Build can embed the wrong runtime after switching Pulley feature

Summary

Switching between native and Pulley builds can embed the wrong hyperlight-wasm-runtime guest. A native host build can retain the Pulley runtime and reject a valid x86 AOT component:

GuestError(GuestError, "Module was compiled for architecture 'x86_64'")

Reproduction

Use a consumer feature that enables hyperlight-wasm/pulley.

1. Build and run with an x86 AOT component.
2. Build and run with the Pulley feature and a Pulley AOT component.
3. Build and run with the x86 AOT component again.

The third run can reject the x86 component. This reproduces with hyperlight-wasm 0.15.0 and Wasmtime 36.0.14.

Root cause

hyperlight-wasm/build.rs builds the embedded runtime into a shared nested target directory:

<target>/hyperlight-wasm-runtime/x86_64-hyperlight-none/<profile>/hyperlight-wasm-runtime

Native and Pulley Cargo units have separate OUT_DIR directories. Both generated wasm_runtime_resource.rs files use include_bytes! with this shared mutable path.

The nested Pulley build overwrites the runtime binary. Cargo can rebuild the native hyperlight-wasm unit because the include_bytes! input changed while its build script remains cached. The native unit then embeds the Pulley binary.

The shared output also permits a race between concurrent normal and Pulley builds.

Suggested fix

Copy the completed nested runtime into the outer build script's OUT_DIR. Point include_bytes! at that private copy. This preserves the shared nested compilation cache.

Concurrent builds also need one of these protections:

• Hold a lock across the nested build and copy.
• Use a separate nested target directory for each runtime configuration.

The configuration key must cover pulley, gdb, trace_guest, wasmtime_latest, and the WIT environment values. The outer OUT_DIR provides complete isolation but duplicates compilation work.

Regression coverage

Build a consumer in both sequences. Verify that the final component loads:

normal -> pulley -> normal
pulley -> normal -> pulley

Concurrent native and Pulley builds should produce correctly matched embedded runtimes.

Start in hyperlight-wasm/build.rs and inspect how the nested runtime output and generated wasm_runtime_resource.rs use OUT_DIR and the shared target path. Reproduce the normal -> pulley -> normal and pulley -> normal -> pulley consumer sequences, then exercise concurrent native and Pulley builds. Done means each AOT component loads with its matching embedded runtime and concurrent builds remain correctly isolated.