# Phase 20.9 — Rust‑less Kernel via Hakorune → LLVM → C ABI

Goal
- Remove Rust from the runtime execution path (kernel) by driving calls from Hakorune scripts through the LLVM line to a thin C ABI.
- Keep plugins/HostBridge/loader in Rust (unchanged). Only the kernel path becomes Rust‑optional.

Scope (this phase)
- Read‑only GC externs: `env.gc.stats/0` (JSON string), `env.gc.roots_snapshot/0` (i64).
- Utilities (minimal): console log/warn/error, time (now_ms), local env (`env.local.get`), string bridging (handle ⇄ i8*).
- Control hooks (collect/start/stop): defined + gated; may be no‑ops or Fail‑Fast until implemented.

Out‑of‑Scope (keep Rust)
- Plugin loader/registries, HostBridge v1 router, high‑level Box/Type systems.

Why
- Thin‑Rust policy: keep data plane (traversal/barriers/safepoints) out of the critical policy loop.
- Self‑hosting: make collection cadence/logging scriptable in Hakorune (GcBox).

Key Docs
- Checklist: ./CHECKLIST.md
- Tasks & Rules: ./TASKS.md
- C‑ABI bridge plan: ../../../development/architecture/abi/hakorune-c-abi-bridge.md
- LLVM extern plan (GC): ../../../development/architecture/gc/llvm-extern-plan.md
- Policy vs Data Plane: ../../../development/architecture/gc/policy-vs-data-plane.md

Acceptance (MVP)
- Hakorune `call("env.gc.stats/0")` and `call("env.gc.roots_snapshot/0")` reach C symbols under `--backend llvm` (gated canaries PASS).
- GcBox.stats()/roots_snapshot() return same shape across VM/LLVM (read‑only parity). PASS
- collect/start/stop exist as gated calls; do not silently fallback; emit short diagnostics. PASS

Gates & Safety
- All new paths default OFF; enable via smoke gates/environment.
- Diagnostics use short, stable lines (NOT_FOUND/UNSUPPORTED/VALIDATION). Quiet mode suppresses short lines.
- In EXE mode, linker diagnostics are normalized to short lines (`SMOKES_ERR: symbol_missing[:name]`); set `SMOKES_KEEP_LD=1` to keep full LD output.
- CI STRICT: tooling scripts accept `CI_STRICT=1` to upgrade WARN to FAIL (e.g., header path canonical check, dotted symbol check).

STRICT Plan (flip criteria)
- Stage 1 (current): WARN-only
  - Scripts: `tools/ci/check_header_canonical.sh`, `tools/ci/checks/aot_dotted_symbol_check.sh`
  - Aggregator: `tools/ci/run_local_checks.sh` (use locally; no GitHub integration yet)
- Stage 2 (pre‑flip): Dry-run in CI for ≥1 サイクル、false positive を除去
- Stage 3 (flip to STRICT): `CI_STRICT=1` で FAIL に昇格
  - 前提: ドキュメント/修正例が揃い、既知の例外が0件

Risks & Rollback
- Ownership/memory rules (char* free) must be strictly documented and adhered.
- If LLVM canary fails (symbols missing), keep gates OFF; VM path remains unaffected.
- Rollback is trivial: remove/disable C shims; VM continues to function.