Thread Guardian cache key through session (#24895)

Split from the Guardian prompt cache key change. This PR only updates
codex-rs/core/src/session/session.rs. Validation was not run per
request; this branch is expected to rely on the companion split PRs.

codex-rs/core/src/session/session.rs

@@ -1034,6 +1034,12 @@ impl Session {
                     config.features.enabled(Feature::RuntimeMetrics),
                     Self::build_model_client_beta_features_header(config.as_ref()),
                     attestation_provider,
+                )
+                .with_prompt_cache_key_override(
+                    crate::guardian::prompt_cache_key_override_for_review_session(
+                        &session_configuration.session_source,
+                        session_configuration.forked_from_thread_id,
+                    ),
                 ),
                 code_mode_service: crate::tools::code_mode::CodeModeService::new(),
                 environment_manager,