fix(coding-agent): surface auth storage save failures

closes #6223

packages/coding-agent/src/core/auth-storage.ts

@@ -271,12 +271,21 @@ export class AuthStorage {
 		}
 	}
 
-	private persistProviderChange(provider: string, credential: AuthCredential | undefined): void {
+	private persistProviderChange(provider: string, credential: AuthCredential | undefined): AuthStorageData {
 		if (this.loadError) {
-			return;
+			this.reload();
+		}
+
+		if (this.loadError) {
+			const error = new Error(
+				`Cannot update auth storage because it could not be loaded: ${this.loadError.message}`,
+			);
+			this.recordError(error);
+			throw error;
 		}
 
 		try {
+			let persistedData: AuthStorageData = {};
 			this.storage.withLock((current) => {
 				const currentData = this.parseStorageData(current);
 				const merged: AuthStorageData = { ...currentData };
@@ -285,10 +294,14 @@ export class AuthStorage {
 				} else {
 					delete merged[provider];
 				}
+				persistedData = merged;
 				return { result: undefined, next: JSON.stringify(merged, null, 2) };
 			});
+			this.loadError = null;
+			return persistedData;
 		} catch (error) {
 			this.recordError(error);
+			throw error;
 		}
 	}
 
@@ -311,16 +324,14 @@ export class AuthStorage {
 	 * Set credential for a provider.
 	 */
 	set(provider: string, credential: AuthCredential): void {
-		this.data[provider] = credential;
-		this.persistProviderChange(provider, credential);
+		this.data = this.persistProviderChange(provider, credential);
 	}
 
 	/**
 	 * Remove credential for a provider.
 	 */
 	remove(provider: string): void {
-		delete this.data[provider];
-		this.persistProviderChange(provider, undefined);
+		this.data = this.persistProviderChange(provider, undefined);
 	}
 
 	/**