Add step-scoped data to extension contributors (#34525)

## What changed

- Add an `ExtensionData` store to each `StepContext`.
- Pass the step store to context, world-state, turn-input, and tool contributors so extensions can use capabilities bound to the current sampling step.
- Preserve the captured step context when rebuilding initial context during compaction.

GitOrigin-RevId: 51f3105d3a793f60534f122f9be8247c131c2ca5

codex-rs/core/src/tools/router_tests.rs

@@ -43,6 +43,7 @@ impl codex_extension_api::ToolContributor for ExtensionEchoContributor {
         &self,
         _session_store: &ExtensionData,
         _thread_store: &ExtensionData,
+        _step_store: &ExtensionData,
     ) -> Vec<Arc<dyn ToolExecutor<ExtensionToolCall>>> {
         vec![Arc::new(ExtensionEchoExecutor)]
     }
@@ -390,7 +391,7 @@ async fn extension_tool_executors_are_model_visible_and_dispatchable() -> anyhow
         ToolRouterParams {
             tool_suggest_candidates: None,
             tool_runtimes: Vec::new(),
-            extension_tool_executors: extension_tool_executors(&session),
+            extension_tool_executors: extension_tool_executors(&session, step_context.as_ref()),
             dynamic_tools: turn.dynamic_tools.as_slice(),
         },
         &Default::default(),