Phase 25.1a: selfhost builder hotfix (fn rename, docs)

tools/selfhost/README.md

@@ -29,3 +29,45 @@ 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.