fix(maestro): always probe tmux during recovery

#164 skipped the tmux probe whenever the stored boot id differed from the
current one, assuming a changed boot id proves the tmux server is gone. It
does not: a restored state directory, a VM or container snapshot rollback,
or a truncated boot_id file all change it while tmux keeps running with
live sessions. Every one of those sessions was then registered Dormant and
stranded — resume respawns `maestro-<id>`, which collides with the name
tmux still holds, so it failed 502 forever.

Recovery now always runs `tmux list-sessions`, the single source of truth
for liveness the rest of the daemon assumes. The boot id keeps its other
job: telling a reboot from a restart in recovery's log.

The #164 test asserted the old behaviour with tmux still alive, so it is
replaced by one asserting the session is adopted Running, plus one covering
a real reboot — boot id changed and the tmux server dead — still going
dormant.

Refs #174

crates/maestro-daemon/src/boot_id.rs

@@ -2,10 +2,13 @@
 //!
 //! `/proc/sys/kernel/random/boot_id` is fixed for the life of the kernel and
 //! changes on every boot. [`SessionManager::recover`] compares it against the
-//! value it stored on the previous run: a difference means every session from
-//! before is provably dead, so the tmux probe can be skipped and those
-//! sessions registered dormant directly instead of relying on tmux reporting
-//! an empty list.
+//! value it stored on the previous run and logs which of the two it was.
+//!
+//! It does not decide liveness (#174). A boot id changes without the tmux
+//! server dying whenever the state directory is restored, a VM or container
+//! snapshot is rolled back, or the `boot_id` file is truncated — so recovery
+//! always probes `tmux list-sessions` and the boot id only says whether a
+//! server that did not answer is coming back.
 
 use std::path::Path;
 

crates/maestro-daemon/src/session.rs

@@ -847,20 +847,20 @@ impl SessionManager {
     /// that no longer exists are still adopted — the spec does not require
     /// us to repair them.
     ///
-    /// #164: when the kernel's boot id has changed since the last run, the
-    /// tmux probe below is skipped entirely — a reboot kills the tmux server,
-    /// so every previous session is already dead and there is nothing tmux
-    /// could truthfully adopt. [`Self::register_dormant`] then registers all
-    /// of them directly.
+    /// #164/#174: the kernel's boot id says whether the host rebooted since
+    /// the last run, but it never decides which sessions are alive —
+    /// `tmux list-sessions` does, always, which is what the rest of the
+    /// daemon assumes. A boot id can change without the tmux server dying
+    /// (a restored state directory, a VM or container snapshot restore, a
+    /// truncated `boot_id` file); skipping the probe then registered every
+    /// live session `Dormant`, and resume could never bring one back because
+    /// the tmux name was still taken. The boot id is now only a signal that a
+    /// tmux server which did not answer is not coming back, and it names
+    /// itself in recovery's log.
     pub async fn recover(&self) -> Result<usize, SessionError> {
         tokio::fs::create_dir_all(&self.inner.fifo_dir).await?;
         let rebooted = self.check_boot_id().await;
-        let live = if rebooted {
-            // #164: every session from the previous boot is provably dead —
-            // no tmux server survives a reboot — so there is nothing to gain
-            // from asking it and no session it could honestly report back.
-            Vec::new()
-        } else {
+        let live = {
             let tmux = self.inner.tmux.clone();
             tmux_blocking(move || tmux.list_sessions()).await?
         };
@@ -940,7 +940,9 @@ impl SessionManager {
     ///
     /// A missing stored value (first run) or an unreadable current one
     /// (non-Linux, restricted `/proc`, unwired in this build) both read as
-    /// "no reboot", which is today's behaviour: fall back to probing tmux.
+    /// "no reboot". Either way the tmux probe runs (#174): the answer only
+    /// tells recovery whether a tmux server that did not answer is coming
+    /// back, never which sessions are alive.
     async fn check_boot_id(&self) -> bool {
         let Some(cfg) = &self.inner.boot_id else {
             return false;
@@ -987,7 +989,8 @@ impl SessionManager {
     /// `rebooted` (#164) only changes what gets logged: a detected reboot
     /// names the count even when it is zero, so the operator sees that
     /// recovery told a reboot from a restart instead of a log that stays
-    /// silent either way.
+    /// silent either way. It never decides membership — everything here got
+    /// here by tmux not holding it (#174).
     async fn register_dormant(&self, rebooted: bool) {
         let stored = match self.inner.sidecar.load_all() {
             Ok(stored) => stored,

