Keep session defaults static during config batch writes (#34940)

## What changed

- Treat batch writes containing only `model`, `model_reasoning_effort`,
  `plan_mode_reasoning_effort`, `service_tier`, or `personality` as defaults for
  future sessions, even when `reloadUserConfig` is requested.
- Keep runtime config reloads and skill/plugin cache invalidation for other
  config changes, and document which settings remain session-static.
- Preserve cached skill listings after session-default writes until a forced
  reload, with test coverage for each supported default.

GitOrigin-RevId: 6d988014cf4758ceb9422a11f7c2bd5fc6b9f90a

codex-rs/app-server-protocol/schema/json/ClientRequest.json

@@ -528,7 +528,7 @@
           ]
         },
         "reloadUserConfig": {
-          "description": "When true, hot-reload the updated user config into all loaded threads after writing.",
+          "description": "When true, hot-reload updated runtime settings into loaded threads after writing. Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and personality defaults are not reloaded.",
           "type": "boolean"
         }
       },

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.schemas.json

@@ -8241,7 +8241,7 @@
             ]
           },
           "reloadUserConfig": {
-            "description": "When true, hot-reload the updated user config into all loaded threads after writing.",
+            "description": "When true, hot-reload updated runtime settings into loaded threads after writing. Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and personality defaults are not reloaded.",
             "type": "boolean"
           }
         },

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -4419,7 +4419,7 @@
           ]
         },
         "reloadUserConfig": {
-          "description": "When true, hot-reload the updated user config into all loaded threads after writing.",
+          "description": "When true, hot-reload updated runtime settings into loaded threads after writing. Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and personality defaults are not reloaded.",
           "type": "boolean"
         }
       },

codex-rs/app-server-protocol/schema/json/v2/ConfigBatchWriteParams.json

@@ -47,7 +47,7 @@
       ]
     },
     "reloadUserConfig": {
-      "description": "When true, hot-reload the updated user config into all loaded threads after writing.",
+      "description": "When true, hot-reload updated runtime settings into loaded threads after writing. Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and personality defaults are not reloaded.",
       "type": "boolean"
     }
   },

codex-rs/app-server-protocol/schema/typescript/v2/ConfigBatchWriteParams.ts

@@ -9,6 +9,8 @@ export type ConfigBatchWriteParams = { edits: Array<ConfigEdit>,
  */
 filePath?: string | null, expectedVersion?: string | null,
 /**
- * When true, hot-reload the updated user config into all loaded threads after writing.
+ * When true, hot-reload updated runtime settings into loaded threads after writing.
+ * Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and
+ * personality defaults are not reloaded.
  */
 reloadUserConfig?: boolean, };

codex-rs/app-server-protocol/src/protocol/v2/config.rs

@@ -864,7 +864,9 @@ pub struct ConfigBatchWriteParams {
     pub file_path: Option<String>,
     #[ts(optional = nullable)]
     pub expected_version: Option<String>,
-    /// When true, hot-reload the updated user config into all loaded threads after writing.
+    /// When true, hot-reload updated runtime settings into loaded threads after writing.
+    /// Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and
+    /// personality defaults are not reloaded.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub reload_user_config: bool,
 }

