diff --git a/lang/src/llvm_ir/emit/README.md b/lang/src/llvm_ir/emit/README.md
new file mode 100644
index 00000000..937161d0
--- /dev/null
+++ b/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.
diff --git a/lang/src/mir/builder/README.md b/lang/src/mir/builder/README.md
new file mode 100644
index 00000000..63a8ffc7
--- /dev/null
+++ b/lang/src/mir/builder/README.md
@@ -0,0 +1,22 @@
+# MirBuilderBox — Program(JSON v0) → MIR(JSON v0)
+
+Responsibility
+- Convert Stage‑B Program(JSON v0) into MIR(JSON v0) for VM/LLVM lines.
+- Phase 20.34 starts with a delegate implementation to Runner and progressively internalizes ops.
+
+Interface (stable)
+- `emit_from_program_json_v0(program_json: String, opts: Map|Null) -> String|Null`
+  - Returns canonical MIR(JSON v0) on success; returns null and prints a tagged diagnostic on failure.
+
+Tags (Fail‑Fast, stable)
+- `[mirbuilder/input/null]` — input is null
+- `[mirbuilder/input/invalid]` — header missing (version/kind)
+- `[mirbuilder/delegate]` — delegate path selected (Runner `--program-json-to-mir`)
+- `[mirbuilder/delegate/missing]` — delegate/provider not wired yet
+
+Toggles (default OFF)
+- `HAKO_MIR_BUILDER_DELEGATE=1`: Use Runner `--program-json-to-mir` as a temporary provider
+
+Notes
+- Box‑First policy: boundary/contract first, then implementation. Keep tags stable; no silent fallback.
+- Large payloads: implementation may stream/json-scan later; initial version is string‑based.
diff --git a/nyash.toml b/nyash.toml
index 3f1c05f4..215c1344 100644
--- a/nyash.toml
+++ b/nyash.toml
@@ -152,6 +152,10 @@ path = "lang/src/shared/common/string_helpers.hako"
 "hakorune.vm.mir_min" = "lang/src/vm/boxes/mir_vm_min.hako"
 "hakorune.vm.core" = "lang/src/vm/boxes/mini_vm_core.hako"
 
+# Phase 20.34 — Box‑First selfhost build line (aliases for Hako boxes)
+"hako.mir.builder" = "lang/src/mir/builder/MirBuilderBox.hako"
+"hako.llvm.emit" = "lang/src/llvm_ir/emit/LLVMEmitBox.hako"
+
 # Temporary alias keys removed (Phase‑20.33 TTL reached). Use `selfhost.shared.*` above.
 
 # v2 Plugin libraries (loader reads these for TypeBox ABI)