Preserve null developer instructions (#16976)

Preserve explicit null developer-instruction overrides across app-server
resume and fork flows.

codex-rs/rollout/src/metadata_tests.rs

@@ -56,6 +56,7 @@ async fn extract_metadata_from_rollout_uses_session_meta() {
         agent_role: None,
         model_provider: Some("openai".to_string()),
         base_instructions: None,
+        developer_instructions: None,
         dynamic_tools: None,
         memory_mode: None,
     };
@@ -107,6 +108,7 @@ async fn extract_metadata_from_rollout_returns_latest_memory_mode() {
         agent_role: None,
         model_provider: Some("openai".to_string()),
         base_instructions: None,
+        developer_instructions: None,
         dynamic_tools: None,
         memory_mode: None,
     };
@@ -369,6 +371,7 @@ fn write_rollout_in_sessions_with_cwd(
         agent_role: None,
         model_provider: Some("test-provider".to_string()),
         base_instructions: None,
+        developer_instructions: None,
         dynamic_tools: None,
         memory_mode: None,
     };

codex-rs/rollout/src/recorder.rs

@@ -82,6 +82,7 @@ pub enum RolloutRecorderParams {
         forked_from_id: Option<ThreadId>,
         source: SessionSource,
         base_instructions: Option<BaseInstructions>,
+        developer_instructions: Option<Option<String>>,
         dynamic_tools: Vec<DynamicToolSpec>,
         event_persistence_mode: EventPersistenceMode,
     },
@@ -111,6 +112,7 @@ impl RolloutRecorderParams {
         forked_from_id: Option<ThreadId>,
         source: SessionSource,
         base_instructions: Option<BaseInstructions>,
+        developer_instructions: Option<Option<String>>,
         dynamic_tools: Vec<DynamicToolSpec>,
         event_persistence_mode: EventPersistenceMode,
     ) -> Self {
@@ -119,6 +121,7 @@ impl RolloutRecorderParams {
             forked_from_id,
             source,
             base_instructions,
+            developer_instructions,
             dynamic_tools,
             event_persistence_mode,
         }
@@ -380,6 +383,7 @@ impl RolloutRecorder {
                     forked_from_id,
                     source,
                     base_instructions,
+                    developer_instructions,
                     dynamic_tools,
                     event_persistence_mode,
                 } => {
@@ -409,6 +413,7 @@ impl RolloutRecorder {
                         source,
                         model_provider: Some(config.model_provider_id().to_string()),
                         base_instructions: Some(base_instructions),
+                        developer_instructions,
                         dynamic_tools: if dynamic_tools.is_empty() {
                             None
                         } else {

codex-rs/rollout/src/recorder_tests.rs

@@ -74,6 +74,7 @@ async fn recorder_materializes_only_after_explicit_persist() -> std::io::Result<
             /*forked_from_id*/ None,
             SessionSource::Exec,
             Some(BaseInstructions::default()),
+            /*developer_instructions*/ None,
             Vec::new(),
             EventPersistenceMode::Limited,
         ),
@@ -167,6 +168,7 @@ async fn metadata_irrelevant_events_touch_state_db_updated_at() -> std::io::Resu
             /*forked_from_id*/ None,
             SessionSource::Cli,
             Some(BaseInstructions::default()),
+            /*developer_instructions*/ None,
             Vec::new(),
             EventPersistenceMode::Limited,
         ),

codex-rs/rollout/src/tests.rs

@@ -1140,6 +1140,7 @@ async fn test_updated_at_uses_file_mtime() -> Result<()> {
                 agent_role: None,
                 model_provider: Some("test-provider".into()),
                 base_instructions: None,
+                developer_instructions: None,
                 dynamic_tools: None,
                 memory_mode: None,
             },