How to cache cargo-vcpkg dependencies?

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I'm trying to use cargo-chef for a project that is using [cargo-vcpkg](https://github.com/mcgoo/cargo-vcpkg) for building C++ dependencies.

Is this use case possible with cargo-chef? The following doesn't seem to have the caching effect I'd like since it rebuilds the C++ dependencies every time I make a change.

```
FROM chef AS ffi
COPY . .
RUN cargo vcpkg --verbose build --manifest-path subcrate/Cargo.toml

FROM chef AS planner
COPY . .
RUN cargo chef prepare --recipe-path recipe.json

FROM chef AS builder
COPY --from=planner /build/recipe.json recipe.json
COPY --from=ffi /build/target target

RUN cargo chef cook --recipe-path recipe.json

COPY . .
RUN cargo build --bin subcrate
```

The vcpkg build seems to require copying in the workspace Cargo.toml and the subcrate Cargo.toml and code as well, which is why I'm using 'COPY . .' in the ffi layer

Start by reproducing the shown Docker stages with cargo-vcpkg and cargo-chef using the workspace Cargo.toml, subcrate/Cargo.toml, recipe.json, and target directory. Compare which COPY inputs invalidate the ffi layer when source files change. Done means the documented approach preserves the C++ dependency cache across ordinary Rust source changes.

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