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/multi_agents.rs

@@ -73,7 +73,7 @@ pub(super) fn usage_hint_text(
     }
 
     let catalog = turn_context
-        .model_info
+        .model_info()
         .model_messages
         .as_ref()
         .and_then(|messages| messages.multi_agent.as_ref())
@@ -148,7 +148,7 @@ pub(crate) fn effective_multi_agent_mode(turn_context: &TurnContext) -> Option<M
     }
 
     let catalog_mode = turn_context
-        .model_info
+        .model_info()
         .model_messages
         .as_ref()
         .and_then(|messages| messages.multi_agent.as_ref())