feat(plan): Phase 282 P5 - Pattern3 ExtractionBased Migration & Classification

- Pattern3 extraction logic separated to extractors/pattern3.rs
- ExtractionBased strategy: pure functions, Fail-Fast, SSOT
- Pattern classification restored (AST-based pattern detection)
- Pattern1 extractor migrated (extractors/pattern1.rs)
- Documentation: phase-282 README updated, joinir-architecture updated

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

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

docs/development/current/main/joinir-architecture-overview.md

@@ -163,7 +163,7 @@ Pattern numbers (1-9+) became architectural decision points:
 - `seq(a, b)`: Sequential composition (Normal wiring)
 - `if_(header, cond, t, e, join)`: Conditional composition (Branch wiring)
 - `loop_(loop_id, header, after, body)`: Loop composition (Break/Continue wiring)
-- `cleanup(body, cleanup)`: Cleanup composition (planned, Phase 280+)
+- `cleanup(main, cleanup_frag, normal_target, ret_target)`: Cleanup composition (Normal/Return wiring; Phase 281)
 
 **Reference**: `docs/development/current/main/design/edgecfg-fragments.md` (Active SSOT)
 
@@ -183,36 +183,36 @@ Both routes converge on the same Frag composition SSOT:
 - Plan route: Handles complex scan patterns (Pattern6/7) via DomainPlan → CorePlan → Frag
 - Both routes use same Frag composition API for CFG lowering (no duplication)
 
-### Pattern Absorption Status (Phase 280)
+### Pattern Absorption Status (Phase 281)
 
 | Pattern | Structure | Status | Absorption Target |
 |---------|-----------|--------|-------------------|
-| **Pattern6** | ScanWithInit (forward scan) | Plan-based (Phase 273) | **Phase 280 C: Frag refactor target** |
-| **Pattern7** | SplitScan (conditional split) | Plan-based (Phase 273) | **Phase 280 C: Frag refactor target** |
-| Pattern8 | BoolPredicateScan (is_integer) | JoinIR-based | Phase 281+ (migration planned) |
+| **Pattern6** | ScanWithInit (early-exit) | ✅ compose-based (Phase 281) | absorbed (hand-roll removed) |
+| **Pattern7** | SplitScan (then/else join) | ✅ compose-based (Phase 281) | absorbed (hand-roll removed) |
+| Pattern8 | BoolPredicateScan (is_integer) | JoinIR-based | Phase 283+ (migration planned) |
 | Pattern9 | AccumConstLoop (bridge) | JoinIR-based (Phase 271) | 撤去条件 defined (minimal loop SSOT) |
 | Pattern1-5 | Legacy (SimpleWhile, Break, IfPhi, Continue, InfiniteEarlyExit) | JoinIR-based | Test/error stubs (not absorbed) |
 
-**Phase 280 Focus**: Pattern6/7 preparation (documentation of hand-rolled locations, defer refactor to Phase 281)
+**Phase 281 Result**: Pattern6/7 absorbed (compose SSOT), hand-rolled Frag eliminated
 
 **Absorption criteria** (Pattern6/7 → Frag composition):
 1. Hand-rolled Frag construction identified (function name + 識別コメント)
 2. TODO comments documenting future compose_* migration path
-3. Behavior-preserving refactor deferred to Phase 281 (Phase 280 = SSOT positioning only)
+3. Behavior-preserving refactor completed in Phase 281
 
 ### Absorption Timeline
 
-**Phase 280 (Current)**: SSOT positioning + 導線固定
+**Phase 280 (Complete)**: SSOT positioning + 導線固定
 - A: Documentation (edgecfg-fragments.md → Active SSOT)
 - B: API solidification (compose.rs contract verification)
 - C: Pattern preparation (Pattern6/7 hand-rolled locations documented)
 - **Goal**: Establish Frag composition as THE absorption destination
 - **Non-Goal**: Full Pattern6/7 migration (deferred to Phase 281)
 
-**Phase 281 (Planned)**: Full Pattern6/7 absorption
-- Replace hand-rolled Frag construction with compose_* calls
-- Behavior-preserving verification (smoke tests)
-- Goal: Pattern6/7 use compose::if_/loop_ exclusively
+**Phase 281 (Complete)**: Full Pattern6/7 absorption
+- Pattern7: body cond_match → `compose::if_()`
+- Pattern6: early-exit → `compose::cleanup()`（Normal/Return wiring）
+- Behavior-preserving verification (VM/LLVM smokes)
 
 **Phase 282 (Planned)**: Router shrinkage
 - Pattern numbers → test labels only