Make Guardian v2 parent compaction reuse configurable (#39691)

## What changed

- Add `features.guardianv2.reuse_parent_compaction`, defaulting to `true` to preserve existing behavior.
- When disabled, omit parent compaction items from Guardian v2 contributor requests.
- Cover configuration parsing and disabled-reuse request construction.

GitOrigin-RevId: 0cf7c0ac7a2567c9f73a3f9724df6f6a6170e995

codex-rs/features/src/feature_configs.rs

@@ -139,6 +139,8 @@ pub struct GuardianV2ConfigToml {
     #[schemars(range(min = 100, max = 100000))]
     pub max_classifier_instruction_tokens: Option<usize>,
     #[serde(skip_serializing_if = "Option::is_none")]
+    pub reuse_parent_compaction: Option<bool>,
+    #[serde(skip_serializing_if = "Option::is_none")]
     #[schemars(range(min = 100, max = 100000))]
     pub max_parent_compaction_tokens: Option<usize>,
     #[serde(skip_serializing_if = "Option::is_none")]

codex-rs/features/src/tests.rs

@@ -160,6 +160,7 @@ max_tool_call_lag = 2
 reasoning_effort = "minimal"
 max_action_tokens = 512
 max_classifier_instruction_tokens = 256
+reuse_parent_compaction = false
 max_parent_compaction_tokens = 384
 
 [guardianv2.review_scope]
@@ -187,6 +188,7 @@ max_recent_non_user_entries = 12
             reasoning_effort: Some(codex_protocol::openai_models::ReasoningEffort::Minimal),
             max_action_tokens: Some(512),
             max_classifier_instruction_tokens: Some(256),
+            reuse_parent_compaction: Some(false),
             max_parent_compaction_tokens: Some(384),
             review_scope: Some(crate::GuardianV2ReviewScopeConfigToml {
                 sandboxed_exec_commands: Some(true),