refactor(oauth): add provider registry

packages/coding-agent/src/core/extensions/loader.ts

@@ -32,6 +32,7 @@ import type {
 	ExtensionRuntime,
 	LoadExtensionsResult,
 	MessageRenderer,
+	ProviderConfig,
 	RegisteredCommand,
 	ToolDefinition,
 } from "./types.js";
@@ -122,6 +123,7 @@ export function createExtensionRuntime(): ExtensionRuntime {
 		getThinkingLevel: notInitialized,
 		setThinkingLevel: notInitialized,
 		flagValues: new Map(),
+		pendingProviderRegistrations: [],
 	};
 }
 
@@ -238,6 +240,10 @@ function createExtensionAPI(
 			runtime.setThinkingLevel(level);
 		},
 
+		registerProvider(name: string, config: ProviderConfig) {
+			runtime.pendingProviderRegistrations.push({ name, config });
+		},
+
 		events: eventBus,
 	} as ExtensionAPI;