heartbeat the matrix-accounts snapshot so as_of tracks daemon liveness

hive-matrix-mcp/src/accounts.rs

@@ -207,27 +207,67 @@ impl Registry {
     pub fn write_snapshot(&self, path: &Path) -> anyhow::Result<()> {
         write_accounts_snapshot(path, &self.list())
     }
+
+    /// Heartbeat the snapshot: rewrite it unconditionally so the file
+    /// mtime advances even when the account set is unchanged. The daemon
+    /// calls this on a timer (see `main`) so the dashboard's `as_of`
+    /// (derived from the file mtime) tracks real daemon liveness instead
+    /// of freezing at the boot-time write — a stalled mtime then means
+    /// the daemon is down, which the dashboard can render as stale/dimmed.
+    ///
+    /// # Errors
+    /// Propagates filesystem errors from the atomic write.
+    pub fn heartbeat_snapshot(&self, path: &Path) -> anyhow::Result<()> {
+        heartbeat_accounts_snapshot(path, &self.list())
+    }
 }
 
 /// Atomically write `accounts` as pretty-printed JSON to `path`
 /// (`<path>.tmp` + rename) so a dashboard reader never sees a partial
 /// file. Idempotent — skips the rewrite when the on-disk content already
-/// matches, keeping the mtime stable.
+/// matches, keeping the mtime stable. Used for the boot-time publish.
 ///
 /// The daemon rebuilds this file fresh on every boot (and is restarted
 /// by the `matrix-token*` path-watcher when a new account is
 /// provisioned), so the file lists exactly the accounts that restored at
-/// the last start. A reader wanting true real-time liveness should also
-/// confirm the daemon is running — a stale file otherwise reports the
-/// last-known-up set.
+/// the last start. Real-time liveness is conveyed by the file mtime,
+/// which the daemon advances on a timer via
+/// [`heartbeat_accounts_snapshot`] — a stalled mtime means the daemon is
+/// down, so a reader can treat an old snapshot as stale.
 ///
 /// # Errors
 /// Returns an error if the parent dir can't be created or the
 /// write/rename fails.
 pub fn write_accounts_snapshot(path: &Path, accounts: &[AccountStatus]) -> anyhow::Result<()> {
+    write_accounts_snapshot_inner(path, accounts, false)
+}
+
+/// Like [`write_accounts_snapshot`] but always rewrites (tmp + rename)
+/// even when the on-disk content is byte-identical, so the file mtime
+/// advances. The daemon calls this on a periodic heartbeat so the
+/// dashboard's `as_of` (the file mtime) reflects daemon liveness rather
+/// than freezing at the boot-time write.
+///
+/// # Errors
+/// Returns an error if the parent dir can't be created or the
+/// write/rename fails.
+pub fn heartbeat_accounts_snapshot(path: &Path, accounts: &[AccountStatus]) -> anyhow::Result<()> {
+    write_accounts_snapshot_inner(path, accounts, true)
+}
+
+/// Shared body for [`write_accounts_snapshot`] (idempotent) and
+/// [`heartbeat_accounts_snapshot`] (`force`). When `force` is false the
+/// rewrite is skipped if the on-disk content already matches, keeping the
+/// mtime stable; when true the tmp + rename always runs so the mtime
+/// advances.
+fn write_accounts_snapshot_inner(
+    path: &Path,
+    accounts: &[AccountStatus],
+    force: bool,
+) -> anyhow::Result<()> {
     let body =
         serde_json::to_string_pretty(accounts).expect("Vec<AccountStatus> is always serialisable");
-    if std::fs::read_to_string(path).ok().as_deref() == Some(body.as_str()) {
+    if !force && std::fs::read_to_string(path).ok().as_deref() == Some(body.as_str()) {
         return Ok(());
     }
     if let Some(parent) = path.parent() {
@@ -247,7 +287,7 @@ pub fn write_accounts_snapshot(path: &Path, accounts: &[AccountStatus]) -> anyho
 
 #[cfg(test)]
 mod tests {
-    use super::{AccountStatus, write_accounts_snapshot};
+    use super::{AccountStatus, heartbeat_accounts_snapshot, write_accounts_snapshot};
 
     fn sample() -> Vec<AccountStatus> {
         vec![
@@ -319,4 +359,36 @@ mod tests {
 
         std::fs::remove_dir_all(&dir).ok();
     }
+
+    #[test]
+    fn heartbeat_advances_mtime_even_when_unchanged() {
+        let dir = std::env::temp_dir().join(format!(
+            "hh-acct-hb-{}-{}",
+            std::process::id(),
+            std::time::SystemTime::now()
+                .duration_since(std::time::UNIX_EPOCH)
+                .unwrap()
+                .as_nanos()
+        ));
+        std::fs::create_dir_all(&dir).unwrap();
+        let path = dir.join("matrix-accounts.json");
+
+        write_accounts_snapshot(&path, &sample()).unwrap();
+        let mtime1 = std::fs::metadata(&path).unwrap().modified().unwrap();
+        // The heartbeat must rewrite (tmp + rename) even when the content
+        // is byte-identical, so the mtime advances and the dashboard reads
+        // a fresh `as_of`. Small sleep so the new mtime is strictly later
+        // than the first (tmpfs/ext4 have sub-second mtime resolution).
+        std::thread::sleep(std::time::Duration::from_millis(20));
+        heartbeat_accounts_snapshot(&path, &sample()).unwrap();
+        let mtime2 = std::fs::metadata(&path).unwrap().modified().unwrap();
+        assert!(mtime2 > mtime1, "heartbeat should advance mtime");
+        // Content is still the same shape, and no leftover temp file.
+        let written = std::fs::read_to_string(&path).unwrap();
+        let parsed: serde_json::Value = serde_json::from_str(&written).unwrap();
+        assert_eq!(parsed[0]["name"], "main");
+        assert!(!path.with_extension("json.tmp").exists());
+
+        std::fs::remove_dir_all(&dir).ok();
+    }
 }