heartbeat the matrix-accounts snapshot so as_of tracks daemon liveness

hive-matrix-mcp/src/main.rs

@@ -46,6 +46,12 @@ use accounts::{AccountCfg, Registry};
 /// `select_all`) rather than `tokio::spawn`/`JoinSet`.
 type SyncLoop = std::pin::Pin<Box<dyn std::future::Future<Output = Result<()>>>>;
 
+/// How often the daemon rewrites the accounts snapshot to advance its
+/// mtime, so the dashboard's `as_of` tracks daemon liveness. 30s keeps
+/// the staleness window small while the rewrite cost (one tmp + rename of
+/// a tiny file) is negligible.
+const ACCOUNTS_HEARTBEAT_SECS: u64 = 30;
+
 #[tokio::main]
 async fn main() -> Result<()> {
     tracing_subscriber::fmt()
@@ -116,6 +122,26 @@ async fn main() -> Result<()> {
     // sync loops so the MCP bridge can connect as soon as the first
     // claude turn fires.
     let registry = Arc::new(registry);
+
+    // Heartbeat: periodically rewrite the accounts snapshot so its mtime
+    // advances while the daemon lives. The dashboard derives `as_of` from
+    // the file mtime, so a stalled mtime now means the daemon is down —
+    // which lets the dashboard dim accounts whose snapshot is stale rather
+    // than reporting the boot-time set forever (BE-4 follow-up).
+    let hb_registry = Arc::clone(&registry);
+    tokio::spawn(async move {
+        let mut tick =
+            tokio::time::interval(std::time::Duration::from_secs(ACCOUNTS_HEARTBEAT_SECS));
+        tick.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Skip);
+        let path = paths::accounts_file();
+        loop {
+            tick.tick().await;
+            if let Err(e) = hb_registry.heartbeat_snapshot(&path) {
+                tracing::warn!(error = %format!("{e:#}"), "matrix-accounts heartbeat write failed");
+            }
+        }
+    });
+
     let socket_listener = mcp_socket.clone();
     tokio::spawn(async move {
         if let Err(e) = socket::serve(&socket_listener, registry).await {