feat(joinir): Phase 92 P0-2 - Skeleton to LoopPatternContext (Option A)

SSOT principle: Pass canonicalizer-derived ConditionalStep info to Pattern2 lowerer
without re-detecting from AST.

Changes:
- router.rs: Add skeleton: Option<&'a LoopSkeleton> to LoopPatternContext
- parity_checker.rs: Return (Result, Option<LoopSkeleton>) to reuse skeleton
- routing.rs: Pass skeleton to context when joinir_dev_enabled()
- pattern2_with_break.rs: Detect ConditionalStep in can_lower()

Next: P0-3 implements actual JoinIR generation for ConditionalStep.

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

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

src/mir/builder/control_flow/joinir/patterns/router.rs

@@ -29,6 +29,9 @@ use crate::mir::loop_pattern_detection::{LoopFeatures, LoopPatternKind};
 /// (declared in mod.rs as pub module, import from parent)
 use super::ast_feature_extractor as ast_features;
 
+/// Phase 92 P0-2: Import LoopSkeleton for Option A
+use crate::mir::loop_canonicalizer::LoopSkeleton;
+
 /// Context passed to pattern detect/lower functions
 pub(crate) struct LoopPatternContext<'a> {
     /// Loop condition AST node
@@ -61,6 +64,13 @@ pub(crate) struct LoopPatternContext<'a> {
     /// Phase 200-C: Optional function body AST for capture analysis
     /// None if not available, Some(&[ASTNode]) if function body is accessible
     pub fn_body: Option<&'a [ASTNode]>,
+
+    /// Phase 92 P0-2: Optional LoopSkeleton from canonicalizer
+    /// This provides ConditionalStep information for Pattern2 lowering.
+    /// None if canonicalizer hasn't run yet (backward compatibility).
+    /// SSOT Principle: Avoid re-detecting ConditionalStep in lowering phase.
+    #[allow(dead_code)]
+    pub skeleton: Option<&'a LoopSkeleton>,
 }
 
 impl<'a> LoopPatternContext<'a> {
@@ -71,6 +81,7 @@ impl<'a> LoopPatternContext<'a> {
     /// Phase 193: Feature extraction delegated to ast_feature_extractor module
     /// Phase 131-11: Detects infinite loop condition
     /// Phase 137-6-S1: Use choose_pattern_kind() SSOT entry point
+    /// Phase 92 P0-2: Added skeleton parameter (None for backward compatibility)
     pub(crate) fn new(
         condition: &'a ASTNode,
         body: &'a [ASTNode],
@@ -99,6 +110,7 @@ impl<'a> LoopPatternContext<'a> {
             features,
             pattern_kind,
             fn_body: None, // Phase 200-C: Default to None
+            skeleton: None, // Phase 92 P0-2: Default to None
         }
     }
 
@@ -114,6 +126,13 @@ impl<'a> LoopPatternContext<'a> {
         ctx.fn_body = Some(fn_body);
         ctx
     }
+
+    /// Phase 92 P0-2: Set skeleton (for canonicalizer integration)
+    #[allow(dead_code)]
+    pub(crate) fn with_skeleton(mut self, skeleton: &'a LoopSkeleton) -> Self {
+        self.skeleton = Some(skeleton);
+        self
+    }
 }
 
 /// Phase 193: Feature extraction moved to ast_feature_extractor module