codex-rs/app-server/README.md

@@ -247,7 +247,7 @@ Example with notification opt-out:
 - `externalAgentConfig/import` — apply selected external-agent migration items by passing explicit `migrationItems` with `cwd` (`null` for home) and any `details` returned by detect. Pass the same optional `migrationSource` used for detection so the server reads from the matching source; omitted, `null`, or unrecognized values retain the default behavior. The optional `source` identifies the product that initiated the import, while the optional opaque `providerId` attributes analytics to the provider selected by that product without affecting migration-source selection. The response acknowledges the synchronous import phase with an `importId`. Expected migration failures are reported as per-item failures rather than JSON-RPC errors, so the server still returns that `importId` and emits `externalAgentConfig/import/completed` with the same ID once all synchronous and background work finishes. The completion notification contains type-level `itemTypeResults` with successes and failures, including raw failure messages for the client to report separately.
 - `externalAgentConfig/import/readHistories` — read completed import histories and connector candidates detected from successfully imported session histories. Connector candidates include a normalized display `name`, the number of imported sessions that used the connector, and the source metadata field used for detection.
 - `config/value/write` — write a single config key/value to the user's config.toml on disk; dotted paths such as `desktop.someKey` use the same generic write surface. Writes that overlap a managed requirement are rejected with `configRequirementReadonly`.
-- `config/batchWrite` — apply multiple config edits atomically to the user's config.toml on disk, with optional `reloadUserConfig: true` to hot-reload loaded threads, including multiple `desktop.*` edits.
+- `config/batchWrite` — apply multiple config edits atomically to the user's config.toml on disk, with optional `reloadUserConfig: true` to hot-reload loaded threads, including multiple `desktop.*` edits. Session-static model, reasoning-effort, Plan-mode reasoning-effort, service-tier, and personality defaults do not reload existing threads.
 - `configRequirements/read` — fetch loaded requirements constraints from `requirements.toml` and/or MDM (or `null` if none are configured), including exact managed values (`sqliteHome`, `logDir`, `modelCatalogJson`, `checkForUpdateOnStartup`, `allowLoginShell`, `feedback.enabled`, and `windowsSandboxPrivateDesktop`), allow-lists (`allowedApprovalPolicies`, `allowedSandboxModes`, `allowedWebSearchModes`), the layered permission-profile allow map (`allowedPermissionProfiles`), the managed permission-profile default (`defaultPermissions`), lifecycle hook lockdown (`allowManagedHooksOnly`), remote-control policy (`allowRemoteControl`; `false` force-disables remote control while `true` or `null` preserves existing behavior), computer use policy (`computerUse`), pinned feature values (`featureRequirements`), managed lifecycle hooks (`hooks`, including each command handler's optional `additionalContextLimit`), `enforceResidency`, managed new-thread defaults (`models.newThread.model`, `models.newThread.modelReasoningEffort`, and `models.newThread.serviceTier`), and `network` constraints such as canonical domain/socket permissions plus `managedAllowedDomainsOnly` and `dangerFullAccessDenylistOnly`.
 
 ### Example: Start or resume a thread

codex-rs/app-server/src/request_processors/config_processor.rs

@@ -136,9 +136,26 @@ impl ConfigRequestProcessor {
         &self,
         params: ConfigBatchWriteParams,
     ) -> Result<ClientResponsePayload, JSONRPCErrorError> {
-        self.handle_config_mutation_result(self.batch_write_inner(params).await)
-            .await
-            .map(ClientResponsePayload::ConfigBatchWrite)
+        let session_defaults_only = !params.edits.is_empty()
+            && params.edits.iter().all(|edit| {
+                matches!(
+                    edit.key_path.as_str(),
+                    "model"
+                        | "model_reasoning_effort"
+                        | "plan_mode_reasoning_effort"
+                        | "service_tier"
+                        | "personality"
+                )
+            });
+        let reload_user_config = params.reload_user_config;
+        let response = self.batch_write_inner(params).await?;
+        if !session_defaults_only {
+            self.handle_config_mutation().await;
+            if reload_user_config {
+                self.reload_user_config().await;
+            }
+        }
+        Ok(ClientResponsePayload::ConfigBatchWrite(response))
     }
 
     pub(crate) async fn experimental_feature_enablement_set(
@@ -149,6 +166,9 @@ impl ConfigRequestProcessor {
         let response = self
             .handle_config_mutation_result(self.set_experimental_feature_enablement(params).await)
             .await?;
+        if !response.enablement.is_empty() {
+            self.reload_user_config().await;
+        }
         self.outgoing
             .send_response_as(
                 request_id,
@@ -219,7 +239,6 @@ impl ConfigRequestProcessor {
         &self,
         params: ConfigBatchWriteParams,
     ) -> Result<ConfigWriteResponse, JSONRPCErrorError> {
-        let reload_user_config = params.reload_user_config;
         let pending_changes = codex_core_plugins::toggles::collect_plugin_enabled_candidates(
             params
                 .edits
@@ -232,9 +251,6 @@ impl ConfigRequestProcessor {
             .await
             .map_err(map_error)?;
         self.emit_plugin_toggle_events(pending_changes).await;
-        if reload_user_config {
-            self.reload_user_config().await;
-        }
         Ok(response)
     }
 