crates/maestro-daemon/tests/session_manager.rs

@@ -326,12 +326,14 @@ fn revive_with_boot_id(
     )
 }
 
-/// #164: a changed boot id means every session from the previous boot is
-/// already dead, so recovery must not trust tmux to say so — it skips the
-/// probe outright. Proven by leaving the tmux session alive: if the probe
-/// ran, it would come back `Running`, not `Dormant`.
+/// #174: a boot id can change without the tmux server dying — a restored
+/// state directory, a VM or container snapshot restore, a truncated
+/// `boot_id` file. `tmux list-sessions` stays the single source of truth for
+/// liveness, so a session tmux still holds is adopted `Running` no matter
+/// what the boot id says. Registering it dormant instead stranded it: resume
+/// would collide with the tmux name still in use and fail forever.
 #[tokio::test]
-async fn recover_skips_tmux_probe_when_boot_id_changed() {
+async fn recover_adopts_live_session_when_boot_id_changed() {
     let fx = DaemonFixture::new();
     let cwd = TempDir::new().unwrap();
     let s = fx
@@ -349,15 +351,15 @@ async fn recover_skips_tmux_probe_when_boot_id_changed() {
     let boot_id_path = fx.state_dir.path().join("boot_id");
     std::fs::write(&boot_id_path, "previous-boot").unwrap();
 
-    // tmux session is still alive — a probe would find it if one ran.
+    // tmux session is still alive: the probe runs and finds it.
     let revived = revive_with_boot_id(&fx, boot_id_path.clone(), Some("current-boot"));
     let adopted = revived.recover().await.expect("recover");
-    assert_eq!(adopted, 0, "reboot detected: nothing adopted live");
+    assert_eq!(adopted, 1, "tmux still holds the session; adopt it");
 
     let snap = revived.snapshot().await;
     assert_eq!(snap.len(), 1);
     assert_eq!(snap[0].id, s.id);
-    assert_eq!(snap[0].status, SessionStatus::Dormant);
+    assert_eq!(snap[0].status, SessionStatus::Running);
 
     // The current boot id is now the stored one, for the next comparison.
     assert_eq!(
@@ -366,6 +368,38 @@ async fn recover_skips_tmux_probe_when_boot_id_changed() {
     );
 }
 
+/// #164, still true after #174: a real reboot takes the tmux server with it,
+/// so the probe comes back empty and every sidecar is registered dormant.
+#[tokio::test]
+async fn recover_registers_dormant_when_boot_id_changed_and_tmux_gone() {
+    let fx = DaemonFixture::new();
+    let cwd = TempDir::new().unwrap();
+    let s = fx
+        .manager
+        .create(CreateSessionRequest {
+            cwd: cwd.path().to_path_buf(),
+            command: "sleep 30".into(),
+            env: HashMap::new(),
+            metadata: HashMap::new(),
+            worktree: None,
+        })
+        .await
+        .expect("create");
+
+    let boot_id_path = fx.state_dir.path().join("boot_id");
+    std::fs::write(&boot_id_path, "previous-boot").unwrap();
+    fx.tmux.tmux.kill_server().expect("kill tmux server");
+
+    let revived = revive_with_boot_id(&fx, boot_id_path, Some("current-boot"));
+    let adopted = revived.recover().await.expect("recover");
+    assert_eq!(adopted, 0, "no tmux server survived the reboot");
+
+    let snap = revived.snapshot().await;
+    assert_eq!(snap.len(), 1);
+    assert_eq!(snap[0].id, s.id);
+    assert_eq!(snap[0].status, SessionStatus::Dormant);
+}
+
 /// #164: an unchanged boot id is a plain restart — recovery probes tmux as
 /// before and adopts the still-live session `Running`.
 #[tokio::test]

docs/RESTART.md

@@ -75,7 +75,13 @@ A daemon restart leaves tmux alone, so recovery re-adopts every
 beyond the reconnect above.
 
 A **host reboot** is different: it kills the tmux server, so there is nothing
-to adopt while every session's sidecar is still on disk. Recovery makes a
+to adopt while every session's sidecar is still on disk. Recovery always asks
+tmux — `tmux list-sessions` is the single source of truth for liveness, and the
+kernel's `boot_id` only tells a reboot from a restart in the log (#164, #174).
+A boot id changes without the tmux server dying whenever the state directory is
+restored, a VM or container snapshot is rolled back, or the `boot_id` file is
+truncated; a session tmux still holds is adopted `Running` in every one of
+those cases. Recovery makes a
 second pass over those sidecars and registers each as a `Dormant` session
 (#162) — id, name, cwd, command, worktree and `created_at` intact. A dormant
 session has no pane and no PTY bridge: it cannot be attached to, typed into or