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/core/src/session/session.rs

@@ -966,6 +966,8 @@ impl Session {
             for contributor in extensions.thread_lifecycle_contributors() {
                 contributor.on_thread_start(codex_extension_api::ThreadStartInput {
                     config: config.as_ref(),
+                    session_source: &session_configuration.session_source,
+                    persistent_thread_state_available: state_db_ctx.is_some(),
                     session_store: &session_extension_data,
                     thread_store: &thread_extension_data,
                 }).await;

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.

codex-rs/ext/goal/tests/goal_extension_backend.rs

@@ -889,10 +889,13 @@ async fn installed_tools(
     let registry = builder.build();
     let session_store = ExtensionData::new("session-1");
     let thread_store = ExtensionData::new(thread_id.to_string());
+    let session_source = SessionSource::Cli;
     for contributor in registry.thread_lifecycle_contributors() {
         contributor
             .on_thread_start(ThreadStartInput {
                 config: &(),
+                session_source: &session_source,
+                persistent_thread_state_available: true,
                 session_store: &session_store,
                 thread_store: &thread_store,
             })
@@ -930,10 +933,13 @@ impl GoalExtensionHarness {
         let registry = builder.build();
         let session_store = ExtensionData::new("session-1");
         let thread_store = ExtensionData::new(thread_id.to_string());
+        let session_source = SessionSource::Cli;
         for contributor in registry.thread_lifecycle_contributors() {
             contributor
                 .on_thread_start(ThreadStartInput {
                     config: &(),
+                    session_source: &session_source,
+                    persistent_thread_state_available: true,
                     session_store: &session_store,
                     thread_store: &thread_store,
                 })