fix(auth): restore BetterAuth OIDC flow across api/web/compose

apps/api/src/auth/auth.controller.ts

@@ -133,6 +133,11 @@ export class AuthController {
       );
 
       if (!res.headersSent) {
+        const mappedError = this.mapToHttpException(error);
+        if (mappedError) {
+          throw mappedError;
+        }
+
         throw new HttpException(
           "Unable to complete authentication. Please try again in a moment.",
           HttpStatus.INTERNAL_SERVER_ERROR
@@ -159,4 +164,45 @@ export class AuthController {
     // Fall back to direct IP
     return req.ip ?? req.socket.remoteAddress ?? "unknown";
   }
+
+  /**
+   * Preserve known HTTP errors from BetterAuth/better-call instead of converting
+   * every failure into a generic 500.
+   */
+  private mapToHttpException(error: unknown): HttpException | null {
+    if (error instanceof HttpException) {
+      return error;
+    }
+
+    if (!error || typeof error !== "object") {
+      return null;
+    }
+
+    const statusCode = "statusCode" in error ? error.statusCode : undefined;
+    if (!this.isHttpStatus(statusCode)) {
+      return null;
+    }
+
+    const responseBody = "body" in error && error.body !== undefined ? error.body : undefined;
+    if (
+      responseBody !== undefined &&
+      responseBody !== null &&
+      (typeof responseBody === "string" || typeof responseBody === "object")
+    ) {
+      return new HttpException(responseBody, statusCode);
+    }
+
+    const message =
+      "message" in error && typeof error.message === "string" && error.message.length > 0
+        ? error.message
+        : "Authentication request failed";
+    return new HttpException(message, statusCode);
+  }
+
+  private isHttpStatus(value: unknown): value is number {
+    if (typeof value !== "number" || !Number.isInteger(value)) {
+      return false;
+    }
+    return value >= 400 && value <= 599;
+  }
 }