docs(normalization): Update README for Phase 142 P0

- Document statement-level normalization unit change
- Add Phase 142 P0 section to Pattern Detection
- Mark Phase 132-135 patterns as LEGACY
- Update suffix_router description
- Clarify LoopWithPost deprecation status

Phase 142 P0: Normalization unit changed from "block suffix" to "statement"

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

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

src/mir/builder/control_flow/normalization/README.md

@@ -28,7 +28,10 @@ Consolidate the two separate entry points for Normalized shadow processing into
 
 **Two callers, one SSOT decision**:
 - `routing.rs::try_normalized_shadow()`: Loop-only patterns (Phase 131)
-- `suffix_router_box::try_lower_loop_suffix()`: Loop + post patterns (Phase 132-133)
+- `suffix_router_box::try_lower_loop_suffix()`: Loop patterns at block suffix (Phase 131+)
+  - **Phase 142 P0**: Now accepts both LoopOnly and LoopWithPost (deprecated)
+  - Statement-level normalization: only the loop is normalized (consumed=1)
+  - Subsequent statements (return, assignments) handled by normal MIR lowering
 - Both call `NormalizationPlanBox::plan_block_suffix()` for detection
 
 ### Box Responsibilities
@@ -54,8 +57,9 @@ pub struct NormalizationPlan {
 }
 
 pub enum PlanKind {
-    LoopOnly,                     // Phase 131: loop(true) { ... break } alone
-    LoopWithPost {                // Phase 132-133: loop + post assigns + return
+    LoopOnly,                     // Phase 131+142 P0: loop(true) { ... break } alone
+    #[deprecated]                 // Phase 142 P0: DEPRECATED - statement-level normalization
+    LoopWithPost {                // Phase 132-133 (legacy): loop + post assigns + return
         post_assign_count: usize,
     },
 }
@@ -87,7 +91,7 @@ pub enum PlanKind {
 
 ---
 
-## Pattern Detection (Phase 131-135)
+## Pattern Detection (Phase 131-135, updated Phase 142 P0)
 
 ### Phase 131: Loop-Only
 - Pattern: `loop(true) { ... break }` (single statement, no return)
@@ -107,13 +111,24 @@ pub enum PlanKind {
 - Kind: `PlanKind::LoopWithPost { post_assign_count: N }`
 - Example: `loop(true) { x = 1; break }; x = x + 2; x = x + 3; return x`
 
-### Phase 135: Loop + Return (Zero Post Assigns) **NEW**
+### Phase 135: Loop + Return (Zero Post Assigns) **LEGACY**
 - Pattern: `loop(true) { ... break }; return <expr>` (0 post-loop assignments)
 - Consumed: 2 statements (loop, return)
 - Kind: `PlanKind::LoopWithPost { post_assign_count: 0 }`
 - Example: `loop(true) { x = 1; break }; return x`
 - **Improvement**: Unifies Phase 131 and Phase 132-133 patterns under `LoopWithPost` enum
 - **Compatibility**: Phase 131 (loop-only, no return) remains as `PlanKind::LoopOnly`
+- **Status**: Deprecated in Phase 142 P0 (see below)
+
+### Phase 142 P0: Statement-Level Normalization **CURRENT**
+- **Change**: Normalization unit changed from "block suffix" to "statement (loop only)"
+- **Pattern**: `loop(true) { ... break }` - always returns `LoopOnly`, regardless of subsequent statements
+- **Consumed**: Always 1 statement (the loop itself)
+- **Kind**: `PlanKind::LoopOnly`
+- **Subsequent statements**: Handled by normal MIR lowering (not normalized)
+- **Example**: `loop(true) { break }; return s.length()` → loop normalized (consumed=1), return handled normally
+- **Impact**: Prevents pattern explosion by separating loop normalization from post-loop statements
+- **Deprecated**: `LoopWithPost` variant no longer created, kept for backward compatibility only
 
 ---