
- When `--web-renderer` is omitted, keep the value `null` until it later materializes to either `canvaskit` or `skwasm`. - No more hardcoded defaults anywhere. We use `WebRendererMode.defaultForJs/defaultForWasm` instead. - When in `--wasm` mode, the JS fallback is now `canvaskit` instead of `auto`. - Add test for defaulting to `skwasm` when `--wasm` is enabled. Fixes https://github.com/flutter/flutter/issues/149826