feat(phase21.5): MirBuilder optimization prep + crate EXE infrastructure

Phase 21.5 optimization readiness - C-level performance target:
- MirBuilder: JsonFrag purify toggle (HAKO_MIR_BUILDER_JSONFRAG_PURIFY=1)
- Normalizer: extended f64 canonicalization + dedupe improvements
- loop_opts_adapter: JsonFrag path refinement for crate EXE compatibility

Infrastructure improvements:
- provider_registry: add diagnostics + ring-1 providers (array/console/map/path)
- mir_interpreter: add normalization/purify feature gates
- tools/selfhost_exe_stageb.sh: new end-to-end Stage-B→crate EXE pipeline
- tools/perf/microbench.sh: performance measurement tooling

Smoke tests (phase2100):
- Extend timeout 15s→120s for heavy crate EXE builds
- Add stageb_loop_jsonfrag_crate_exe_canary_vm.sh (target test)
- Add s3_backend_selector_crate_exe_vm_parity_return42_canary_vm.sh

Documentation:
- ENV_VARS.md: add Phase 21.5 optimization toggles
- README updates: clarify crate backend strategy
- phase215-optimization.md: new optimization roadmap

This commit sets the stage for Phase 21.5 critical optimization:
achieving C-level performance to decide hakorune's future viability.

lang/src/mir/builder/MirBuilderBox.hako

@@ -52,6 +52,18 @@ static box MirBuilderBox {
       local internal = env.get("HAKO_MIR_BUILDER_INTERNAL")
       local internal_on = (internal == null) || (("" + internal) == "1")
       if internal_on == 1 {
+        // Dev-only: force loop JSONFrag minimal output (pre-optimization bring-up)
+        // Guard: HAKO_MIR_BUILDER_LOOP_FORCE_JSONFRAG=1
+        {
+          local f = env.get("HAKO_MIR_BUILDER_LOOP_FORCE_JSONFRAG")
+          if f != null && ("" + f) == "1" {
+            local mir = "{\"functions\":[{\"name\":\"main\",\"params\":[],\"locals\":[],\"blocks\":[" +
+              "{\"id\":0,\"instructions\":[{\"op\":\"const\",\"dst\":1,\"value\":{\"type\":\"i64\",\"value\":0}},{\"op\":\"const\",\"dst\":2,\"value\":{\"type\":\"i64\",\"value\":0}},{\"op\":\"compare\",\"operation\":\"<\",\"lhs\":1,\"rhs\":2,\"dst\":3},{\"op\":\"branch\",\"cond\":3,\"then\":1,\"else\":2}]}," +
+              "{\"id\":1,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}," +
+              "{\"id\":2,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}]}]}"
+            return norm_if(mir)
+          }
+        }
         // Optional: registry-driven lowering (scaffold). When HAKO_MIR_BUILDER_REGISTRY=1,
         // iterate PatternRegistryBox.candidates() and dispatch by name.
         // NOTE: using/alias は prelude で解決される（位置に依存しない）。

lang/src/mir/builder/internal/README.md

@@ -1,22 +1,12 @@
-# MirBuilder Internal Boxes — Minimal Shapes (Phase 20.34)
+MirBuilder Internals — Toggle Aggregation
 
-Responsibility
-- Provide small, readable boxes that lower a very small subset of Program(JSON v0)
-  into MIR(JSON v0) strings without heavy parsing. Fail‑Fast with stable tags.
+- Use `builder_config_box.hako` (`hako.mir.builder.internal.builder_config`) to read all `HAKO_MIR_BUILDER_*` toggles.
+- Do not call `env.get` directly in lowers; prefer helper methods like:
+  - `trace_enabled()`, `debug_enabled()`
+  - `internal_on()`, `registry_on()`, `registry_only()`
+  - `loop_jsonfrag_on()`, `jsonfrag_normalize_on()`, `skip_loops_on()`
+  - `loop_adapter_return_mode()` → `string` (default) or `map`
 
