Route HEARTBEAT writes to workspace DB and broadcast notifications

- Add dedicated "heartbeat" target in memory_write tool so the LLM
  routes HEARTBEAT.md writes to the database instead of the filesystem
- Update tool description to clarify it's database-backed storage
- Broadcast heartbeat notifications to all channels when no explicit
  notify target is configured, instead of silently logging them

Co-Authored-By: Claude Opus 4.6 <[email protected]>

src/agent/agent_loop.rs

@@ -212,11 +212,19 @@ impl Agent {
                                     }
                                 }
                                 _ => {
-                                    // No target configured, just log
-                                    tracing::info!(
-                                        "Heartbeat notification (no target configured): {}",
-                                        &response.content
-                                    );
+                                    // No explicit target, broadcast to all channels
+                                    // for the default user so notifications actually
+                                    // reach someone instead of vanishing into logs.
+                                    let results = channels.broadcast_all("default", response).await;
+                                    for (ch, result) in results {
+                                        if let Err(e) = result {
+                                            tracing::warn!(
+                                                "Failed to broadcast heartbeat to {}: {}",
+                                                ch,
+                                                e
+                                            );
+                                        }
+                                    }
                                 }
                             }
                         }

src/tools/builtin/memory.rs

@@ -133,10 +133,11 @@ impl Tool for MemoryWriteTool {
     }
 
     fn description(&self) -> &str {
-        "Write to persistent memory. Use for important facts, decisions, preferences, \
-         or lessons learned that should be remembered across sessions. Use 'memory' target \
-         for curated long-term facts, 'daily_log' for timestamped session notes, or \
-         provide a custom path for arbitrary file creation."
+        "Write to persistent memory (database-backed, NOT the local filesystem). \
+         Use for important facts, decisions, preferences, or lessons learned that should \
+         be remembered across sessions. Targets: 'memory' for curated long-term facts, \
+         'daily_log' for timestamped session notes, 'heartbeat' for the periodic \
+         checklist (HEARTBEAT.md), or provide a custom path for arbitrary file creation."
     }
 
     fn parameters_schema(&self) -> serde_json::Value {
@@ -149,7 +150,7 @@ impl Tool for MemoryWriteTool {
                 },
                 "target": {
                     "type": "string",
-                    "description": "Where to write: 'memory' for MEMORY.md, 'daily_log' for today's log, or a path like 'projects/alpha/notes.md'",
+                    "description": "Where to write: 'memory' for MEMORY.md, 'daily_log' for today's log, 'heartbeat' for HEARTBEAT.md checklist, or a path like 'projects/alpha/notes.md'",
                     "default": "daily_log"
                 },
                 "append": {
@@ -214,6 +215,20 @@ impl Tool for MemoryWriteTool {
                     .map_err(|e| ToolError::ExecutionFailed(format!("Write failed: {}", e)))?;
                 format!("daily/{}.md", chrono::Utc::now().format("%Y-%m-%d"))
             }
+            "heartbeat" => {
+                if append {
+                    self.workspace
+                        .append(paths::HEARTBEAT, content)
+                        .await
+                        .map_err(|e| ToolError::ExecutionFailed(format!("Write failed: {}", e)))?;
+                } else {
+                    self.workspace
+                        .write(paths::HEARTBEAT, content)
+                        .await
+                        .map_err(|e| ToolError::ExecutionFailed(format!("Write failed: {}", e)))?;
+                }
+                paths::HEARTBEAT.to_string()
+            }
             path => {
                 if append {
                     self.workspace