feat(#2109): harness-side idle watchdog to bail on anthropic api stall storms

hive-claude/src/error.rs

@@ -57,6 +57,14 @@ pub enum Error {
     #[error("waiting on claude failed: {0}")]
     Wait(#[source] std::io::Error),
 
+    /// The child produced no stdout for longer than the configured idle
+    /// window (`Config::idle_timeout`) and was killed. Indicative of an
+    /// Anthropic API stall (e.g. a multi-retry connection storm that goes
+    /// silent for minutes). Callers typically park briefly and retry, like
+    /// the rate-limit path.
+    #[error("claude idle timeout: no output for the configured window")]
+    IdleTimeout,
+
     /// claude exited non-zero and raised none of the recognized sentinels.
     /// `stderr_tail` is the last handful of stderr lines (empty if there were
     /// none), included so the caller can surface a real diagnostic.