Add thread start contributor facts (#24915)

Summary: add session source and persistent-state availability to
ThreadStartInput; populate them from session init; update existing goal
test harness constructors. Tests: just fmt; git diff --check. No full
tests or clippy run per request.

codex-rs/ext/extension-api/src/contributors/thread_lifecycle.rs

@@ -1,9 +1,14 @@
 use crate::ExtensionData;
+use codex_protocol::protocol::SessionSource;
 
 /// Input supplied when the host starts a runtime for a thread.
 pub struct ThreadStartInput<'a, C> {
     /// Host configuration visible at thread start.
     pub config: &'a C,
+    /// Source that created the session for this thread.
+    pub session_source: &'a SessionSource,
+    /// Whether persistent thread-scoped state is available for this thread.
+    pub persistent_thread_state_available: bool,
     /// Store scoped to the host session runtime.
     pub session_store: &'a ExtensionData,
     /// Store scoped to this thread runtime.