[codex] Record external agent import results (#28396)

## Summary
- restore `externalAgentConfig/import/progress` notifications while
keeping `externalAgentConfig/import/completed` as the must-deliver event
- persist completed external-agent config imports in state DB by
`importId`, including concrete success/failure details for config,
AGENTS.md, skills, plugins, MCP servers, subagents, hooks, commands, and
sessions
- add `externalAgentConfig/import/readHistories` so clients can recover
persisted import results after missing the live completion notification
- include `errorType` on import failures in protocol
responses/notifications and persisted DB JSON so future code can
classify failures without another wire/storage shape change

## Validation
- `git diff --check`
- `just test -p codex-state external_agent_config_imports`
- `just test -p codex-app-server-protocol`
- `CODEX_SQLITE_HOME=/private/tmp/codex-app-server-sqlite-read-details
just test -p codex-app-server
external_agent_config_import_sends_completion_notification_for_sync_only_import`

Also ran earlier broader checks before publishing:
- `just test -p codex-state`
-
`CODEX_SQLITE_HOME=/private/tmp/codex-app-server-external-agent-test-sqlite
just test -p codex-app-server external_agent_config`
- `just test -p codex-external-agent-migration`

codex-rs/app-server/src/message_processor.rs

@@ -24,6 +24,7 @@ use crate::request_processors::CommandExecRequestProcessor;
 use crate::request_processors::ConfigRequestProcessor;
 use crate::request_processors::EnvironmentRequestProcessor;
 use crate::request_processors::ExternalAgentConfigRequestProcessor;
+use crate::request_processors::ExternalAgentConfigRequestProcessorArgs;
 use crate::request_processors::FeedbackRequestProcessor;
 use crate::request_processors::FsRequestProcessor;
 use crate::request_processors::GitRequestProcessor;
@@ -475,7 +476,7 @@ impl MessageProcessor {
             thread_watch_manager.clone(),
             Arc::clone(&thread_list_state_permit),
             thread_goal_processor.clone(),
-            state_db,
+            state_db.clone(),
             log_db,
             Arc::clone(&skills_watcher),
         );
@@ -511,15 +512,17 @@ impl MessageProcessor {
             thread_manager.clone(),
             analytics_events_client,
         );
-        let external_agent_config_processor = ExternalAgentConfigRequestProcessor::new(
-            outgoing.clone(),
-            Arc::clone(&thread_manager),
-            Arc::clone(&thread_store),
-            config_manager.clone(),
-            config_processor.clone(),
-            arg0_paths,
-            config.codex_home.to_path_buf(),
-        );
+        let external_agent_config_processor =
+            ExternalAgentConfigRequestProcessor::new(ExternalAgentConfigRequestProcessorArgs {
+                outgoing: outgoing.clone(),
+                thread_manager: Arc::clone(&thread_manager),
+                thread_store: Arc::clone(&thread_store),
+                config_manager: config_manager.clone(),
+                config_processor: config_processor.clone(),
+                state_db,
+                arg0_paths,
+                codex_home: config.codex_home.to_path_buf(),
+            });
         let environment_processor =
             EnvironmentRequestProcessor::new(thread_manager.environment_manager());
         let fs_processor = FsRequestProcessor::new(
@@ -947,6 +950,11 @@ impl MessageProcessor {
                 .import(request_id.clone(), params)
                 .await
                 .map(|()| None),
+            ClientRequest::ExternalAgentConfigImportHistoriesRead { .. } => self
+                .external_agent_config_processor
+                .read_import_histories()
+                .await
+                .map(|response| Some(response.into())),
             ClientRequest::ConfigValueWrite { params, .. } => {
                 self.config_processor.value_write(params).await.map(Some)
             }