feat(joinir): Phase 53 - SELFHOST-NORM-DEV-EXPAND implementation

Expanded selfhost dev Normalized target with 2 practical P2/P3 loop variations,
strengthened structural signature axis, and implemented two-stage detection.

Key Changes:

1. Documentation (phase49-selfhost-joinir-depth2-design.md +128 lines):
   - Added Phase 53 section with candidate selection rationale
   - Documented two-stage detector strategy (structural primary + dev-only name guard)
   - Defined structural axis strengthening (carrier count/type, branch patterns)

2. Fixtures (+210 lines):
   - selfhost_args_parse_p2.program.json (60 lines): P2 with String carrier + conditional branching
   - selfhost_stmt_count_p3.program.json (150 lines): P3 with 5 carriers + multi-branch if-else

3. Structured Builders (fixtures.rs +48 lines):
   - build_selfhost_args_parse_p2_structured_for_normalized_dev()
   - build_selfhost_stmt_count_p3_structured_for_normalized_dev()

4. ShapeGuard Two-Stage Detection (shape_guard.rs +80 lines):
   - Added SelfhostArgsParseP2/SelfhostStmtCountP3 to NormalizedDevShape enum
   - Implemented is_selfhost_args_parse_p2(): P2 core family + name guard
   - Implemented is_selfhost_stmt_count_p3(): 2-10 carrier check + name guard
   - Updated capability_for_shape() mappings

5. Bridge Integration (bridge.rs +8 lines, normalized.rs +10 lines):
   - Added shape handlers delegating to existing normalizers
   - Added roundtrip reconstruction handlers

6. Entry Point Registration (ast_lowerer/mod.rs +2 lines):
   - Registered selfhost_args_parse_p2/selfhost_stmt_count_p3 as LoopFrontend routes

7. Dev VM Comparison Tests (normalized_joinir_min.rs +40 lines):
   - normalized_selfhost_args_parse_p2_vm_bridge_direct_matches_structured()
   - normalized_selfhost_stmt_count_p3_vm_bridge_direct_matches_structured()

8. Test Context Fix (dev_env.rs):
   - Added thread-local test context depth counter
   - Fixed deadlock in nested test_ctx() calls via reentrant with_dev_env_if_unset()

Structural Axis Growth:

P2 family:
- Carrier count: 1-3 (unchanged)
- NEW: Type diversity (Integer/String mixed)
- NEW: Conditional branching patterns (Eq-heavy comparisons)

P3 family:
- NEW: Carrier count upper bound: 2-10 (was 2-4)
- NEW: Multi-branch if-else (5+ branches with nested structure)
- NEW: Complex conditional patterns

Test Results:
- normalized_dev: 40/40 PASS (including 2 new tests)
- lib regression: 939 PASS, 56 ignored
- Existing behavior unchanged (normalized_dev feature-gated)

Phase 53 Achievements:
✅ P2/P3 each gained 1 practical variation (2 total)
✅ Two-stage detection: structural primary + dev-only name guard
✅ Structural axis expanded: 4 axes (carrier count/type/Compare/branch patterns)
✅ All tests PASS, no regressions
✅ Test context deadlock fixed (0.04s for 29 tests)

Files Modified: 14 files
Lines Added: ~516 lines (net)
Implementation: Pure additive (feature-gated)

Next Phase (54+):
- Accumulate 6+ loops per P2/P3 family
- Achieve 5+ stable structural axes
- Target < 5% false positive rate
- Then shrink/remove name guard scope

docs/development/current/main/phase48-norm-p4-design.md

@@ -1,7 +1,7 @@
 # Phase 48: Normalized P4 (Continue) Design
 
-**Status**: Design Phase (doc-only)
-**Date**: 2025-12-12
+**Status**: Phase 48-A/B/C COMPLETE (minimal + JsonParser skip_ws continue、Normalized→MIR 直経路＋canonical 昇格まで完了)
+**Date**: 2025-12-12 / 2026-01-XX
 
 ## Goal
 
@@ -213,6 +213,22 @@ struct Pattern4Env {
 
 **Goal**: Prove P4 can use Normalized infrastructure with minimal additions.
 
+**実装ステータス（48-A 完了サマリ）**:
+
+- ✅ Fixture 追加: `pattern4_continue_min.program.json`
+  - 「`i == 2` を `continue` でスキップする最小 P4 ループ」を Program(JSON) として用意。
+- ✅ ShapeGuard 拡張:
+  - `NormalizedDevShape::Pattern4ContinueMinimal` を追加し、構造ベースで P4 minimal 形状を検出。
+- ✅ StepScheduleBox 拡張:
+  - `StepKind::ContinueCheck` を追加し、評価順序を  
+    `HeaderCond → ContinueCheck → Updates → Tail` に固定。
+- ✅ Normalized lowering:
+  - `normalize_pattern4_continue_minimal()` を実装し、P2 正規化ロジックを 95% 再利用した continue 対応を追加。
+- ✅ テスト:
+  - Normalized dev スイートに P4 minimal 用の比較テストを 4 本追加  
+    （Structured→Normalized→MIR(direct) vs Structured→MIR / runner / VM bridge）。
+  - `cargo test --release` ベースで **939/939 tests PASS**（Phase 48-A 実装時点）。
+
 **Steps**:
 1. **ShapeGuard**: Add `Pattern4ContinueMinimal` shape
 2. **StepScheduleBox**: Add `ContinueCheck` step kind
@@ -232,7 +248,11 @@ struct Pattern4Env {
 
 ### Phase 48-B: _parse_object, _unescape_string (dev-only)
 
-**Goal**: Extend to multiple carriers, string operations.
+**Status (dev-only)**: `_parse_array` / `_parse_object` の whitespace continue ループを Normalized→MIR(direct) で比較済み。  
+Fixture を `jsonparser_parse_{array,object}_continue_skip_ws.program.json` として追加し、shape_guard / normalize_for_shape / direct bridge で dev 専用ルートを通す。  
+_unescape_string は未着手（Phase 48-C 以降）。
+
+**Goal**: Extend to multiple carriers, string operations (unescape) after skip_ws 系が固まったら続行。
 
 **Additions**:
 - Multi-carrier EnvLayout (if needed)
@@ -319,11 +339,13 @@ count = 4  (skipped i==2, so counted 0,1,3,4)
 ## Success Criteria
 
 **Phase 48-A complete when**:
-1. ✅ `test_normalized_pattern4_continue_minimal` passes (dev-only)
-2. ✅ Structured→Normalized→MIR(direct) output matches Structured→MIR
-3. ✅ All 938+ tests still pass (no regressions)
-4. ✅ ShapeGuard can detect Pattern4ContinueMinimal
-5. ✅ Documentation updated (architecture overview, CURRENT_TASK)
+1. `test_normalized_pattern4_continue_minimal` passes (dev-only)
+2. Structured→Normalized→MIR(direct) output matches Structured→MIR
+3. All 938+ tests still pass (no regressions)
+4. ShapeGuard can detect Pattern4ContinueMinimal
+5. Documentation updated (architecture overview, CURRENT_TASK)
+
+→ 上記 1–5 はコミット `7200309c` 時点ですべて満たされており、Phase 48-A は完了ステータスだよ。
 
 **Phase 48-B complete when**:
 1. ✅ _parse_object, _unescape_string tests pass (dev-only)