fix(env): improve Environment::set scope resolution (partial)

Fixed:
- Environment::set now properly searches ancestor chain before creating new binding
- Added exists_in_chain_locked() helper for explicit existence checking
- Simple {} blocks now correctly update outer scope variables

Verified Working:
- local x = 10; { x = 42 }; print(x) → prints 42 ✅

Still Broken:
- else blocks don't update outer scope variables
- local x = 10; if flag { x = 99 } else { x = 42 }; print(x) → prints 10 ❌

Root Cause Identified:
- Issue is in MIR Builder (compile-time), not Environment (runtime)
- src/mir/builder/if_form.rs:108 resets variable_map before else block
- PHI generation at merge doesn't use else_var_map_end correctly
- MIR shows: phi [%32, bb1], [%1, bb2] where %1 is original value, not else value

Next: Fix else block variable merging in if_form.rs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

tools/smokes/v2/profiles/integration/parity/vm_llvm_scope_assign.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+ROOT_DIR="$(cd "$SCRIPT_DIR/../../../../../.." && pwd)"
+source "$ROOT_DIR/tools/smokes/v2/lib/test_runner.sh" || true
+source "$ROOT_DIR/tools/smokes/v2/lib/result_checker.sh" || true
+
+require_env || { echo "[SKIP] env not ready"; exit 0; }
+
+test_vm_llvm_scope_assign() {
+  local code='static box Main { method main(args) { local x = 0 { if (1==1) { x = 42 } } return x } }'
+  # Stage-3 parse is required for `local`
+  NYASH_PARSER_STAGE3=1 check_parity -c "$code" "vm_llvm_scope_assign"
+}
+
+run_test "vm_llvm_scope_assign" test_vm_llvm_scope_assign

tools/smokes/v2/profiles/quick/core/phase215/scope_assign_vm.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+set -uo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+ROOT_DIR="$(cd "$SCRIPT_DIR/../../../../../../.." && pwd)"
+source "$ROOT_DIR/tools/smokes/v2/lib/test_runner.sh" || true
+source "$ROOT_DIR/tools/smokes/v2/lib/result_checker.sh" || true
+
+require_env || { echo "[SKIP] env not ready"; exit 0; }
+
+test_scope_assign_vm() {
+  local code='static box Main { method main(args) { local x = 0 { if (1==1) { x = 42 } } return x } }'
+  local tmp
+  tmp=$(mktemp --suffix .hako)
+  printf '%s' "$code" > "$tmp"
+  # Quick: VM should reflect nested assignment
+  local rc
+  NYASH_PARSER_STAGE3=1 "$NYASH_BIN" --backend vm "$tmp" >/dev/null 2>&1
+  rc=$?
+  if [[ "$rc" -ne 42 ]]; then
+    echo "[FAIL] scope_assign_vm: vm rc=$rc (expected 42)"
+    return 1
+  fi
+  echo "[PASS] scope_assign_vm"
+  rm -f "$tmp" 2>/dev/null || true
+  return 0
+}
+
+run_test "scope_assign_vm" test_scope_assign_vm

tools/smokes/v2/profiles/quick/core/phase215/stageb_scope_extract_canary.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+ROOT="$(cd "$(dirname "$0")/../../../../../.." && pwd)"
+BIN="$ROOT/target/release/hakorune"
+
+if [[ ! -x "$BIN" ]]; then
+  echo "[SKIP] hakorune not built"; exit 0
+fi
+
+# Source with nested assignment; Stage-B should extract body or at least output Program JSON
+SRC='static box Main { method main(args) { local x = 0 { if (1==1) { x = 42 } } return x } }'
+
+out=$(NYASH_ENABLE_USING=1 HAKO_ENABLE_USING=1 "$BIN" --backend vm "$ROOT/lang/src/compiler/entry/compiler_stageb.hako" -- --source "$SRC" 2>/dev/null || true)
+
+echo "$out" | grep -q '"kind":"Program"' || { echo "[FAIL] stageb_scope_extract_canary: no Program JSON"; exit 1; }
+
+# Heuristic check: JSON contains at least a numeric literal 42 somewhere
+echo "$out" | grep -q '42' || { echo "[FAIL] stageb_scope_extract_canary: literal 42 not found"; exit 1; }
+
+echo "[PASS] stageb_scope_extract_canary"
+