# Phase 20.26 — Final Rust Consolidation + hakmem (Plan)

Purpose
- Consolidate remaining Rust lines to Floor-only responsibilities and move legacy backends to archive with deprecations.
- Keep day-to-day defaults unchanged and green; all flips are opt-in and guarded.

Scope (Phase 20.26)
- Deprecate and archive legacy Rust LLVM (inkwell) backend; prefer ny-llvmc (llvmlite harness).
- Keep Rust as Floor (CLI, I/O, process, FFI) and shift decision/normalization to Hakorune boxes where feasible.
- Add small helper gates for memory (hakmem) without changing defaults.

Non-Goals
- No default behavior changes for users. No removal of legacy code without a full deprecation window (1 release).
- No broad refactor of working paths outside agreed guardrails.

Workstreams
1) Deprecation warnings (inkwell)
   - Print a one-time deprecate banner when feature `llvm-inkwell-legacy` path executes.
   - Docs: mark inkwell as legacy and point to ny-llvmc.

2) Archive and gate (inkwell)
   - Move `src/backend/llvm/compiler/**` → `archive/legacy/llvm-inkwell/**` (paths preserved via `#[path]` when feature active).
   - Keep feature gates and tests green; no behavior change.

3) Runner plan adoption (thin)
   - Introduce `RunnerPlanBuilder` in lang: build a plan (decision only). Rust applies the plan.
   - Start as opt-in (`HAKO_RUNNER_PLAN=1`), no behavior change by default.
   - v0: action ExecuteCore/ExecuteVM を適用（Gate‑C/VM）。ExecuteNyLlvmc/Boxes は advisory（将来拡張）。

4) hakmem integration (gate only)
   - Keep libc as default allocator. Provide `--mem hakmem`/`HAKO_C_ABI_ALLOC=hakmem` placeholder route.
   - No functional switch yet; only routing and docs.

Milestones
- M1 (A): Deprecation banner + docs scaffold + CURRENT_TASK updated
- M2 (B): Archive move, feature-gated paths compile; quick stays green
- M3 (C): RunnerPlan opt-in wiring; no default change
- M4 (D): hakmem gate documented and observed (no default flip)

Risks & Mitigations
- Risk: Path drift between archived code and callers → Mitigate with `#[path]` glue and feature tests.
- Risk: Surprise behavior changes → Keep all flips opt-in; add stable tags; Fail-Fast on ambiguity.

Toggles (ENV/CLI)
- `--vm-backend llvm|vm|mir` (ENV: `HAKO_VM_BACKEND`) — unchanged
- `HAKO_LLVM_USE_HARNESS=1` — prefer ny-llvmc harness path
- `HAKO_C_ABI_ALLOC={libc|hakmem}` — allocator gate (default: libc)
- `HAKO_RUNNER_PLAN=1` — opt-in RunnerPlan path (decision in lang; v0 は ExecuteCore/ExecuteVM のみ適用)

Acceptance (Phase 20.26 complete)
- quick/integration green with defaults unchanged
- inkwell path prints deprecate banner when used; harness path preferred in docs
- legacy LLVM code archived and feature-gated; build remains green
- docs updated (README/PLAN/CHECKLIST, env toggles, migration notes)