Snapshot resolved settings for each model step (#40651)

## Why

Thread settings can change while a turn is running, and delegated review or
compaction steps can select a different model. Each request needs a consistent
set of settings resolved against the model that will execute it.

## What changed

- Capture immutable resolved settings for each model step, including model
  metadata, reasoning options, service tier, approvals, and personality.
- Keep in-flight steps on their captured settings while applying thread updates
  to subsequent work.
- Resolve inherited reasoning summaries and filter service tiers against the
  selected model and feature configuration for review and compaction steps.

## Testing

Added coverage for settings updates during paused turns, model changes,
previous-model compaction, review-model defaults, and service-tier filtering.

GitOrigin-RevId: fca4b3b305379f1bf26a5cac75ee0dd1747ac1f6

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

@@ -766,7 +766,7 @@ async fn review_guardian_mcp_elicitation(
             || crate::connectors::mcp_approvals_reviewer_from_layers(
                 &mcp_config.config_layer_stack,
                 ApprovalsReviewer::AutoReview,
-                Some(turn_context.model_info.slug.as_str()),
+                Some(turn_context.model_info().slug.as_str()),
                 request.server_name.as_str(),
                 connector_id,
             ) != ApprovalsReviewer::AutoReview
@@ -806,7 +806,7 @@ async fn review_guardian_mcp_elicitation(
                 | ReviewDecision::Abort
         )
         .then(|| {
-            mcp_elicitation_response_from_guardian_decision(decision, &turn_context.model_info)
+            mcp_elicitation_response_from_guardian_decision(decision, turn_context.model_info())
         }));
     }
 
@@ -844,7 +844,7 @@ async fn review_guardian_mcp_elicitation(
     let approvals_reviewer = crate::connectors::mcp_approvals_reviewer_from_layers(
         &mcp_config.config_layer_stack,
         mcp_config.approvals_reviewer,
-        Some(turn_context.model_info.slug.as_str()),
+        Some(turn_context.model_info().slug.as_str()),
         request.server_name.as_str(),
         elicitation_connector_id(&request.elicitation),
     );
@@ -882,7 +882,7 @@ async fn review_guardian_mcp_elicitation(
     .await;
     Ok(Some(mcp_elicitation_response_from_guardian_decision(
         decision,
-        &turn_context.model_info,
+        turn_context.model_info(),
     )))
 }