enable/disable remote control at runtime, not via features (#22578)

## Why
reapplies https://github.com/openai/codex/pull/22386 which was
previously reverted

Also, introduce `remoteControl/enable` and `remoteControl/disable`
app-server APIs to toggle on/off remote control at runtime for a given
running app-server instance.

## What Changed

- Adds experimental v2 RPCs:
  - `remoteControl/enable`
  - `remoteControl/disable`
- Adds `RemoteControlRequestProcessor` and routes the new RPCs through
it instead of `ConfigRequestProcessor`.
- Adds named `RemoteControlHandle::enable`, `disable`, and `status`
methods.
- Makes `remoteControl/enable` return an error when sqlite state DB is
unavailable, while keeping enrollment/websocket failures as async status
updates.
- Adds `AppServerRuntimeOptions.remote_control_enabled` and hidden
`--remote-control` flags for `codex app-server` and `codex-app-server`.
- Updates managed daemon startup to use `codex app-server
--remote-control --listen unix://`.
- Marks `Feature::RemoteControl` as removed and ignores
`[features].remote_control`.
- Updates app-server README entries for the new remote-control methods.

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

@@ -6,7 +6,6 @@ use crate::error_code::internal_error;
 use crate::error_code::invalid_request;
 use crate::outgoing_message::ConnectionRequestId;
 use crate::outgoing_message::OutgoingMessageSender;
-use crate::transport::RemoteControlHandle;
 use codex_analytics::AnalyticsEventsClient;
 use codex_app_server_protocol::AppListUpdatedNotification;
 use codex_app_server_protocol::ClientResponsePayload;
@@ -39,7 +38,6 @@ use codex_config::MatcherGroup as CoreMatcherGroup;
 use codex_config::ResidencyRequirement as CoreResidencyRequirement;
 use codex_config::SandboxModeRequirement as CoreSandboxModeRequirement;
 use codex_core::ThreadManager;
-use codex_features::Feature;
 use codex_features::canonical_feature_for_key;
 use codex_features::feature_for_key;
 use codex_login::AuthManager;
@@ -67,7 +65,6 @@ pub(crate) struct ConfigRequestProcessor {
     auth_manager: Arc<AuthManager>,
     thread_manager: Arc<ThreadManager>,
     analytics_events_client: AnalyticsEventsClient,
-    remote_control_handle: Option<RemoteControlHandle>,
 }
 
 impl ConfigRequestProcessor {
@@ -77,7 +74,6 @@ impl ConfigRequestProcessor {
         auth_manager: Arc<AuthManager>,
         thread_manager: Arc<ThreadManager>,
         analytics_events_client: AnalyticsEventsClient,
-        remote_control_handle: Option<RemoteControlHandle>,
     ) -> Self {
         Self {
             outgoing,
@@ -85,7 +81,6 @@ impl ConfigRequestProcessor {
             auth_manager,
             thread_manager,
             analytics_events_client,
-            remote_control_handle,
         }
     }
 
@@ -187,21 +182,6 @@ impl ConfigRequestProcessor {
     pub(crate) async fn handle_config_mutation(&self) {
         self.thread_manager.plugins_manager().clear_cache();
         self.thread_manager.skills_manager().clear_cache();
-        let Some(remote_control_handle) = &self.remote_control_handle else {
-            return;
-        };
-
-        match self.load_latest_config(/*fallback_cwd*/ None).await {
-            Ok(config) => {
-                remote_control_handle.set_enabled(config.features.enabled(Feature::RemoteControl));
-            }
-            Err(error) => {
-                tracing::warn!(
-                    "failed to load config for remote control enablement refresh after config mutation: {}",
-                    error.message
-                );
-            }
-        }
     }
 
     async fn handle_config_mutation_result<T>(

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

@@ -0,0 +1,43 @@
+use crate::error_code::internal_error;
+use crate::error_code::invalid_request;
+use crate::transport::RemoteControlHandle;
+use crate::transport::RemoteControlUnavailable;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_app_server_protocol::RemoteControlDisableResponse;
+use codex_app_server_protocol::RemoteControlEnableResponse;
+
+#[derive(Clone)]
+pub(crate) struct RemoteControlRequestProcessor {
+    remote_control_handle: Option<RemoteControlHandle>,
+}
+
+impl RemoteControlRequestProcessor {
+    pub(crate) fn new(remote_control_handle: Option<RemoteControlHandle>) -> Self {
+        Self {
+            remote_control_handle,
+        }
+    }
+
+    pub(crate) fn enable(&self) -> Result<RemoteControlEnableResponse, JSONRPCErrorError> {
+        let handle = self.handle()?;
+        handle
+            .enable()
+            .map(RemoteControlEnableResponse::from)
+            .map_err(map_unavailable)
+    }
+
+    pub(crate) fn disable(&self) -> Result<RemoteControlDisableResponse, JSONRPCErrorError> {
+        let handle = self.handle()?;
+        Ok(RemoteControlDisableResponse::from(handle.disable()))
+    }
+
+    fn handle(&self) -> Result<&RemoteControlHandle, JSONRPCErrorError> {
+        self.remote_control_handle
+            .as_ref()
+            .ok_or_else(|| internal_error("remote control is unavailable for this app-server"))
+    }
+}
+
+fn map_unavailable(err: RemoteControlUnavailable) -> JSONRPCErrorError {
+    invalid_request(err.to_string())
+}