docs: Phase 142 P2 Step 3-B design decisions fixed

- Pattern5 handles return (not Pattern4) - prevents bloat as parse_*/continue family expands
- ExitMeta expansion NOT needed initially - return ends function, no carrier reconnect needed
- Return payload self-contained within Pattern5 (temporary/direct return, no phi merge)
- ContinueReturn asset reuse: extract consistency checks only (not exit_line machinery)
- Implementation checklist prepared for next session

🤖 Generated with Claude Code

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

docs/development/current/main/phases/phase-142/README.md

@@ -455,11 +455,62 @@ The following patterns are rejected with explicit error messages:
 
 **Status**: 🔄 DEFERRED for separate session - Large-scale implementation requires careful design
 
-**Why separate**: JoinIR generation involves responsibility boundary decisions (Pattern4 direct vs delegation to Pattern5) and ExitMeta/payload handling. Separating ensures cleaner cause analysis.
+**Why separate**: JoinIR generation involves responsibility boundary decisions and ExitMeta/payload handling. Separating ensures cleaner cause analysis.
 
-**Design questions to resolve first**:
-1. Should return be handled directly in Pattern4 lowerer, or delegated to Pattern5?
-2. How to transport return payload through exit/boundary/ExitMeta (can we reuse ContinueReturn assets)?
+### 🔑 Design Decisions (FIXED for Phase 142 P2 Step 3-B)
+
+#### 1. Return Responsibility Boundary: Pattern5
+
+**Decision**: Return handling → Pattern5 (not Pattern4)
+
+**Rationale**:
+- Pattern4 responsibility: "continue + update rules" only
+- Pattern5 responsibility: "continue + early return" integration
+- Prevents Pattern4 from bloating as parse_string/array/object family expands
+- Aligns with canonicalizer SSOT ("structure is notes, chosen is final lowerer")
+
+**Architecture**:
+```
+Pattern4Continue (recognizer)
+  ↓
+Pattern4Lowerer (continue only)
+  ↓ (has_return? → delegate)
+Pattern5Lowerer (continue + early return)
+```
+
+#### 2. Return Payload Transport: Closed within Pattern5
+
+**Decision**: ExitMeta expansion NOT needed (initially)
+
+**Rationale**:
+- **Judgment criteria**: "Does return need the same exit_line reconnection as break?"
+- **Answer for parse_***: No - "return ends the function" (not carrier reconnect)
+- **Therefore**: Close return payloads within Pattern5 lowerer (no cross-boundary phi)
+
+**Payload Handling**:
+1. Return value lives in a temporary (or direct function return)
+2. No phi merge with continue-side carrier updates
+3. Return path is self-contained within Pattern5
+
+**ContinueReturn Asset Reuse**:
+- ✅ Extract: Value consistency checks + transport logic
+- ❌ Don't reuse: exit_line reconnection machinery (not needed)
+- Reuse only the "payload consistency validation" parts
+
+### 📋 Implementation Checklist for Step 3-B (Next Session)
+
+**Preparation**:
+- [ ] Design Pattern5 entry point (new or enhance existing Pattern5)
+- [ ] Map return payload handling (temporary, no phi merge)
+- [ ] Document ExitMeta usage (confirm unchanged)
+- [ ] Identify ContinueReturn reusable parts (consistency checks)
+
+**Implementation**:
+- [ ] Create `pattern5_continue_return_minimal.rs` lowerer
+- [ ] Add return path handling (closed within Pattern5)
+- [ ] Use existing carrier reconnection from Pattern4 (for continue side)
+- [ ] Test on parse_string minimal fixture
+- [ ] Verify no ExitMeta changes needed
 
 ### SSOT References