Hi Doug,
The canvas resolution doesn't affect the loading of raster (pixel-based) images as raster-layers. They will retain their original pixel data when composited with the canvas. The canvas resolution only affects when an SVG vector image is loaded as a raster-layer, as it determines the number of pixels in the resulting raster-layer.
Basically, when you load an image as a raster-layer, it doesn't matter what the canvas resolution is. The canvas resolution only affects the resolution of the canvas as a whole but not the contents of layers that are being composited onto the canvas.
If you load a large high-resolution image it *might* get downscaled a bit just to keep things quick, but not usually in any noticeable way. It's just to avoid unnecessarily expensive compute.
Toolpaths are generated from the canvas composition as a whole, where all of the layers (except paths-layers) are combined per their blending modes, origins, and dimensions, at the canvas' resolution. The contents of a raster-layer are not themselves affected by the canvas resolution. You can think about the canvas as a "camera" that's just capturing the state of the layers within it, and whatever that camera captures is what toolpaths are calculated from - but raster-layers themselves are independent of this camera with their own resolutions.
Text-layers and model-layers are rendered at the canvas resolution, so whenever it changes so do they. The only "permanent" effect that the canvas resolution has is when generating raster-layers from a paths-layer. That occurs at whatever the canvas resolution is at that time and increasing it after the fact will not re-calculate the raster-layers produced using functions like Shapes From Paths, Sweep Paths, Raster/Text Along Paths, Stroke Paths, etc... They are generated at the canvas resolution and don't change with the canvas resolution being changed after the fact.
I feel like I could probably explain it more clearly but hopefully you got the answers to your questions in there somewhere :)
- Charlie