Preserve plugin install failure subtypes during imports (#33182)

## What changed

- Add `subErrorType` to external agent config import failures and carry it through progress and completion notifications, persisted import histories, and analytics.
- Expose plugin store failure subtypes from `PluginInstallError` so manual installs and imported plugins report details such as `failed_to_copy_plugin_file` while failures without a subtype remain `null`.
- Keep existing persisted import records compatible by defaulting the new field when it is absent.

## Testing

- Cover store I/O subtype extraction, analytics serialization, persisted import histories, and migration notification fixtures.

GitOrigin-RevId: ec1a85623fc826cbd7cfe9f55c2dd2bc86665937

codex-rs/core-plugins/src/manager.rs

@@ -1312,7 +1312,7 @@ impl PluginsManager {
                 self.track_plugin_install_failed(
                     &plugin_id,
                     plugin_install_error_type(&err),
-                    plugin_install_sub_error_type(&err),
+                    err.sub_error_type(),
                     err.to_string(),
                 );
                 Err(err)
@@ -1375,7 +1375,7 @@ impl PluginsManager {
             self.track_plugin_install_failed(
                 &resolved.plugin_id,
                 plugin_install_error_type(&err),
-                plugin_install_sub_error_type(&err),
+                err.sub_error_type(),
                 err.to_string(),
             );
             return Err(err);
@@ -1387,7 +1387,7 @@ impl PluginsManager {
                 self.track_plugin_install_failed(
                     &plugin_id,
                     plugin_install_error_type(&err),
-                    plugin_install_sub_error_type(&err),
+                    err.sub_error_type(),
                     err.to_string(),
                 );
                 Err(err)
@@ -1450,6 +1450,7 @@ impl PluginsManager {
                 self.telemetry_metadata_for_plugin_id(plugin_id),
                 self.plugin_install_source,
                 error_type.to_string(),
+                sub_error_type,
             );
         }
     }
@@ -2728,6 +2729,13 @@ impl PluginInstallError {
             ) | Self::Store(PluginStoreError::Invalid(_))
         )
     }
+
+    pub fn sub_error_type(&self) -> Option<String> {
+        match self {
+            Self::Store(err) => err.sub_error_type(),
+            Self::Marketplace(_) | Self::Remote(_) | Self::Config(_) | Self::Join(_) => None,
+        }
+    }
 }
 
 fn plugin_install_error_type(err: &PluginInstallError) -> &'static str {
@@ -2740,16 +2748,6 @@ fn plugin_install_error_type(err: &PluginInstallError) -> &'static str {
     }
 }
 
-fn plugin_install_sub_error_type(err: &PluginInstallError) -> Option<String> {
-    match err {
-        PluginInstallError::Store(err) => err.sub_error_type(),
-        PluginInstallError::Marketplace(_)
-        | PluginInstallError::Remote(_)
-        | PluginInstallError::Config(_)
-        | PluginInstallError::Join(_) => None,
-    }
-}
-
 fn marketplace_error_type(err: &MarketplaceError) -> &'static str {
     match err {
         MarketplaceError::Io { .. } => "marketplace_io",