feat(joinir): Phase 192-impl ComplexAddendNormalizer implementation

- New module: complex_addend_normalizer.rs (320 lines, 5 unit tests)
- Transforms `result = result * 10 + f(x)` into temp variable pattern
- Pattern2 preprocessing integration (~40 lines added)
- Zero changes to emission layers (reuses Phase 191 + Phase 190)

Tests:
- Unit tests: 5/5 passing (normalization logic)
- Regression: phase190/191 tests all pass
- Demo: phase192_normalization_demo.hako → 123

Limitation: Full E2E requires Phase 193 (MethodCall in init)

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

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

docs/development/current/main/phase192-complex-addend-design.md

@@ -456,6 +456,145 @@ result = result * 10 + temp_result_addend
 
 ---
 
+---
+
+## Section 9: Implementation Complete (2025-12-09)
+
+### 9.1 Implementation Summary
+
+**Status**: ✅ Phase 192-impl Complete
+
+**Deliverables**:
+1. ✅ `ComplexAddendNormalizer` module implemented (`src/mir/join_ir/lowering/complex_addend_normalizer.rs`)
+2. ✅ 5 unit tests all passing (method call, simple variable, wrong LHS, no multiplication, subtraction)
+3. ✅ Pattern2 integration complete (preprocessing before carrier update analysis)
+4. ✅ Existing tests verified (phase190/191 tests still pass)
+5. ✅ Documentation updated
+
+### 9.2 Actual Implementation
+
+**File**: `src/mir/join_ir/lowering/complex_addend_normalizer.rs`
+
+**API**:
+```rust
+pub enum NormalizationResult {
+    Unchanged,
+    Normalized { temp_def: ASTNode, new_assign: ASTNode, temp_name: String },
+}
+
+impl ComplexAddendNormalizer {
+    pub fn normalize_assign(assign: &ASTNode) -> NormalizationResult;
+}
+```
+
+**Integration Point** (Pattern2 - line 243-279):
+```rust
+// Phase 192: Normalize complex addend patterns in loop body
+let mut normalized_body = Vec::new();
+let mut has_normalization = false;
+
+for node in _body {
+    match ComplexAddendNormalizer::normalize_assign(node) {
+        NormalizationResult::Normalized { temp_def, new_assign, temp_name } => {
+            normalized_body.push(temp_def);      // local temp = <complex_expr>
+            normalized_body.push(new_assign);    // lhs = lhs * base + temp
+            has_normalization = true;
+        }
+        NormalizationResult::Unchanged => {
+            normalized_body.push(node.clone());
+        }
+    }
+}
+
+let analysis_body = if has_normalization { &normalized_body } else { _body };
+// Pass analysis_body to LoopUpdateAnalyzer and lower_loop_with_break_minimal
+```
+
+### 9.3 AST Transformation Example
+
+**Before**:
+```nyash
+result = result * 10 + digits.indexOf(ch)
+```
+
+**After** (Normalized AST):
+```nyash
+local temp_result_addend = digits.indexOf(ch)
+result = result * 10 + temp_result_addend
+```
+
+**AST Structure**:
+```
+[
+  Local { variables: ["temp_result_addend"], initial_values: [MethodCall(...)] },
+  Assignment { target: "result", value: BinOp(Add, BinOp(Mul, "result", 10), "temp_result_addend") }
+]
+```
+
+### 9.4 Test Results
+
+**Unit Tests** (5/5 passing):
+- ✅ `test_normalize_complex_addend_method_call` - Core normalization pattern
+- ✅ `test_normalize_simple_variable_unchanged` - No-op for simple patterns
+- ✅ `test_normalize_wrong_lhs_unchanged` - Reject invalid patterns
+- ✅ `test_normalize_no_multiplication_unchanged` - Reject non-accumulation patterns
+- ✅ `test_normalize_subtraction_complex_addend` - Subtraction variant
+
+**Integration Tests** (regression verified):
+- ✅ `phase190_atoi_impl.hako` → 12 (no regression)
+- ✅ `phase190_parse_number_impl.hako` → 123 (no regression)
+- ✅ `phase191_body_local_atoi.hako` → 123 (no regression)
+- ✅ `phase192_normalization_demo.hako` → 123 (new demo test)
+
+### 9.5 Current Limitations (Phase 193+ Work)
+
+**Limitation**: Full E2E flow with MethodCall in temp variables requires extending `LoopBodyLocalInitLowerer` (Phase 186).
+
+**Current Behavior**:
+```nyash
+local temp = digits.indexOf(ch)  // ❌ Phase 186 error: "Unsupported init expression: method call"
+```
+
+**Phase 186 Scope**: Only supports int/arithmetic operations (`+`, `-`, `*`, `/`, constants, variables)
+
+**Future Work** (Phase 193+):
+- Extend `LoopBodyLocalInitLowerer::lower_init_expr()` to handle:
+  - `ASTNode::MethodCall` (e.g., `digits.indexOf(ch)`)
+  - `ASTNode::Call` (e.g., `parseInt(s)`)
+- Add emission logic for method call results in JoinIR
+- Add UpdateEnv resolution for method call temps
+
+**Workaround**: For now, complex addend normalization works at the AST level, but lowering requires manual temp extraction outside the loop.
+
+### 9.6 Design Principles Validated
+
+✅ **箱化 (Box-First)**:
+- ComplexAddendNormalizer is a pure AST transformer (single responsibility)
+- No emission logic mixed in (delegation to existing Phase 191/190 infrastructure)
+
+✅ **Fail-Fast**:
+- Unsupported patterns return `NormalizationResult::Unchanged`
+- Phase 186 limitation explicitly documented
+
+✅ **Reusability**:
+- Normalizer works with any BinaryOp pattern (Add/Subtract)
+- Integration point is clean (10 lines in Pattern2)
+
+✅ **Minimal Changes**:
+- Zero changes to emission layers (CarrierUpdateEmitter, LoopBodyLocalInitLowerer)
+- Only preprocessing added to Pattern2 (before carrier analysis)
+
+### 9.7 Trace Output
+
+When running a test with complex addend pattern:
+```
+[pattern2/phase192] Normalized complex addend: temp='temp_result_addend' inserted before update
+[cf_loop/pattern2] Phase 176-3: Analyzed 1 carrier updates
+```
+
+---
+
 ## Revision History
 
 - **2025-12-09**: Initial design document (Section 1-8)
+- **2025-12-09**: Implementation complete (Section 9)