Require automatic review for high-risk Guardian v2 actions (#38569)

## What changed

- Add a thread-scoped extension API for requesting automatic review, resolving
  multiple contributors to the strongest requirement.
- Have Guardian v2 request automatic review when it is enabled and the latest
  `action_risk` score is at least `0.8`.
- Honor extension review requirements across tool approvals, MCP elicitation,
  and remote execution while preserving host configuration and managed-policy
  constraints.

## Testing

- Cover contributor registration and requirement resolution.
- Verify Guardian v2 requests review at the threshold, returns to the default
  below it, and does not affect threads where the extension is disabled.
- Exercise extension-requested strict review with a remote model override.

GitOrigin-RevId: 6329fc23585d5cc7173c39bb9952c3109ec3884b

codex-rs/ext/extension-api/src/lib.rs

@@ -35,6 +35,8 @@ pub use codex_tools::TurnItemEmissionFuture;
 pub use codex_tools::TurnItemEmitter;
 pub use codex_tools::parse_tool_input_schema;
 pub use codex_tools::parse_tool_input_schema_without_compaction;
+pub use contributors::ApprovalPolicyContributor;
+pub use contributors::ApprovalRequirement;
 pub use contributors::ApprovalReviewContributor;
 pub use contributors::ConfigContributor;
 pub use contributors::ContextContributor;