Source Guardian REPL policy from model metadata (#41919)

## What changed

- Add `auto_review.node_repl_policy` to model messages for `node_repl` and `cua_repl` reviews.
- Use the reviewer model's configured policy, falling back to the bundled policy when the field is absent and skipping injection when it is explicitly empty.
- Include the effective policy in Guardian session reuse checks and reject unsafe parent-model fallback transitions that would change it.

## Testing

- Cover catalog, bundled, and explicitly empty policies across Node and CUA review paths.
- Verify that policy changes invalidate cached reviewer sessions and incompatible fallback transitions.

GitOrigin-RevId: 51c0bdfed9b464091b6eb47d91ca5a0990d7a315

codex-rs/protocol/src/openai_models.rs

@@ -623,6 +623,9 @@ pub struct CollaborationModeMessages {
 pub struct AutoReviewMessages {
     pub policy: Option<String>,
     pub policy_template: Option<String>,
+    /// Extra developer policy for `node_repl` and `cua_repl` reviews.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub node_repl_policy: Option<String>,
     pub rejection_instructions: Option<String>,
     pub timeout_instructions: Option<String>,
 }
@@ -1139,6 +1142,7 @@ mod tests {
                 "auto_review": {
                     "policy": "policy",
                     "policy_template": "",
+                    "node_repl_policy": "",
                     "rejection_instructions": "",
                     "timeout_instructions": ""
                 }
@@ -1151,6 +1155,7 @@ mod tests {
             Some(AutoReviewMessages {
                 policy: Some("policy".to_string()),
                 policy_template: None,
+                node_repl_policy: None,
                 rejection_instructions: None,
                 timeout_instructions: None,
             })
@@ -1160,6 +1165,7 @@ mod tests {
             Some(AutoReviewMessages {
                 policy: Some("policy".to_string()),
                 policy_template: Some(String::new()),
+                node_repl_policy: Some(String::new()),
                 rejection_instructions: Some(String::new()),
                 timeout_instructions: Some(String::new()),
             })
@@ -1559,6 +1565,7 @@ mod tests {
             auto_review: Some(AutoReviewMessages {
                 policy: Some("policy".to_string()),
                 policy_template: None,
+                node_repl_policy: None,
                 rejection_instructions: Some("rejection instructions".to_string()),
                 timeout_instructions: Some("timeout instructions".to_string()),
             }),