Runtime syscall ownership and ABI boundary

Purpose

Define execution-level ownership for runtime ABI entrypoints, platform syscalls, and backend neutrality.

Boundary invariants

1. Runtime owns platform behavior (syscall, OS API, blocking policy).
2. JIT and AOT import the same runtime ABI surface.
3. Frontend/lowering MUST NOT encode backend-specific syscall behavior.
4. Stdlib-facing APIs remain stable while runtime internals evolve.

ABI ownership split

• Language-level Extern syntax and typing: docs/spec/ffi-and-extern.md.
• Runtime symbol/link/loading behavior: this document.
• Stdlib API-level contracts: docs/standard-library/.

Runtime-mediated execution model

• System-facing stdlib operations call stable runtime ABI entrypoints.
• Runtime implements Linux/OS-specific details internally.
• Optional interop dispatcher symbols may exist for language/runtime interop boundaries.

Required guarantees

• Backends preserve ABI parity across JIT and AOT.
• Runtime symbol/signature divergence is a compatibility break.
• User-facing docs must not expose internal __interop_* implementation details.

Maintenance rules

• Runtime ABI surface changes require versioned compatibility handling.
• Platform-policy changes belong in runtime docs and implementation only.
• Backend docs may reference runtime ABI usage but must not redefine runtime ownership.

References

• docs/execution/runtime/runtime-overview.md
• docs/execution/runtime/ffi.md
• docs/execution/architecture/jit-aot-boundary.md