refactor(normalization): Phase 135 P0 - Extend plan to zero post-loop assigns

Generalize NormalizationPlan suffix detection to accept zero post-loop assignments:

Goal: Improve entry point consistency by allowing `loop + assign* + return` (N >= 0)

Implementation:
- Modified plan_box.rs detection logic (only file changed)
- Removed `post_assign_count >= 1` requirement
- Unified Phase 131 (loop + return) and Phase 132-133 (loop + assign+ + return) paths

Changes:
- src/mir/builder/control_flow/normalization/plan_box.rs:
  - Removed assignment count constraint
  - Unified pattern detection: `loop + assign* + return` (N >= 0)
- apps/tests/phase135_loop_true_break_once_post_empty_return_min.hako (new fixture)
- tools/smokes/v2/profiles/integration/apps/phase135_*.sh (new smoke tests)

Pattern support:
- Phase 131/135: loop + return only (consumed: 2, post_assign_count: 0) ✅
- Phase 132: loop + 1 assign + return (consumed: 3, post_assign_count: 1) ✅
- Phase 133: loop + N assigns + return (consumed: 2+N, post_assign_count: N) ✅

Design principles maintained:
- **Minimal change**: Only plan_box.rs modified (execute_box unchanged)
- **SSOT**: Detection logic centralized in plan_box.rs
- **Box-First**: Responsibility separation preserved (Plan/Execute)

Test results:
- Unit tests (plan_box): 9/9 PASS (2 new tests added)
- Phase 135 VM/LLVM EXE: PASS (exit code 1)
- Phase 131 regression: 2/2 PASS (path now unified)
- Phase 133 regression: 2/2 PASS
- cargo test --lib: PASS

Benefits:
- Unified entry point for all loop + post patterns
- Easier maintenance (single detection logic)
- Future extensibility (easy to add new patterns)
- Clear separation of Phase 131 and Phase 132-135 paths

Default behavior unchanged: Dev-only guard maintained

Related: Phase 135 normalization pattern consistency improvement

🤖 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/phase135_loop_true_break_once_post_empty_return_llvm_exe.sh

@@ -0,0 +1,38 @@
+#!/bin/bash
+# Phase 135 P0: loop(true) break-once + return (0 post assigns, LLVM EXE parity)
+# Pattern: loop(true) { x = 1; break } → return x (should be 1)
+
+source "$(dirname "$0")/../../../lib/test_runner.sh"
+source "$(dirname "$0")/../../../lib/llvm_exe_runner.sh"
+export SMOKES_USE_PYVM=0
+require_env || exit 2
+
+llvm_exe_preflight_or_skip || exit 0
+
+# Phase 135 is a dev-only Normalized shadow loop case.
+# LLVM EXE emission must run with JoinIR dev/strict enabled, otherwise it will freeze.
+require_joinir_dev
+
+# Phase 135: minimal plugin set (StringBox, ConsoleBox, IntegerBox only)
+STRINGBOX_SO="$NYASH_ROOT/plugins/nyash-string-plugin/libnyash_string_plugin.so"
+CONSOLEBOX_SO="$NYASH_ROOT/plugins/nyash-console-plugin/libnyash_console_plugin.so"
+INTEGERBOX_SO="$NYASH_ROOT/plugins/nyash-integer-plugin/libnyash_integer_plugin.so"
+
+LLVM_REQUIRED_PLUGINS=(
+  "StringBox|$STRINGBOX_SO|nyash-string-plugin"
+  "ConsoleBox|$CONSOLEBOX_SO|nyash-console-plugin"
+  "IntegerBox|$INTEGERBOX_SO|nyash-integer-plugin"
+)
+LLVM_PLUGIN_BUILD_LOG="/tmp/phase135_loop_true_break_once_post_empty_return_plugin_build.log"
+llvm_exe_ensure_plugins_or_fail || exit 1
+
+INPUT_HAKO="$NYASH_ROOT/apps/tests/phase135_loop_true_break_once_post_empty_return_min.hako"
+OUTPUT_EXE="$NYASH_ROOT/tmp/phase135_loop_true_break_once_post_empty_return_llvm_exe"
+
+EXPECTED_EXIT_CODE=1
+LLVM_BUILD_LOG="/tmp/phase135_loop_true_break_once_post_empty_return_build.log"
+if llvm_exe_build_and_run_expect_exit_code; then
+  test_pass "phase135_loop_true_break_once_post_empty_return_llvm_exe: exit code matches expected (1)"
+else
+  exit 1
+fi

tools/smokes/v2/profiles/integration/apps/phase135_loop_true_break_once_post_empty_return_vm.sh

@@ -0,0 +1,54 @@
+#!/bin/bash
+# Phase 135 P0: loop(true) break-once + return (0 post assigns, Normalized shadow, VM)
+#
+# Verifies that loop(true) { <assign>* ; break } + return (0 assigns) works:
+# - x = 0 → loop(true) { x = 1; break } → return x → 1
+# - Dev-only: NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1
+
+source "$(dirname "$0")/../../../lib/test_runner.sh"
+export SMOKES_USE_PYVM=0
+require_env || exit 2
+
+# Phase 135 is a dev-only Normalized shadow loop case.
+require_joinir_dev
+
+PASS_COUNT=0
+FAIL_COUNT=0
+RUN_TIMEOUT_SECS=${RUN_TIMEOUT_SECS:-10}
+
+echo "[INFO] Phase 135 P0: loop(true) break-once + return (0 post assigns, Normalized shadow, VM)"
+
+# Test 1: phase135_loop_true_break_once_post_empty_return_min.hako
+echo "[INFO] Test 1: phase135_loop_true_break_once_post_empty_return_min.hako"
+INPUT="$NYASH_ROOT/apps/tests/phase135_loop_true_break_once_post_empty_return_min.hako"
+
+set +e
+OUTPUT=$(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 1 ]; then
+  # Phase 135: expected output is exit code 1 (return value)
+  echo "[PASS] exit code verified: 1"
+  PASS_COUNT=$((PASS_COUNT + 1))
+else
+  echo "[FAIL] hakorune failed with exit code $EXIT_CODE (expected 1)"
+  echo "[INFO] output (tail):"
+  echo "$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 "phase135_loop_true_break_once_post_empty_return_vm: All tests passed"
+  exit 0
+else
+  test_fail "phase135_loop_true_break_once_post_empty_return_vm: $FAIL_COUNT test(s) failed"
+  exit 1
+fi