feat(parser): Phase 285A1.4 & A1.5 - Weak field sugar + Parser hang fix

A1.4: Add sugar syntax `public weak parent` ≡ `public { weak parent }`
A1.5: Fix parser hang on unsupported `param: Type` syntax

Key changes:
- A1.4: Extend visibility parser to handle weak modifier (fields.rs)
- A1.5: Shared helper `parse_param_name_list()` with progress-zero detection
- A1.5: Fix 6 vulnerable parameter parsing loops (methods, constructors, functions)
- Tests: Sugar syntax (OK/NG), parser hang (timeout-based)
- Docs: lifecycle.md, EBNF.md, phase-285a1-boxification.md

Additional changes:
- weak() builtin implementation (handlers/weak.rs)
- Leak tracking improvements (leak_tracker.rs)
- Documentation updates (lifecycle, types, memory-finalization, etc.)

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

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

docs/guides/testing-guide.md

@@ -218,6 +218,42 @@ Nyash provides a macro-powered lightweight test runner in Phase 16 (MVP).
   - `nyash --run-tests apps/tests/my_tests.hako`
   - Discovers top-level `test_*` functions and Box `test_*` methods (static/instance).
 - Filtering: `--test-filter NAME` (substring match) or env `NYASH_TEST_FILTER`.
+
+---
+
+## Phase 285: Lifecycle / WeakRef / Leak diagnostics（クロスバックエンド）
+
+言語SSOT:
+- `docs/reference/language/lifecycle.md`（`fini` / weak / cleanup / GC方針）
+- `docs/reference/language/types.md`（truthiness と `null`/`void`）
+
+目的:
+- Rust VM と LLVM（harness）で、weak と lifecycle の挙動が一致しているかを短い fixture で固定する。
+- 強参照サイクル等で「終了時に強参照rootが残っている」状況を、default-off の診断で観測できるようにする（実装後）。
+
+推奨の運用（ルート汚染防止）:
+- fixture は `local_tests/` に置く。
+
+例（weakが効いていること）:
+```bash
+mkdir -p local_tests
+$EDITOR local_tests/phase285_weak_basic.hako
+
+./target/release/hakorune --backend vm local_tests/phase285_weak_basic.hako
+NYASH_LLVM_USE_HARNESS=1 ./target/release/hakorune --backend llvm local_tests/phase285_weak_basic.hako
+```
+
+例（強参照サイクル + 終了時診断）:
+```bash
+$EDITOR local_tests/phase285_cycle.hako
+
+# 実装後: leak report をONにして終了時に root を表示
+NYASH_LEAK_LOG=1 ./target/release/hakorune --backend vm local_tests/phase285_cycle.hako
+NYASH_LLVM_USE_HARNESS=1 NYASH_LEAK_LOG=1 ./target/release/hakorune --backend llvm local_tests/phase285_cycle.hako
+```
+
+実装者向けの詳しい手順:
+- `docs/development/current/main/phases/phase-285/CLAUDE_CODE_RUNBOOK.md`
 - Entry policy when a main exists:
   - `--test-entry wrap` → run tests then call original main
   - `--test-entry override` → replace entry with test harness only