restore(lang): full lang tree from ff3ef452 (306 files) — compiler, vm, shared, runner, c-abi, etc.\n\n- Restores lang/ directory (files≈306, dirs≈64) as per historical branch with selfhost sources\n- Keeps our recent parser index changes in compiler/* (merged clean by checkout)\n- Unblocks selfhost development and documentation references

lang/src/tools/runner_front/LAYER_GUARD.hako

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+#![doc = "Phase 20.13 runner_front guard — define layer responsibilities."]
+
+static box RUNNER_FRONT_GUARD {
+  name() { return "runner_front" }
+  allowed_imports() { return ["json", "cli", "env"] }
+  forbidden_imports() { return ["vm_core", "llvm", "plugins"] }
+}
+

lang/src/tools/runner_front/README.md

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+# runner_front — Script-built Front EXE (Phase 20.13)
+
+Purpose
+- Decide runner mode and normalize inputs before core execution.
+- Replace Rust-side front logic via a thin, testable EXE (AOT built from Hakorune scripts).
+
+Notes (AOT / Single‑EXE)
+- 本モジュールは将来、単一の hakorune.exe に内蔵（AOT）され、同一プロセス内で呼び出されます。
+- 開発時は tools/front_exe/runner_front.sh をゲートONで差し替え可能（1行契約の互換を維持）。
+
+Responsibilities
+- Parse CLI/ENV relevant to backend/mode/entry.
+- Produce a short verdict and exit code:
+  - OK: adopt decision (prints normalized JSON or token) and exit 0
+  - NOOP: no decision; Rust runner proceeds with legacy path, exit 0
+  - FAIL: stable tag, exit non‑zero (no fallback by design)
+
+Inputs/Outputs (contract)
+- Input: CLI args + ENV (documented below)
+- Output: one short line (OK/NOOP/FAIL + payload or tag) to stdout
+- Exit codes: 0=adopt/noop, 1=fail
+
+ENV (planned; default OFF)
+- HAKO_RUNNER_USE_SCRIPT_EXE=1 (alias NYASH_*) — enable front EXE adoption
+- HAKO_QUIET=1 — silence noisy logs (front adheres to quiet)
+
+Non‑Goals
+- No plugin/ABI routing here (handled downstream)
+- No semantics; runner_front only decides and normalizes
+
+TTL / Removal Plan
+- Runner boundary diagnostics/tags are temporary; migrate to core/front over time.