Walking Skeleton — Real Program Slice

Goal

Prove the production spine from the shared executable-program artifact through bytecode and the VM to the real CLI, without creating a second realization pipeline.

Implementation Sketch

Create a dedicated ori_vm crate with unsafe_code = "deny", depending only on backend-neutral compiler/runtime crates.
Add VmBackend beside LlvmBackend at the existing backend boundary. It consumes the canonical ExecutableProgram; it does not call ARC lowering, canonicalization, or method/derive discovery itself.
Use a deliberately small provisional encoding and safe typed slots. The slice includes straight-line arithmetic plus one call target outside the ordinary-function cache (an impl method, derive, or built-in descriptor) so the closed-program prerequisite is actually tested.
Expose the slice through the existing backend selector as ori run --backend=vm. Keep --dual as a diagnostic mode, not a separate realization path.
Compare stdout, stderr class, exit status, and leak counters with the tree-walker and LLVM. A missing callable must fail cleanly rather than panic or fall through to LLVM.

Layer Coverage

Layer	Disposition
L1	N/A: no grammar changes.
L2	N/A: no typechecking changes.
L3	N/A: no canonicalization changes.
L4	Covered by the skeleton post-AIMS artifact criterion.
L5	Covered by the VM execution criterion.
L6	Covered by the LLVM-debug backend-selection regression criterion.
L7	Covered by the LLVM-release backend-selection regression criterion.
L8	Covered by the AOT backend-selection regression criterion.
L9	Covered by the section cross-executor criterion.
L10	Covered by the section leak-freedom criterion.
L11	Covered by the skeleton spec-fixture criterion.
L12	Covered by the real `ori run --backend=vm` criterion.

Work Items

Scaffold safe ori_vm plus VmBackend at the existing backend boundary; consume the canonical executable-program artifact and add provisional typed slots/encoding without a second ARC path.
Drive arithmetic plus a non-ordinary callable through real ori run --backend=vm; assert output, exit, parity, and leak behavior and fail cleanly for an intentionally missing callable.