Skip Git enrichment for prewarm and Guardian turns (#34728)

## Why

Startup prewarms and Guardian review sessions do not need workspace Git metadata. Collecting it for those requests performs redundant work, while user turns still need a fresh view of the repository.

## What changed

- Add a per-session Git enrichment policy.
- Skip enrichment for startup prewarm, preview, and Guardian review turns.
- Keep fresh enrichment enabled for regular sessions and one-shot delegated turns.

## Testing

- Cover prewarm and Guardian requests omitting workspace metadata while subsequent user turns observe repository changes.
- Cover concurrent repositories and worktrees retaining distinct metadata.
- Verify concurrent enrichment is coalesced and canceled enrichment can be retried.

GitOrigin-RevId: 4a68615288bb568c75f2e487d9c0776e3e80f191

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

@@ -673,6 +673,7 @@ impl Session {
             session_configuration,
             final_output_json_schema,
             TurnMultiAgentRuntime::ResolveAndStore,
+            self.git_enrichment_policy,
         )
         .await
     }
@@ -687,6 +688,7 @@ impl Session {
             session_configuration,
             /*final_output_json_schema*/ None,
             TurnMultiAgentRuntime::Preview,
+            GitEnrichmentPolicy::Skip,
         )
         .await
     }
@@ -698,6 +700,7 @@ impl Session {
         session_configuration: SessionConfiguration,
         final_output_json_schema: Option<Option<Value>>,
         multi_agent_runtime: TurnMultiAgentRuntime,
+        git_enrichment_policy: GitEnrichmentPolicy,
     ) -> Arc<TurnContext> {
         let turn_environments = self.services.turn_environments.snapshot().await;
         let primary_turn_environment = turn_environments.primary();
@@ -792,10 +795,11 @@ impl Session {
             turn_context.final_output_json_schema = final_schema;
         }
         let turn_context = Arc::new(turn_context);
-        if turn_context
-            .environments
-            .single_local_environment_cwd()
-            .is_some()
+        if git_enrichment_policy == GitEnrichmentPolicy::Fresh
+            && turn_context
+                .environments
+                .single_local_environment_cwd()
+                .is_some()
         {
             turn_context.turn_metadata_state.spawn_git_enrichment_task();
         }