errors: add toError utility and migrate assertError usages

Add a `toError` utility function to `@backstage/errors` that converts
unknown values to `ErrorLike` objects. If the value is already error-like
it is returned as-is. Strings are used directly as the error message, and
other values are stringified with a fallback to JSON.stringify to avoid
unhelpful `[object Object]` messages.

Non-error causes passed to `CustomErrorBase` are now converted and stored
using `toError` rather than discarded. Existing `assertError` call sites
across the codebase are migrated to `toError`.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

packages/cli/src/wiring/lazy.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { assertError } from '@backstage/errors';
+import { toError } from '@backstage/errors';
 import { exitWithError } from './errors';
 
 type ActionFunc = (...args: any[]) => Promise<void>;
@@ -40,8 +40,7 @@ export function lazy<TModule extends object>(
 
       process.exit(0);
     } catch (error) {
-      assertError(error);
-      exitWithError(error);
+      exitWithError(toError(error));
     }
   };
 }