Hybrid Selfhost Build (80/20)

Purpose
- Provide a minimal, fast path to compile Hako source via Hakorune Stage‑B to Program(JSON v0), and optionally run it via Core‑Direct (in‑proc).
- Future: add MIR emit and ny-llvmc EXE build in small increments.

Script
- tools/selfhost/selfhost_build.sh
  - --in <file.hako>: input Hako source
  - --json <out.json>: write Program(JSON v0); default: /tmp/hako_stageb_$$.json
  - --mir <out.json>: emit MIR(JSON) from source (runner path)
  - --exe <out>: build native executable via ny-llvmc (llvmlite harness)
  - --run: run via Gate‑C/Core Direct (in‑proc). Exit code mirrors program return.
  - Env:
    - NYASH_BIN: path to hakorune/nyash binary (auto-detected)
    - NYASH_ROOT: repo root (auto-detected)
    - HAKO_USE_BUILDBOX=1: use BuildBox for emit-only (no run/exe)

Examples
```bash
# Emit JSON only (Stage‑B)
tools/selfhost/selfhost_build.sh --in apps/demo/main.hako --json /tmp/demo.json

# Run and use exit code
tools/selfhost/selfhost_build.sh --in apps/demo/return7.hako --run; echo $?
```

Notes
- Stage‑B emit uses either the Stage‑B entry or BuildBox（HAKO_USE_BUILDBOX=1 for emit-only）
- Runner executes Core‑Direct in-proc under HAKO_CORE_DIRECT_INPROC=1.
- For heavier cases (bundles/alias/require), keep Stage‑B canaries opt‑in in quick profile.

---

Stage1 Selfhost Binary (Phase 25.1 — initial wiring)

Purpose
- Provide a concrete Stage1 binary (`hakorune`) built from Hako sources.
- Separate the Rust bootstrap binary (Stage0, `nyash`) from the Hakorune selfhost binary at the build-script level.

Script
- tools/selfhost/build_stage1.sh
  - Builds a Stage1 selfhost executable from a Nyash/Hako entry point.
  - Current entry (default):
    - `lang/src/runner/launcher.hako` — Stage1 CLI launcher (commands: emit program-json/mir-json, etc.).
  - Output:
    - `target/selfhost/hakorune` by default.

Usage
```bash
# Build Stage1 selfhost binary with defaults
tools/selfhost/build_stage1.sh

# Custom output path
tools/selfhost/build_stage1.sh --out /tmp/hakorune-dev

# Custom entry (experimental)
tools/selfhost/build_stage1.sh --entry apps/selfhost-minimal/main.hako --out /tmp/hako_min
```

How it works
- Pipeline:
  1) Stage‑B + MirBuilder:
     - `tools/hakorune_emit_mir.sh <entry.hako> <mir.json>`
  2) LLVM EXE build:
     - `tools/ny_mir_builder.sh --in <mir.json> --emit exe -o <exe>`
- The Rust binary (Stage0) is resolved via the existing helpers inside `hakorune_emit_mir.sh` / `ny_mir_builder.sh`:
  - Prefers `target/release/hakorune` when present.
  - Falls back to `target/release/nyash` otherwise.

Notes
- This Stage1 binary is a minimal Ny Executor and not yet a full CLI replacement.
- Full CLI / mode selection for Stage1 will be implemented in later phases; this script focuses on establishing the binary layout and build wiring.