size emscripten canvas from iframe

[treeform]

Summary

• Read Emscripten window size from the canvas element (clientWidth/clientHeight) instead of window.innerWidth, so WASM apps inside an iframe use the iframe box.
• Observe canvas resizes and dispatch resize so the framebuffer tracks the iframe when the parent layout changes.

Test plan

• Full-page Emscripten window still fills the browser and UI scale is unchanged.
• Same build inside a small iframe uses the iframe size, not the parent window.
• Resizing the iframe updates the canvas backing store.

Made with Cursor