feat(control_tree): Phase 131 P1.5-P2 DirectValue exit reconnection

Implement DirectValue mode for Normalized shadow exit handling:

**P1.5 Changes**:
- Add ExitReconnectMode::DirectValue (skip exit PHI generation)
- Carry remapped_exit_values through merge result
- Update host variable_map directly with exit values
- Fix loop(true) { x = 1; break }; return x to return 1 correctly

**P2 Changes**:
- Normalize k_exit continuation entry/exit edges
- Rewrite TailCall(k_exit) → Jump(exit_block) for proper merge
- Add verify_all_terminator_targets_exist contract check
- Extend ExitLineReconnector to handle DirectValue mode

**Infrastructure**:
- tools/build_llvm.sh: Force TMPDIR under target/ (EXDEV mitigation)
- llvm_exe_runner.sh: Add exit_code verification support
- Phase 131 smokes: Update for dev-only + exit code validation

**Contracts**:
- PHI-free: Normalized path uses continuations only
- Exit values reconnect via remapped ValueIds
- Existing patterns unaffected (既定挙動不変)

Related: Phase 131 loop(true) break-once Normalized support

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tools/smokes/v2/lib/llvm_exe_runner.sh

@@ -191,3 +191,62 @@ llvm_exe_build_and_run_numeric_smoke() {
   printf "%s\n" "$EXPECTED"
   return 1
 }
+
+llvm_exe_build_and_run_expect_exit_code() {
+  # Required globals:
+  # - INPUT_HAKO
+  # - OUTPUT_EXE
+  # - EXPECTED_EXIT_CODE
+  #
+  # Optional:
+  # - LLVM_BUILD_LOG
+  # - RUN_TIMEOUT_SECS
+
+  if [ -z "${INPUT_HAKO:-}" ] || [ -z "${OUTPUT_EXE:-}" ] || [ -z "${EXPECTED_EXIT_CODE:-}" ]; then
+    echo "[FAIL] llvm_exe_build_and_run_expect_exit_code: missing INPUT_HAKO/OUTPUT_EXE/EXPECTED_EXIT_CODE"
+    return 1
+  fi
+
+  mkdir -p "$(dirname "$OUTPUT_EXE")"
+
+  echo "[INFO] Building: $INPUT_HAKO → $OUTPUT_EXE"
+
+  local cargo_target_dir
+  cargo_target_dir="$(llvm_exe_cargo_target_dir)"
+
+  # Ensure we use the compiler binary built in that target dir.
+  local nyash_bin="$cargo_target_dir/release/hakorune"
+  local obj_out="$cargo_target_dir/aot_objects/$(basename "$INPUT_HAKO").o"
+  mkdir -p "$(dirname "$obj_out")"
+
+  local build_log="${LLVM_BUILD_LOG:-/tmp/llvm_exe_build.log}"
+  if ! env CARGO_TARGET_DIR="$cargo_target_dir" NYASH_BIN="$nyash_bin" NYASH_LLVM_OBJ_OUT="$obj_out" NYASH_DISABLE_PLUGINS=0 \
+    "$NYASH_ROOT/tools/build_llvm.sh" "$INPUT_HAKO" -o "$OUTPUT_EXE" 2>&1 | tee "$build_log"; then
+    echo "[FAIL] build_llvm.sh failed"
+    tail -n 80 "$build_log"
+    return 1
+  fi
+
+  if [ ! -x "$OUTPUT_EXE" ]; then
+    echo "[FAIL] Executable not created or not executable: $OUTPUT_EXE"
+    ls -la "$OUTPUT_EXE" 2>/dev/null || echo "File does not exist"
+    return 1
+  fi
+
+  echo "[INFO] Executing: $OUTPUT_EXE"
+
+  set +e
+  local output
+  output=$(timeout "${RUN_TIMEOUT_SECS:-10}" env NYASH_DISABLE_PLUGINS=0 "$OUTPUT_EXE" 2>&1)
+  local exit_code=$?
+  set -e
+
+  if [ "$exit_code" -ne "$EXPECTED_EXIT_CODE" ]; then
+    echo "[FAIL] Execution exit code mismatch: got $exit_code, expected $EXPECTED_EXIT_CODE"
+    echo "[INFO] Raw output (tail):"
+    echo "$output" | tail -n 80
+    return 1
+  fi
+
+  return 0
+}