This repo now points me to sdk/src/canisters/frontend/ic-frontend-canister at master · dfinity/sdk · GitHub, which doesn’t have the source code implementation.
Looking at crates.io: Rust Package Registry points me to GitHub - dfinity/cdk-rs: Rust canister development kit for the Internet Computer., and I’m assuming the assets canister is somewhere in https://github.com/dfinity/cdk-rs/tree/main/library/ic-certified-map?
Note that this half-hearted struggle in trying to find the current Asset Canister source code is coming from someone with no experience in Rust other than hello world, but I’m curious since @sea-snake just made some improvements to agent-js, adding an AssetManager to the 0.14.0 release.