Explain active Domain maintenance contention

crates/lazaret-client/src/state.rs

@@ -50,7 +50,13 @@ pub fn run_command(command: StateCommand) -> Result<i32, Box<dyn std::error::Err
         return Err("reset target is not an exact configured persistent container path".into());
     }
     let root = configuration.persistent_domain_root().open_authority()?;
-    let lock = try_exclusive_flock(open_private_domain_lock(&root)?)?;
+    let lock = match try_exclusive_flock(open_private_domain_lock(&root)?) {
+        Ok(lock) => lock,
+        Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+            return Err("Domain state is busy; exit active Lazaret sessions or wait for another maintenance command to finish, then retry".into());
+        }
+        Err(error) => return Err(error.into()),
+    };
     let database = match openat2(
         root.as_fd(),
         "domain.redb",

crates/lazaret-client/tests/state_cli.rs

@@ -1,5 +1,7 @@
 use std::fs;
 
+use lazaret_linux::filesystem::try_exclusive_flock;
+
 #[allow(clippy::disallowed_methods, clippy::disallowed_types)]
 #[test]
 fn machine_and_human_discovery_are_versioned_and_content_free() {
@@ -42,6 +44,35 @@ fn reset_refuses_an_arbitrary_container_or_host_path_before_state_access() {
     );
 }
 
+#[allow(clippy::disallowed_methods, clippy::disallowed_types)]
+#[test]
+fn active_domain_reports_actionable_maintenance_contention() {
+    let fixture = Fixture::new();
+    assert!(fixture.command("list").output().unwrap().status.success());
+    let lock = try_exclusive_flock(
+        fs::OpenOptions::new()
+            .read(true)
+            .write(true)
+            .open(fixture.domain_root().join("domain.lock"))
+            .unwrap(),
+    )
+    .unwrap();
+
+    let active = fixture.command("verify").output().unwrap();
+    assert!(!active.status.success());
+    assert!(String::from_utf8_lossy(&active.stderr).contains(
+        "Domain state is busy; exit active Lazaret sessions or wait for another maintenance command to finish, then retry"
+    ));
+
+    drop(lock);
+    let inactive = fixture.command("verify").output().unwrap();
+    assert!(
+        inactive.status.success(),
+        "{}",
+        String::from_utf8_lossy(&inactive.stderr)
+    );
+}
+
 #[allow(clippy::disallowed_methods, clippy::disallowed_types)]
 #[test]
 fn missing_store_succeeds_only_when_the_complete_state_anchor_is_absent() {