@@ -270,7 +286,6 @@ impl ConfigRequestProcessor {
             .map_err(|_| internal_error("failed to update feature enablement"))?;
 
         self.load_latest_config(/*fallback_cwd*/ None).await?;
-        self.reload_user_config().await;
 
         Ok(ExperimentalFeatureEnablementSetResponse { enablement })
     }

codex-rs/app-server/tests/suite/v2/skills_list.rs

@@ -7,8 +7,12 @@ use app_test_support::MockResponsesConfig;
 use app_test_support::TestAppServer;
 use app_test_support::create_mock_responses_server_repeating_assistant;
 use app_test_support::write_chatgpt_auth;
+use codex_app_server_protocol::ConfigBatchWriteParams;
+use codex_app_server_protocol::ConfigEdit;
+use codex_app_server_protocol::ConfigWriteResponse;
 use codex_app_server_protocol::ExperimentalFeatureEnablementSetParams;
 use codex_app_server_protocol::ExperimentalFeatureEnablementSetResponse;
+use codex_app_server_protocol::MergeStrategy;
 use codex_app_server_protocol::PluginListParams;
 use codex_app_server_protocol::PluginListResponse;
 use codex_app_server_protocol::SkillsChangedNotification;
@@ -587,7 +591,8 @@ async fn skills_list_preserves_requested_cwd_order() -> Result<()> {
 }
 
 #[tokio::test]
-async fn skills_list_uses_cached_result_until_force_reload() -> Result<()> {
+async fn skills_list_uses_cached_result_after_session_default_writes_until_force_reload()
+-> Result<()> {
     let codex_home = TempDir::new()?;
     let cwd = TempDir::new()?;
 
@@ -621,6 +626,47 @@ async fn skills_list_uses_cached_result_until_force_reload() -> Result<()> {
         "---\nname: late-extra-skill\ndescription: late skill\n---\n\n# Body\n",
     )?;
 
+    for edits in [
+        vec![ConfigEdit {
+            key_path: "plan_mode_reasoning_effort".to_string(),
+            value: serde_json::json!("high"),
+            merge_strategy: MergeStrategy::Replace,
+        }],
+        vec![ConfigEdit {
+            key_path: "service_tier".to_string(),
+            value: serde_json::json!("fast"),
+            merge_strategy: MergeStrategy::Replace,
+        }],
+        vec![ConfigEdit {
+            key_path: "personality".to_string(),
+            value: serde_json::json!("friendly"),
+            merge_strategy: MergeStrategy::Replace,
+        }],
+        vec![
+            ConfigEdit {
+                key_path: "model".to_string(),
+                value: serde_json::json!("gpt-5.4"),
+                merge_strategy: MergeStrategy::Replace,
+            },
+            ConfigEdit {
+                key_path: "model_reasoning_effort".to_string(),
+                value: serde_json::json!("high"),
+                merge_strategy: MergeStrategy::Replace,
+            },
+        ],
+    ] {
+        let write_id = mcp
+            .send_config_batch_write_request(ConfigBatchWriteParams {
+                edits,
+                file_path: None,
+                expected_version: None,
+                reload_user_config: true,
+            })
+            .await?;
+        let _: ConfigWriteResponse =
+            timeout(DEFAULT_TIMEOUT, mcp.read_response(write_id)).await??;
+    }
+
     let second_request_id = mcp
         .send_skills_list_request(SkillsListParams {
             cwds: vec![cwd.path().to_path_buf()],

codex-rs/core/src/session/mod.rs

@@ -1626,8 +1626,6 @@ impl Session {
             (previous_config, new_config, config)
         };
         self.emit_config_changed_contributors(previous_config.as_ref(), new_config.as_ref());
-        self.services.skills_service.clear_cache();
-        self.services.plugins_manager.clear_cache();
         let environments = self.services.turn_environments.snapshot().await;
         let hooks = build_hooks_for_config(
             config.as_ref(),
@@ -1791,6 +1789,8 @@ impl Session {
                 resolve_tool_suggest_config_from_layer_stack(&config.config_layer_stack);
             config
         };
+        self.services.skills_service.clear_cache();
+        self.services.plugins_manager.clear_cache();
         self.refresh_runtime_config(next_config).await;
     }