fix(normalization): Tighten loop(true) gate to prevent loop(i<n) mismatch

Problem:
- Phase 97 LLVM EXE tests (next_non_ws, json_loader_escape) were failing
- NormalizationPlan accepted loop(i < n) but couldn't lower it
- Execute stage returned hard error instead of fallback

Root Cause:
- Plan stage only checked `ASTNode::Loop`, not condition
- loop(i < n) got Plan → Execute tried to normalize → error
- Should: loop(i < n) returns Ok(None) → fallback to Pattern2

Fix:
- Tighten gate in plan_box.rs (lines 50-71)
- Only accept loop(true) - literal Bool true
- loop(i < n) now returns Ok(None) → clean fallback

Added:
- Test: test_plan_block_suffix_no_match_loop_not_true()
- Verifies loop(i < n) returns None (not Plan)

Verification:
- Phase 97 next_non_ws LLVM EXE: PASS
- Phase 97 json_loader_escape LLVM EXE: PASS
- Phase 131/135/136/137 regression: all PASS

🤖 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/plan_box.rs

@@ -12,7 +12,7 @@
 //! - Returns Ok(None): Not a normalized pattern, use legacy fallback
 //! - Returns Err(_): Internal error (malformed AST)
 
-use crate::ast::ASTNode;
+use crate::ast::{ASTNode, LiteralValue};
 use crate::mir::builder::MirBuilder;
 use super::plan::{NormalizationPlan, PlanKind};
 
@@ -47,9 +47,26 @@ impl NormalizationPlanBox {
             return Ok(None);
         }
 
-        // First statement must be a loop
+        // First statement must be a loop with condition `true`
-        let is_loop = matches!(&remaining[0], ASTNode::Loop { .. });
+        // Phase 131-136 ONLY support loop(true), not loop(i < n) etc.
-        if !is_loop {
+        let is_loop_true = match &remaining[0] {
+            ASTNode::Loop { condition, .. } => {
+                // Only accept loop(true) - literal Bool true
+                matches!(
+                    condition.as_ref(),
+                    ASTNode::Literal { value: LiteralValue::Bool(true), .. }
+                )
+            }
+            _ => false,
+        };
+        if !is_loop_true {
+            if debug {
+                trace.routing(
+                    "normalization/plan",
+                    func_name,
+                    "First statement is not loop(true), returning None (not a normalized pattern)",
+                );
+            }
             return Ok(None);
         }
 
@@ -363,4 +380,50 @@ mod tests {
         assert_eq!(plan.consumed, 2); // loop + return
         assert_eq!(plan.kind, PlanKind::LoopWithPost { post_assign_count: 0 });
     }
+
+    #[test]
+    fn test_plan_block_suffix_no_match_loop_not_true() {
+        use crate::mir::builder::MirBuilder;
+
+        // Phase 97 regression test: loop(i < n) should NOT match
+        // Normalized shadow only supports loop(true)
+        let loop_conditional = ASTNode::Loop {
+            condition: Box::new(ASTNode::BinaryOp {
+                left: Box::new(ASTNode::Variable {
+                    name: "i".to_string(),
+                    span: make_span(),
+                }),
+                operator: BinaryOperator::Less,
+                right: Box::new(ASTNode::Variable {
+                    name: "n".to_string(),
+                    span: make_span(),
+                }),
+                span: make_span(),
+            }),
+            body: vec![
+                ASTNode::Assignment {
+                    target: Box::new(ASTNode::Variable {
+                        name: "x".to_string(),
+                        span: make_span(),
+                    }),
+                    value: Box::new(ASTNode::Literal {
+                        value: LiteralValue::Integer(1),
+                        span: make_span(),
+                    }),
+                    span: make_span(),
+                },
+                ASTNode::Break { span: make_span() },
+            ],
+            span: make_span(),
+        };
+
+        let remaining = vec![loop_conditional, make_return("x")];
+
+        let builder = MirBuilder::new();
+        let plan = NormalizationPlanBox::plan_block_suffix(&builder, &remaining, "test", false)
+            .expect("Should not error");
+
+        // loop(i < n) is NOT supported by Normalized - should return None
+        assert!(plan.is_none(), "loop(i < n) should NOT match Normalized pattern");
+    }
 }