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

hive-claude/src/config.rs

@@ -1,6 +1,7 @@
 //! Invocation config: how to build one `claude --print` command line.
 
 use std::path::PathBuf;
+use std::time::Duration;
 
 /// How a run attaches to a claude session — the low-level session flag. Kept
 /// separate from [`Config`] so one config can drive resume + create +
@@ -56,4 +57,11 @@ pub struct Config {
     pub extra_args: Vec<String>,
     /// Program to spawn. `None` defaults to `claude` (resolved on `PATH`).
     pub program: Option<String>,
+    /// Idle watchdog: kill the child and return [`crate::Error::IdleTimeout`]
+    /// if no stdout line arrives for this long. The timer resets on every
+    /// stdout line, so a large/slow but still-streaming turn is never cut;
+    /// only complete output silence trips it. `None` waits indefinitely.
+    /// The driver stays policy-free — the caller decides the window (and
+    /// whether to read it from the environment).
+    pub idle_timeout: Option<Duration>,
 }