fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

lang/src/runtime/gc/gc_box.hako

@@ -6,31 +6,31 @@
 static box GcBox {
   // Return JSON string with counters {safepoints, barrier_reads, barrier_writes}
   stats() {
-    return call("env.gc.stats/0")
+    return gc.stats()
   }
 
   // Return total roots count (host handles + modules), best‑effort integer
   roots_snapshot() {
-    return call("env.gc.roots_snapshot/0")
+    return gc.roots_snapshot()
   }
 
   // Request collection (no‑op until host supports it)
   collect() {
     // Host may ignore; keep Fail‑Fast if extern missing
-    call("env.gc.collect/0")
+    gc.collect()
   }
 
   // Optional lifecycle hooks (no‑op unless host implements)
-  start() { call("env.gc.start/0"); }
-  stop() { call("env.gc.stop/0"); }
+  start() { gc.start(); }
+  stop() { gc.stop(); }
 
   // Example (dev): a tiny cadence policy, OFF by default.
   // Enable with: HAKO_GC_POLICY_TICK=1 (docs only; call manually from scripts)
   policy_tick() {
-    if (call("env.local.get/1", "HAKO_GC_POLICY_TICK") == "1") {
+    if (env.get("HAKO_GC_POLICY_TICK") == "1") {
       // Read metrics and print a compact line for observation
       local s = me.stats()
-      call("env.console.log/1", "[GcBox] stats=" + s)
+      console.log("[GcBox] stats=" + s)
       // Example threshold (no-op unless host implements collect):
       // me.collect()
     }
@@ -41,12 +41,12 @@ static box GcBox {
   // HAKO_GC_POLICY_FORCE=1     → call collect() each tick (may be no-op; guard expected)
   // HAKO_GC_POLICY_EVERY_N=K   → best-effort modulus trigger (tick_count % K == 0)
   tick_with_policy(tick_count) {
-    local log = call("env.local.get/1", "HAKO_GC_POLICY_LOG")
-    local every = call("env.local.get/1", "HAKO_GC_POLICY_EVERY_N")
-    local force = call("env.local.get/1", "HAKO_GC_POLICY_FORCE")
+    local log = env.get("HAKO_GC_POLICY_LOG")
+    local every = env.get("HAKO_GC_POLICY_EVERY_N")
+    local force = env.get("HAKO_GC_POLICY_FORCE")
 
     if (log == "1") {
-      call("env.console.log/1", "[GcBox] stats=" + me.stats())
+      console.log("[GcBox] stats=" + me.stats())
     }
     if (force == "1") {
       // Gate: host may not implement collect() yet