fix(channel): merge delivery instructions into initial system message

Some models (e.g. Qwen 3.5) enforce that all system messages must appear
at the beginning of the conversation. The Telegram delivery instructions
were appended as a separate system message after the user message,
causing a Jinja template error. Merge them into the first system message
instead.

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

src/channels/mod.rs

@@ -626,14 +626,14 @@ async fn process_channel_message(ctx: Arc<ChannelRuntimeContext>, msg: traits::C
         .cloned()
         .unwrap_or_default();
 
-    let mut history = vec![ChatMessage::system(ctx.system_prompt.as_str())];
+    let system_prompt = match channel_delivery_instructions(&msg.channel) {
+        Some(instructions) => format!("{}\n\n{instructions}", ctx.system_prompt),
+        None => ctx.system_prompt.to_string(),
+    };
+    let mut history = vec![ChatMessage::system(&system_prompt)];
     history.append(&mut prior_turns);
     history.push(ChatMessage::user(&enriched_message));
 
-    if let Some(instructions) = channel_delivery_instructions(&msg.channel) {
-        history.push(ChatMessage::system(instructions));
-    }
-
     // Determine if this channel supports streaming draft updates
     let use_streaming = target_channel
         .as_ref()
@@ -2304,6 +2304,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2356,6 +2357,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2417,6 +2419,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2499,6 +2502,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2557,6 +2561,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2610,6 +2615,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -2714,6 +2720,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         let (tx, rx) = tokio::sync::mpsc::channel::<traits::ChannelMessage>(4);
@@ -2784,6 +2791,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(
@@ -3174,6 +3182,7 @@ mod tests {
             reliability: Arc::new(crate::config::ReliabilityConfig::default()),
             provider_runtime_options: providers::ProviderRuntimeOptions::default(),
             workspace_dir: Arc::new(std::env::temp_dir()),
+            channel_message_timeout_secs: 300,
         });
 
         process_channel_message(