added parking_lot mutex

Cargo.toml

@@ -22,6 +22,11 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 thiserror = "2"
 anyhow = "1"
+# Non-poisoning mutexes. A handler that panics while holding a lock must not
+# wedge every later acquisition of it: `Workers` catches the unwind to keep the
+# pool alive, and `std::sync::Mutex` would defeat that by poisoning the state
+# the recovered worker needs.
+parking_lot = "0.12"
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 directories = "5"