Migrate from Event to Message API for Bevy 0.17

[not-elm]

Summary

This PR migrates the codebase from the deprecated Event API to the new Message API introduced in Bevy 0.17.

Changes

New Modules

• src/action/once/message.rs: New module with message-based actions

  • write<M>() - Write a message (replaces send())
  • write_default<M>() - Write default message (replaces send_default())
  • app_exit_success() - Exit app successfully

• src/action/wait/message.rs: New module for waiting on messages

  • comes<M>() - Wait until message arrives
  • comes_and<M>(predicate) - Wait for message matching predicate
  • read<M>() - Wait and return message
  • read_and<M>(predicate) - Wait and return matching message

Deprecated Modules

• src/action/once/event.rs: All functions marked as #[deprecated] with migration guidance

  • Functions now delegate to once::message equivalents

• src/action/wait/event.rs: All functions marked as #[deprecated] with migration guidance

  • Functions now delegate to wait::message equivalents

Updated Files

• Examples (5 files): All examples now use message API
• Documentation (11+ files): Updated all docs to use message API
• README.md: Updated example code
• Tests & Inline Docs (18 files): All test code and doc comments updated

Migration Path

The old event modules remain functional but deprecated, allowing gradual migration:

// Old (deprecated)
once::event::send().with(AppExit::Success)
wait::event::read::<MyEvent>()

// New
once::message::write().with(AppExit::Success)
wait::message::read::<MyMessage>()

Test Results

• ✅ All 70 tests passing
• ✅ Zero deprecation warnings in codebase
• ✅ All examples build successfully

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]