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/development/current/main/phases/phase-285/phase-285a1-boxification.md

@@ -180,9 +180,140 @@ Phase 285A1 は Phase 285 の一部として、weak field 処理の基盤を整
 
 **Note**: weak field 構文（`weak next: Node`）は未実装。Phase 285 P1 で実装予定。
 
+---
+
+## A1.5: Parser Hang Fix - Parameter Type Annotations ✅
+
+**Status**: ✅ Complete (2025-12-24)
+
+### Problem
+
+During Phase 285A1.4 implementation, discovered critical parser bug:
+- User writes: `setParent(p: Node) { ... }`
+- Parser hangs infinitely at COLON token (no advance on unexpected token)
+- Workaround required removing type annotation → `setParent(p) { ... }` → Works
+
+### Root Cause
+
+**6 identical vulnerable parameter parsing loops** across the parser codebase:
+1. `src/parser/declarations/box_def/members/methods.rs:21-30`
+2. `src/parser/declarations/box_def/members/constructors.rs:27-34` (init)
+3. `src/parser/declarations/box_def/members/constructors.rs:101-108` (pack)
+4. `src/parser/declarations/box_def/members/constructors.rs:138-145` (birth)
+5. `src/parser/items/functions.rs:34-51`
+6. `src/parser/items/static_items.rs:72-87`
+
+**Vulnerable Code Pattern**:
+```rust
+while !p.match_token(&TokenType::RPAREN) && !p.is_at_end() {
+    must_advance!(p, _unused, "method parameter parsing");
+    if let TokenType::IDENTIFIER(param) = &p.current_token().token_type {
+        params.push(param.clone());
+        p.advance();  // ← Only advances on IDENTIFIER
+    }
+    // ⚠️ COLON token: not IDENTIFIER, not COMMA, not RPAREN → NO ADVANCE → INFINITE LOOP
+    if p.match_token(&TokenType::COMMA) {
+        p.advance();
+    }
+}
+```
+
+**EBNF Spec Finding**: `params` grammar undefined in EBNF.md, `:` TYPE is for return type only
+
+### Solution: Shared Helper Function (DRY Principle)
+
+Created `src/parser/common/params.rs` with common parameter parsing logic:
+
+```rust
+/// Parse parameter name list with Fail-Fast on unexpected tokens
+///
+/// Parses: IDENT (',' IDENT)*
+/// Rejects: Type annotations, unexpected tokens, malformed comma sequences
+pub(crate) fn parse_param_name_list(
+    p: &mut NyashParser,
+    context: &str,  // "method", "constructor", "function" for error messages
+) -> Result<Vec<String>, ParseError>
+```
+
+**Key Features**:
+- **Progress-zero detection**: Tracks token position, errors if stuck (prevents infinite loops)
+- **Explicit token handling**: All token types (IDENTIFIER, COMMA, other) explicitly matched
+- **Fail-Fast**: Either advances or errors (no infinite loop possible)
+- **Unified error messages**: Context parameter customizes messages per call site
+
+### Files Modified
+
+**New Files** (2):
+- `src/parser/common/params.rs` (~90 lines) - Helper function
+- `tools/smokes/v2/profiles/quick/parser/phase285_param_type_annotation_nohang.sh` - Timeout smoke test
+
+**Modified Files** (8):
+1. `src/parser/common/mod.rs` - Module declaration (moved common.rs → common/mod.rs)
+2. `src/parser/declarations/box_def/members/methods.rs` - Replaced 12 lines with 1 call
+3. `src/parser/declarations/box_def/members/constructors.rs` - Replaced 3 loops (init/pack/birth)
+4. `src/parser/items/functions.rs` - Replaced 20 lines with 2 lines
+5. `src/parser/items/static_items.rs` - Replaced 22 lines with 2 lines
+6. `apps/tests/phase285_parser_param_type_annot_should_not_hang.hako` - Regression test
+
+**Net Change**: +90 new - 72 removed + 6 calls = **+24 lines** (with better error handling!)
+
+### Tests
+
+**Regression Test**: `apps/tests/phase285_parser_param_type_annot_should_not_hang.hako`
+```hako
+box TestNode {
+    value: IntegerBox
+    // ❌ Should error immediately (type annotation not supported)
+    setParent(p: Node) {
+        return 0
+    }
+}
+```
+
+**Smoke Test**: `tools/smokes/v2/profiles/quick/parser/phase285_param_type_annotation_nohang.sh`
+- Timeout: 3 seconds (detects hang)
+- Expected: Parse error within 1 second
+- Validation: Error message mentions "Unexpected token COLON" and "Parameter type annotations not supported"
+
+**Result**: ✅ PASS
+```
+✅ PASS: Parser correctly rejects param type annotations without hanging
+```
+
+### Error Message Examples
+
+**Before** (infinite hang):
+```
+🚨 PARSER INFINITE LOOP DETECTED at method parameter parsing
+```
+
+**After** (clear error):
+```
+❌ Parse error: Unexpected token COLON, expected ',' or ')' in method parameter list.
+Note: Parameter type annotations are not supported.
+```
+
+### Architecture Benefits
+
+**DRY Principle**:
+- **Before**: 6 identical vulnerable loops (72 lines total)
+- **After**: 1 helper function (~90 lines) + 6 one-line calls
+
+**Maintainability**:
+- Future fixes only need 1 location
+- Unified error messages (single source of truth)
+- Progress-zero detection guaranteed in one place
+
+**Safety**:
+- No infinite loop possible (Fail-Fast guaranteed)
+- All token types explicitly handled (no silent fallthrough)
+- Context-aware error messages (better UX)
+
 ## References
 
 - Phase 33: Box Theory Modularization ([phase-33-modularization.md](../../../architecture/phase-33-modularization.md))
 - Phase 285: Box lifecycle ([phase-285/README.md](README.md))
-- `src/mir/builder/weak_field_validator.rs`: 実装本体
-- `src/mir/builder/fields.rs`: 呼び出し側
+- `src/mir/builder/weak_field_validator.rs`: A1.1 実装本体
+- `src/mir/builder/fields.rs`: A1.1 呼び出し側
+- `src/parser/common/params.rs`: A1.5 実装本体
+- `src/parser/declarations/box_def/members/fields.rs`: A1.2-A1.4 実装本体