feat: group chat privacy, channel-aware prompts, and safety hardening (#285)

Prevent personal memory (MEMORY.md) from leaking into group chat contexts
by adding system_prompt_for_context(is_group_chat) to the workspace. Add
channel-specific formatting hints (Discord, Telegram, Slack, WhatsApp),
runtime metadata injection, group chat behavioral guidance with NO_REPLY
silent token, safety rules in the system prompt, tool call style guidance,
wrap_external_content() for untrusted data, and improved workspace seed
files with richer identity/soul/agent templates and heartbeat checklist.

Co-authored-by: Claude Opus 4.6 <[email protected]>

src/agent/agent_loop.rs

@@ -682,7 +682,15 @@ impl Agent {
 
         // Convert SubmissionResult to response string
         match result? {
-            SubmissionResult::Response { content } => Ok(Some(content)),
+            SubmissionResult::Response { content } => {
+                // Suppress silent replies (e.g. from group chat "nothing to say" responses)
+                if crate::llm::is_silent_reply(&content) {
+                    tracing::debug!("Suppressing silent reply token");
+                    Ok(None)
+                } else {
+                    Ok(Some(content))
+                }
+            }
             SubmissionResult::Ok { message } => Ok(message),
             SubmissionResult::Error { message } => Ok(Some(format!("Error: {}", message))),
             SubmissionResult::Interrupted => Ok(Some("Interrupted.".into())),

src/agent/dispatcher.rs

@@ -40,9 +40,17 @@ impl Agent {
         thread_id: Uuid,
         initial_messages: Vec<ChatMessage>,
     ) -> Result<AgenticLoopResult, Error> {
+        // Detect group chat from channel metadata (needed before loading system prompt)
+        let is_group_chat = message
+            .metadata
+            .get("chat_type")
+            .and_then(|v| v.as_str())
+            .is_some_and(|t| t == "group" || t == "channel" || t == "supergroup");
+
         // Load workspace system prompt (identity files: AGENTS.md, SOUL.md, etc.)
+        // In group chats, MEMORY.md is excluded to prevent leaking personal context.
         let system_prompt = if let Some(ws) = self.workspace() {
-            match ws.system_prompt().await {
+            match ws.system_prompt_for_context(is_group_chat).await {
                 Ok(prompt) if !prompt.is_empty() => Some(prompt),
                 Ok(_) => None,
                 Err(e) => {
@@ -94,7 +102,10 @@ impl Agent {
             None
         };
 
-        let mut reasoning = Reasoning::new(self.llm().clone(), self.safety().clone());
+        let mut reasoning = Reasoning::new(self.llm().clone(), self.safety().clone())
+            .with_channel(message.channel.clone())
+            .with_model_name(self.llm().active_model_name())
+            .with_group_chat(is_group_chat);
         if let Some(prompt) = system_prompt {
             reasoning = reasoning.with_system_prompt(prompt);
         }