[FEATURE] Pre-install Dart/Flutter SDK in Claude Code Web cloud environment

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The Claude Code Web cloud environment comes with many language runtimes pre-installed (Node.js, Python, Go, Ruby, Bun, Rust, Java/Maven/Gradle, PHP), but Dart and Flutter SDK are not included.

For Flutter/Dart projects, the SessionStart hook must git clone the entire Flutter SDK (~1.4 GB) on every fresh session, which adds significant startup latency. While the SDK is cached on session resume, cold starts are noticeably slow.

Proposed Solution

Pre-install the Dart SDK (or ideally the Flutter SDK) in the cloud environment's base image, similar to how Go, Ruby, and other runtimes are already included.

Even just the Dart SDK (~50 MB compressed) would allow dart analyze, dart pub get, and dart test to work out of the box without any SessionStart hook setup.

Alternative Solutions

Currently using a SessionStart hook that runs git clone --depth 1 of the Flutter SDK on cold start. The SDK is cached across session resumes, but every fresh session incurs the full ~1.4 GB download (Dart SDK alone is 611 MB).

Another option considered was installing only the standalone Dart SDK (~50 MB) instead of the full Flutter SDK, but flutter pub get is needed for Flutter projects with platform-specific plugin dependencies.

Related: #16849 (Dart/Flutter LSP support)

Priority

Low - Nice to have

Feature Category

Performance and speed

Use Case Example

1. Open a Flutter game project on Claude Code Web (claude.ai/code)
2. Session starts → SessionStart hook runs git clone of Flutter SDK (~1.4 GB)
3. Wait for download, Dart SDK extraction (611 MB), and flutter pub get
4. Finally able to start working (e.g. dart analyze, editing code, running tests)

With Dart/Flutter pre-installed, step 2-3 would be eliminated entirely, and the session would be ready to use immediately — just like Node.js or Python projects are today.

Additional Context

_No response_