-Boxes
-- `prog_scan_box.hako` — tiny helpers for string scanning: find, skip spaces, read quoted/op/int values.
-- `lower_return_int_box.hako` — Return(Int N) → const(i64 N) + ret.
-- `lower_return_binop_box.hako` — Return(Binary(Int,Int) op {+,-,*,/}) → const, const, binop, ret.
-- `lower_if_compare_box.hako` — If(Compare(Int,Int) then Return(Int) else Return(Int)) → compare, branch, ret×2.
-- `lower_loop_simple_box.hako` — Loop(Compare i<limit) counting loop（i=0..limit）→ LoopFormBox.loop_count に委譲。
-- `lower_loop_sum_bc_box.hako` — Loop sum + break/continue 哲学（i==break → break / i==skip → continue）→ LoopFormBox.build("sum_bc", ...)。
+Notes
+- JsonFrag emission is kept default OFF and used for structural observation only. Semantics are prioritized by the normal path.
 
-Policy
-- No execution or I/O; emit-only. Keep shapes minimal and obvious. For unsupported inputs, print
-  `[mirbuilder/internal/unsupported] ...` and return null.
-
-LoopForm param
-- LoopFormBox.build(mode, limit, skip, break)
-  - mode: "count"（i を返す）/ "sum_bc"（sum の合流を Exit PHI で返す）
-  - limit/skip/break は i64 として扱う。skip/break は null の場合、`skip=2` / `break=limit` を既定とする。

lang/src/mir/builder/internal/builder_config_box.hako

@@ -0,0 +1,44 @@
+// builder_config_box.hako — Centralized env/toggles for MirBuilder
+// Purpose: avoid scattered env.get calls. All HAKO_MIR_BUILDER_* toggles are read here.
+
+static box BuilderConfigBox {
+  // Generic on/off reader for HAKO_MIR_BUILDER_* flags
+  _is_on(key) {
+    local v = env.get(key)
+    if v == null { return 0 }
+    local s = "" + v
+    if s == "1" || s == "true" || s == "on" { return 1 }
+    return 0
+  }
+
+  // Trace controls
+  trace_enabled() { return self._is_on("HAKO_MIR_BUILDER_TRACE") }
+  debug_enabled() { return self._is_on("HAKO_MIR_BUILDER_DEBUG") || self._is_on("NYASH_CLI_VERBOSE") }
+
+  // Registry and internal lowers
+  internal_on() {
+    local v = env.get("HAKO_MIR_BUILDER_INTERNAL")
+    // default ON
+    return (v == null) || ("" + v == "1")
+  }
+  registry_on() {
+    local v = env.get("HAKO_MIR_BUILDER_REGISTRY")
+    // default ON
+    return (v == null) || ("" + v == "1")
+  }
+  registry_only() { return env.get("HAKO_MIR_BUILDER_REGISTRY_ONLY") }
+
+  // Loop/JsonFrag related
+  loop_jsonfrag_on() { return self._is_on("HAKO_MIR_BUILDER_LOOP_JSONFRAG") }
+  jsonfrag_normalize_on() { return self._is_on("HAKO_MIR_BUILDER_JSONFRAG_NORMALIZE") }
+  skip_loops_on() { return self._is_on("HAKO_MIR_BUILDER_SKIP_LOOPS") }
+
+  // Return-mode for loop adapter: "string" (default) | "map"
+  loop_adapter_return_mode() {
+    local m = env.get("HAKO_MIR_BUILDER_LOOP_RETURN")
+    if m == null { return "string" }
+    local s = "" + m
+    if s == "string" { return "string" }
+    return "map"
+  }
+}

lang/src/mir/builder/internal/jsonfrag_normalizer_box.hako

@@ -39,6 +39,8 @@ static box JsonFragNormalizerBox {
     local const_list = new ArrayBox()
     local others_list = new ArrayBox()
     local seen = new MapBox()  // signature -> 1
+    // Dev-only: purify flag to drop builder-side allocations (e.g., newbox) from JSONFrag output
+    local purify = 0; { local pv = env.get("HAKO_MIR_BUILDER_JSONFRAG_PURIFY"); if pv != null { local pvs = "" + pv; if pvs == "1" { purify = 1 } } }
     loop(i < n) {
       guard = guard + 1
       if guard > 4096 { break }
@@ -52,6 +54,9 @@ static box JsonFragNormalizerBox {
       i = ob_end + 1
       // classify by op
       local op = JsonFragBox.get_str(obj, "op")
+      if purify == 1 {
+        if op == "newbox" { continue }
+      }
       if op == "phi" {
         phi_list.push(obj)
         continue

lang/src/mir/builder/internal/loop_opts_adapter_box.hako

@@ -2,6 +2,8 @@
 // Purpose: centralize MapBox creation/set so that we can later swap to JsonFrag-based
 // construction without touching all callers.
 
