[v1][breaking] Compiler.Compile and Loader.GetReader should accept a context

[robbyt]

Summary

The two core interfaces don't accept a context.Context:

• platform/script/compiler.go:17-29 — Compile(scriptReader io.ReadCloser)
• platform/script/loader/loader.go:9-12 — GetReader() (io.ReadCloser, error)

This causes three concrete problems today:

1. The Extism compiler stores ctx on the struct via a WithContext option (engines/extism/compiler/compiler.go:17, engines/extism/compiler/options.go:96-104), which is racy if a Compiler is shared across goroutines.

2. The Risor inner compile hard-codes context.Background() (engines/risor/compiler/internal/compile/compile.go:21), so caller cancellation is ignored entirely.

3. HTTP compile can hang indefinitely because ExecutableUnit calls GetReader() (platform/script/executableUnit.go:61), not GetReaderWithContext. The HTTP loader has the context-aware variant but nothing reaches for it.

Proposal

• Compile(ctx context.Context, r io.ReadCloser) (ExecutableContent, error)
• GetReader(ctx context.Context) (io.ReadCloser, error) — drop the GetReaderWithContext helper as redundant.
• Delete WithContext from the Extism compiler.
• Plumb the context through NewExecutableUnit so the loader call gets the same one.

Files

• platform/script/compiler.go
• platform/script/loader/loader.go
• platform/script/loader/{fromHTTP,fromBytes,fromString,fromIoReader,fromDisk}.go
• platform/script/executableUnit.go
• engines/{extism,risor,starlark}/compiler/compiler.go
• engines/risor/compiler/internal/compile/compile.go
• engines/extism/compiler/options.go (remove WithContext)

This is a breaking-change candidate for v1.