Log panics through tracing so they reach the rolling log file (#241)

Rust's default panic hook writes only to stderr, so panics never reached
the rolling file appender (logs/beacon.log.*), making post-mortem
debugging from log files impossible.

Install a panic hook in async_main() (right after setup_tracing) that
routes panics through `tracing` at ERROR level via the tracing-panic
crate, while chaining the default hook to preserve stderr output. Panics
now appear in both stdout and the rolling log file with message,
location, and (when RUST_BACKTRACE is set) a backtrace.

Closes #239

Author: robinskil

Cargo.lock

@@ -33,6 +33,7 @@ uuid = { version = "1.16.0" }
 tracing = { workspace = true}
 tracing-subscriber = { workspace = true}
 tracing-appender = { workspace = true}
+tracing-panic = "0.1"
 tonic = "0.14.1"
 prost = "0.14.1"
 

beacon-api/Cargo.toml

@@ -39,6 +39,7 @@ fn main() -> anyhow::Result<()> {
 /// Initializes shared services and starts all configured API transports.
 async fn async_main() -> anyhow::Result<()> {
     setup_tracing();
+    install_panic_hook();
 
     tracing::info!("Beacon v{}", BEACON_VERSION);
     let beacon_runtime = Arc::new(beacon_core::runtime::Runtime::new().await?);
@@ -81,6 +82,16 @@ async fn serve_http(router: ::axum::Router, addr: std::net::SocketAddr) -> anyho
     Ok(())
 }
 
+/// Routes panics through `tracing` (so they land in the rolling log file) while
+/// preserving the default hook's stderr output.
+fn install_panic_hook() {
+    let default_hook = std::panic::take_hook();
+    std::panic::set_hook(Box::new(move |info| {
+        tracing_panic::panic_hook(info); // ERROR event -> stdout + rolling log file
+        default_hook(info); // preserve default stderr output
+    }));
+}
+
 /// Configures stdout and rolling-file tracing subscribers for the API process.
 fn setup_tracing() {
     let file_appender = tracing_appender::rolling::daily("logs", "beacon.log");