Phase 20.34: add MirBuilderBox + LLVMEmitBox (Hako, delegate/provider stubs with stable tags); add quick canaries (phase2034) for presence and SKIP policy; update phase docs + CURRENT_TASK

lang/src/mir/builder/MirBuilderBox.hako

@@ -0,0 +1,46 @@
+// MirBuilderBox — Program(JSON v0) → MIR(JSON v0)
+// Contract (Phase 20.34, staged):
+// - I/F is stable; implementation starts as a delegate to Runner path.
+// - Unsupported or unavailable paths must Fail‑Fast with stable tags (no silent fallback).
+//
+// API
+// - emit_from_program_json_v0(program_json: String, opts: Map|Null) -> String|Null
+//   Returns MIR(JSON v0) on success, or prints a tag and returns null on failure/skip.
+//
+// Toggles (delegate first):
+// - HAKO_MIR_BUILDER_DELEGATE=1 — implementation delegated to Runner (--program-json-to-mir).
+//   In this initial stub, we only indicate delegation via a stable tag.
+
+static box MirBuilderBox {
+  // Availability probe (for canaries)
+  is_available() {
+    // For now, availability means delegate toggle is present
+    local t = env.get("HAKO_MIR_BUILDER_DELEGATE")
+    if t == null { return 0 }
+    if ("" + t) == "1" { return 1 } else { return 0 }
+  }
+
+  // Main entry
+  emit_from_program_json_v0(program_json, opts) {
+    if program_json == null {
+      print("[mirbuilder/input/null] program_json is null")
+      return null
+    }
+    // Minimal validation: must include version/kind
+    local s = "" + program_json
+    if !(s.contains("\"version\"")) || !(s.contains("\"kind\"")) {
+      print("[mirbuilder/input/invalid] missing version/kind keys")
+      return null
+    }
+    // Delegate-first policy (Phase 20.34 Milestone A)
+    local d = env.get("HAKO_MIR_BUILDER_DELEGATE")
+    if d != null && ("" + d) == "1" {
+      print("[mirbuilder/delegate] use Runner --program-json-to-mir")
+      return null
+    }
+    // Provider not wired yet
+    print("[mirbuilder/delegate/missing] no provider; enable HAKO_MIR_BUILDER_DELEGATE=1")
+    return null
+  }
+}
+