[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-protocol/src/protocol/v2/config.rs

@@ -677,6 +677,7 @@ pub struct ExternalAgentConfigImportResponse {
 #[ts(export_to = "v2/")]
 pub struct ExternalAgentConfigImportItemTypeFailure {
     pub item_type: ExternalAgentConfigMigrationItemType,
+    pub error_type: Option<String>,
     pub failure_stage: String,
     pub message: String,
     pub cwd: Option<PathBuf>,
@@ -702,6 +703,31 @@ pub struct ExternalAgentConfigImportTypeResult {
     pub failures: Vec<ExternalAgentConfigImportItemTypeFailure>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ExternalAgentConfigImportHistory {
+    pub import_id: String,
+    pub completed_at_ms: i64,
+    pub successes: Vec<ExternalAgentConfigImportItemTypeSuccess>,
+    pub failures: Vec<ExternalAgentConfigImportItemTypeFailure>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ExternalAgentConfigImportHistoriesReadResponse {
+    pub data: Vec<ExternalAgentConfigImportHistory>,
+}
+
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct ExternalAgentConfigImportProgressNotification {
+    pub import_id: String,
+    pub item_type_results: Vec<ExternalAgentConfigImportTypeResult>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]