Preserve Guardian history across thread reconstruction (#42065)

## Why

Guardian review evidence must remain available after a compacted thread is resumed or forked, while rolled-back or parent-local evidence must not grant authorization in a different context.

## What changed

- Store the bounded, model-invisible Guardian transcript alongside compacted rollout history and restore it from the newest surviving checkpoint during replay.
- Trim Guardian history at rollback boundaries, clearing it when the boundary has already been evicted.
- Preserve the checkpoint for user-initiated forks, but remove it when spawning a subagent so parent review evidence is not inherited.
- Keep the new rollout field optional for compatibility with existing compacted records and legacy readers.

## Testing

- Cover Guardian history across compaction, restart, paginated and pathless stores, user forks, rollback, bounded replay, serialization, and subagent forks.

GitOrigin-RevId: 6ab076d5e0c3aac4d6a41ebd50ba2b200c90213e

codex-rs/app-server-protocol/src/protocol/thread_history.rs

@@ -4056,6 +4056,7 @@ mod tests {
             RolloutItem::Compacted(CompactedItem {
                 message: String::new(),
                 replacement_history: None,
+                guardian_history: None,
                 mcp_resource_origins: None,
                 window_number: None,
                 first_window_id: None,

codex-rs/app-server-protocol/src/protocol/thread_history_projection_tests.rs

@@ -200,6 +200,7 @@ fn ignores_legacy_abort_without_turn_id_and_context_only_records() {
     let compacted = project(RolloutItem::Compacted(CompactedItem {
         message: String::new(),
         replacement_history: None,
+        guardian_history: None,
         mcp_resource_origins: None,
         window_number: None,
         first_window_id: None,