Improve error message for routing

[mosuem]

Making it a bit less cryptic.

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.

[github-actions]

PR Health

License Headers ✔️

// Copyright (c) 2026, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

Files
no missing headers

All source files should start with a license header.

Unrelated files missing license headers

Files
pkgs/hooks_runner/test_data/download_assets/hook/build.dart
pkgs/jni/test/debug_release_test.dart
pkgs/objective_c/example/command_line/lib/main.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

This check can be disabled by tagging the PR with skip-license-check.

API leaks ✔️

The following packages contain symbols visible in the public API, but not exported by the library. Export these symbols or remove them from your publicly visible API.

Package	Leaked API symbol	Leaking sources

This check can be disabled by tagging the PR with skip-leaking-check.

Breaking changes ✔️

Package	Change	Current Version	New Version	Needed Version	Looking good?
code_assets	None	1.0.0	1.0.0	1.0.0	✔️
data_assets	None	0.19.6	0.19.6	0.19.6	✔️
hooks	None	1.0.1	1.0.1	1.0.1	✔️

This check can be disabled by tagging the PR with skip-breaking-check.

Changelog Entry ❗

Package	Changed Files
package:code_assets	pkgs/code_assets/lib/src/code_assets/validation.dart
package:data_assets	pkgs/data_assets/lib/src/data_assets/validation.dart
package:hooks	pkgs/hooks/lib/src/validation.dart

Changes to files need to be accounted for in their respective changelogs.

This check can be disabled by tagging the PR with skip-changelog-check.

[dcharkes]

Bump package hooks to 0.19.1-wip.

[goderbauer]

@mosuem to sync to Head.