What kind of change does this PR introduce?

CI/CD enhancement - Improves the preview release workflow and cross-repository testing integration.

What is the current behavior?

• Preview releases are created but there's no automated way to test compatibility with downstream packages
• No cross-repository testing between realtime-js and supabase-js
• Manual testing required to verify changes don't break integration points
• Limited feedback loop for developers on cross-package compatibility

What is the new behavior?

• Automated Cross-Repo Testing: Preview releases automatically trigger compatibility tests in supabase-js
• Smart Triggering: Only runs on actual source code changes (src/, package files, tsconfig) to avoid unnecessary builds
• Enhanced Control: Manual workflow dispatch with configurable options for target branch and test triggering
• Better UX: PR comments show preview package URLs and test status updates
• Secure Integration: Uses GitHub App authentication for cross-repository workflow triggering

Key Features

🚀 Cross-Repository Test Integration

• Automatically triggers supabase-js external tests when realtime-js changes are made
• Passes preview package URL and metadata to downstream tests
• Supports both PR and push-based workflows

⚡ Optimized Triggering

• Path-based filtering: Only triggers on meaningful changes (src/**, package.json, etc.)
• Label-based control: PRs require trigger: preview label for activation
• Manual override: Workflow dispatch with configurable target branch

💬 Enhanced Feedback

• Automated PR comments with preview package links
• Status updates on cross-repo test progress
• Clear visibility into the testing pipeline

🔒 Secure Cross-Repo Access

• GitHub App-based authentication for repository access
• Scoped permissions to realtime-js and supabase-js repositories only

Testing

This workflow enables:

• Early detection of breaking changes between realtime-js and supabase-js
• Automated compatibility verification for all preview releases
• Faster feedback cycles for developers working on authentication features
• Reduced risk of integration issues in production releases

Additional context

This enhancement creates a robust CI/CD pipeline that ensures realtime-js changes are automatically validated against its primary consumer (supabase-js), significantly improving the development workflow and reducing integration risks.

More context: supabase/supabase-js#1532