),
+            thread_ts: None,
         }
     }
+
+    /// Set the thread identifier for threaded replies.
+    pub fn in_thread(mut self, thread_ts: Option<String>) -> Self {
+        self.thread_ts = thread_ts;
+        self
+    }
 }
 
 /// Core channel trait — implement for any messaging platform
@@ -129,6 +142,7 @@ mod tests {
                 content: "hello".into(),
                 channel: "dummy".into(),
                 timestamp: 123,
+                thread_ts: None,
             })
             .await
             .map_err(|e| anyhow::anyhow!(e.to_string()))
@@ -144,6 +158,7 @@ mod tests {
             content: "ping".into(),
             channel: "dummy".into(),
             timestamp: 999,
+            thread_ts: None,
         };
 
         let cloned = message.clone();

src/channels/whatsapp.rs

@@ -140,6 +140,7 @@ impl WhatsAppChannel {
                         content,
                         channel: "whatsapp".to_string(),
                         timestamp,
+                        thread_ts: None,
                     });
                 }
             }

src/gateway/mod.rs

@@ -1450,6 +1450,7 @@ mod tests {
             content: "hello".into(),
             channel: "whatsapp".into(),
             timestamp: 1,
+            thread_ts: None,
         };
 
         let key = whatsapp_memory_key(&msg);