Phase 20.34 prep: add using aliases in nyash.toml for hako.mir.builder & hako.llvm.emit; add README contracts for MirBuilderBox/LLVMEmitBox; verify canaries green

lang/src/llvm_ir/emit/README.md

@@ -0,0 +1,27 @@
+# LLVMEmitBox — MIR(JSON v0) → Object (.o)
+
+Responsibility
+- Generate an object file from MIR(JSON v0) via a provider.
+- Phase 20.34 starts with a provider‑first stub; connects to a Plugin v2 wrapper for ny-llvmc (or llvmlite) next.
+
+Interface (stable)
+- `emit_object(mir_json: String, opts: Map|Null) -> String|Null`
+  - Returns output path string on success; returns null with a tagged diagnostic on failure.
+
+Tags (Fail‑Fast, stable)
+- `[llvmemit/input/null]` — input is null
+- `[llvmemit/input/invalid]` — missing `functions`/`blocks`
+- `[llvmemit/provider/missing]` — no provider hint
+- `[llvmemit/provider/unsupported] <name>` — unsupported provider name
+- `[llvmemit/ny-llvmc/not-found]` — ny-llvmc not found (planned)
+- `[llvmemit/ny-llvmc/failed status=N]` — ny-llvmc returned non‑zero (planned)
+- `[llvmemit/skip] provider stub; implement Plugin v2 call` — current stub behavior
+
+Toggles (default OFF)
+- `HAKO_LLVM_EMIT_PROVIDER=ny-llvmc|llvmlite` — select provider
+- `HAKO_LLVM_OPT_LEVEL=0..3` — optimization level (provider‑side)
+- `HAKO_LLVM_TIMEOUT_MS=60000` — process timeout (provider‑side)
+
+Notes
+- Box‑First: keep provider behind a single Plugin v2 method `LLVMCodegenBox.emit_object/2`.
+- Environments must not change defaults silently; Fail‑Fast with stable tags.