feat(normalization): Phase 142 P0 - Statement-level normalization

## Summary

Changed normalization unit from "block suffix" to "statement (loop only)"
to prevent pattern explosion.

## Changes

1. **PlanBox** (`plan_box.rs`):
   - Always return `loop_only()` for any `loop(true)`, regardless of what follows
   - Subsequent statements (return, assignments) handled by normal MIR lowering
   - ~70 lines reduced, 7 unit tests updated

2. **build_block** (`stmts.rs`):
   - Removed `break` after consumed=1 from suffix_router
   - Continue processing subsequent statements normally
   - Phase 142 P0 comments added

3. **Tests**:
   - Fixture: `phase142_loop_stmt_only_then_return_length_min.hako`
   - VM smoke: exit code 3 (s="abc" → s.length() → 3)

## Results

- ✅ Unit tests: 10/10 passed
- ✅ Phase 142 VM smoke: PASS
- ✅ Phase 131 regression: PASS
- ✅ Build: Success

## Design

- **Pattern Explosion Prevention**: Normalize only the loop (consumed=1)
- **Out-of-Scope Policy**: Always Ok(None) for fallback
- **Fail-Fast**: Only for "in-scope but broken" cases

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

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

tools/smokes/v2/profiles/integration/apps/phase142_loop_stmt_only_then_return_length_min_vm.sh

@@ -0,0 +1,56 @@
+#!/bin/bash
+# Phase 142 P0: Loop normalization as single statement (VM)
+#
+# Verifies that loop(true) normalization returns consumed=1, allowing
+# subsequent statements (return s.length()) to be processed normally.
+# Expected: exit code 3 (s="abc" → s.length() → 3)
+#
+# Dev-only: NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1
+
+source "$(dirname "$0")/../../../lib/test_runner.sh"
+export SMOKES_USE_PYVM=0
+require_env || exit 2
+
+# Phase 142 is a dev-only Normalized shadow loop case
+require_joinir_dev
+
+PASS_COUNT=0
+FAIL_COUNT=0
+RUN_TIMEOUT_SECS=${RUN_TIMEOUT_SECS:-10}
+
+echo "[INFO] Phase 142 P0: Loop normalization as single statement (VM)"
+
+# Test 1: phase142_loop_stmt_only_then_return_length_min.hako
+echo "[INFO] Test 1: phase142_loop_stmt_only_then_return_length_min.hako"
+INPUT="$NYASH_ROOT/apps/tests/phase142_loop_stmt_only_then_return_length_min.hako"
+
+set +e
+OUTPUT=$(timeout "$RUN_TIMEOUT_SECS" env \
+  NYASH_DISABLE_PLUGINS=1 \
+  "$NYASH_BIN" --backend vm "$INPUT" 2>&1)
+EXIT_CODE=$?
+set -e
+
+if [ "$EXIT_CODE" -eq 124 ]; then
+  echo "[FAIL] hakorune timed out (>${RUN_TIMEOUT_SECS}s)"
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+elif [ "$EXIT_CODE" -eq 3 ]; then
+  # Phase 142: expected output is exit code 3 (s.length() where s="abc")
+  echo "[PASS] exit code verified: 3"
+  PASS_COUNT=$((PASS_COUNT + 1))
+else
+  echo "[FAIL] hakorune failed with exit code $EXIT_CODE (expected 3)"
+  echo "[INFO] output (tail):"
+  echo "$OUTPUT" | tail -n 50 || true
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+fi
+
+echo "[INFO] PASS: $PASS_COUNT, FAIL: $FAIL_COUNT"
+
+if [ "$FAIL_COUNT" -eq 0 ]; then
+  test_pass "phase142_loop_stmt_only_then_return_length_min_vm: All tests passed"
+  exit 0
+else
+  test_fail "phase142_loop_stmt_only_then_return_length_min_vm: $FAIL_COUNT test(s) failed"
+  exit 1
+fi