Install wasm32v1-none target at container runtime

[leighmcculloch]

What

Add rustup target add wasm32v1-none to entrypoint.sh so the target is installed against whichever Rust toolchain is active inside the running container, after cd /source honors any rust-toolchain.toml in the mounted project.

Why

The Docker image runs rustup target add wasm32v1-none at image-build time, which only installs the target for the toolchain that was the default in rust:latest when the image was built. When a contract pins a different Rust toolchain (via rust-toolchain.toml, rustup override, or RUST_TOOLCHAIN), rustup auto-installs that toolchain inside the container without the wasm32v1-none target, causing builds to fail with:

error[E0463]: can't find crate for `core`
  = note: the `wasm32v1-none` target may not be installed

Installing the target at runtime, after cd /source, ensures rustup resolves the toolchain the project actually requires and adds the target to it. rustup target add is a no-op when the target is already present, so the default-toolchain case is unaffected.

This is also a blocker for #2506 (--docker option for reproducible builds).

Close #2545

Known limitations

N/A

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[Copilot]

Pull request overview

This PR updates the Docker image entrypoint so wasm32v1-none is installed at container runtime, aiming to ensure the target is added for whichever Rust toolchain is active inside the mounted project (e.g., when rust-toolchain.toml pins a non-default toolchain).

Changes:

• Add a new entrypoint.sh that runs rustup target add wasm32v1-none before executing the CLI command.
• Update Dockerfile to copy the new entrypoint script and set it as the container ENTRYPOINT (wrapping stellar).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
entrypoint.sh	New runtime entrypoint that installs the wasm target then execs the requested command.
Dockerfile	Switches container entrypoint to the new script and adjusts binary permissions/copy steps.