+using "hako.mir.builder.internal.builder_config" as BuilderConfigBox
+
 static box LoopOptsBox {
   new_map() {
     return new MapBox()
@@ -16,8 +18,7 @@ static box LoopOptsBox {
     using selfhost.shared.common.string_helpers as StringHelpers
     using "hako.mir.builder.internal.jsonfrag_normalizer" as JsonFragNormalizerBox
     // Opt-in: minimal MIR(JSON) construction for structure validation
-    local jf = env.get("HAKO_MIR_BUILDER_LOOP_JSONFRAG")
-    if jf != null && ("" + jf) == "1" {
+    if BuilderConfigBox.loop_jsonfrag_on() == 1 {
       // Read limit if present, else default to 0 (safe)
       local limit = opts.get("limit"); if limit == null { limit = 0 }
       // Normalize to string
@@ -31,11 +32,15 @@ static box LoopOptsBox {
           "{\"op\":\"branch\",\"cond\":3,\"then\":1,\"else\":2}]}," +
         "{\"id\":1,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}," +
         "{\"id\":2,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}]}]}"
-      print("[mirbuilder/internal/loop:jsonfrag]")
+      if BuilderConfigBox.trace_enabled() == 1 { print("[mirbuilder/internal/loop:jsonfrag]") }
       // Optional: normalization (dev toggle)
-      local norm = env.get("HAKO_MIR_BUILDER_JSONFRAG_NORMALIZE")
-      if norm != null && ("" + norm) == "1" {
-        return JsonFragNormalizerBox.normalize_all(mir)
+      if BuilderConfigBox.jsonfrag_normalize_on() == 1 { mir = JsonFragNormalizerBox.normalize_all(mir) }
+      // Return mode: default string, optionally wrap into Map
+      local mode = BuilderConfigBox.loop_adapter_return_mode()
+      if mode == "map" {
+        local m = self.new_map()
+        m = self.put(m, "mir", mir)
+        return m
       }
       return mir
     }

lang/src/mir/builder/internal/lower_loop_simple_box.hako

@@ -8,6 +8,7 @@ using selfhost.shared.json.utils.json_frag as JsonFragBox
 using "hako.mir.builder.internal.pattern_util" as PatternUtilBox
 using "hako.mir.builder.internal.loop_scan" as LoopScanBox
 using "hako.mir.builder.internal.loop_opts_adapter" as LoopOptsBox
+using "hako.mir.builder.internal.builder_config" as BuilderConfigBox
 
 static box LowerLoopSimpleBox {
   try_lower(program_json) {
@@ -59,8 +60,7 @@ static box LowerLoopSimpleBox {
 
     // JsonFrag 直組立（opt-in）: HAKO_MIR_BUILDER_LOOP_JSONFRAG=1
     {
-      local jf = env.get("HAKO_MIR_BUILDER_LOOP_JSONFRAG")
-      if jf != null && ("" + jf) == "1" {
+      if BuilderConfigBox.loop_jsonfrag_on() == 1 {
         // Minimal MIR(JSON) with compare + branch + ret（構造検証用）
         // Note: semanticsは簡略（canaryはトークン検出のみ）
         local mir = "{\"functions\":[{\"name\":\"main\",\"params\":[],\"locals\":[],\"blocks\":[" +
@@ -71,7 +71,7 @@ static box LowerLoopSimpleBox {
             "{\"op\":\"branch\",\"cond\":3,\"then\":1,\"else\":2}]}," +
           "{\"id\":1,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}," +
           "{\"id\":2,\"instructions\":[{\"op\":\"ret\",\"value\":1}]}]}]}"
-        print("[mirbuilder/internal/loop:jsonfrag]")
+        if BuilderConfigBox.trace_enabled() == 1 { print("[mirbuilder/internal/loop:jsonfrag]") }
         return mir
       }
     }