refactor(joinir): Phase 242-EX-A - Delete legacy Pattern3 lowerer

Remove hardcoded Pattern3 PoC implementation (loop_with_if_phi_minimal.rs)
and enhance if-sum mode to handle complex conditions like `i % 2 == 1`.

Key changes:
- condition_pattern.rs: Accept BinaryOp in comparison operands (+58 lines)
- loop_with_if_phi_if_sum.rs: Dynamic complex condition lowering (+147 lines)
- pattern3_with_if_phi.rs: Remove lower_pattern3_legacy() (-130 lines)
- loop_with_if_phi_minimal.rs: Delete entire file (-437 lines)
- loop_patterns/with_if_phi.rs: Update stub (-45 lines)
- mod.rs: Remove module reference (-4 lines)

Net reduction: -664 lines of hardcoded PoC code

Test results: 909/909 PASS (legacy mode completely removed)

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

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

src/mir/join_ir/lowering/loop_patterns/with_if_phi.rs

@@ -83,46 +83,9 @@ pub fn lower_loop_with_conditional_phi_to_joinir(
     _loop_form: &LoopForm,
     _lowerer: &mut LoopToJoinLowerer,
 ) -> Option<JoinInst> {
-    // Phase 188-Impl-3: Delegate to minimal lowerer
-    // TODO: Extract LoopScopeShape from loop_form for generic implementation
-    use crate::mir::join_ir::lowering::join_value_space::JoinValueSpace;
-    use crate::mir::join_ir::lowering::loop_scope_shape::LoopScopeShape;
-    use crate::mir::join_ir::lowering::loop_with_if_phi_minimal::lower_loop_with_if_phi_pattern;
-    use crate::mir::BasicBlockId;
-    use std::collections::{BTreeMap, BTreeSet};
-
-    // For now, use a placeholder LoopScopeShape
-    // TODO: Build actual LoopScopeShape from loop_form
-    let placeholder_scope = LoopScopeShape {
-        header: BasicBlockId(0),
-        body: BasicBlockId(0),
-        latch: BasicBlockId(0),
-        exit: BasicBlockId(0),
-        pinned: BTreeSet::new(),
-        carriers: BTreeSet::new(),
-        body_locals: BTreeSet::new(),
-        exit_live: BTreeSet::new(),
-        progress_carrier: None,
-        variable_definitions: BTreeMap::new(),
-    };
-
-    // Phase 202-B: Create JoinValueSpace for unified ValueId allocation
-    let mut join_value_space = JoinValueSpace::new();
-
-    // Generate JoinIR module
-    // Phase 213: Updated to handle Result<(JoinModule, JoinFragmentMeta), String>
-    let _result = lower_loop_with_if_phi_pattern(placeholder_scope, &mut join_value_space).ok()?;
-
-    // Phase 188-Impl-3: Pattern 3 is now integrated via the router
-    // This function delegates to loop_with_if_phi_minimal which generates JoinModule
-    //
-    // TODO: Either:
-    // 1. Remove this function and rely only on router integration, OR
-    // 2. Implement JoinModule → JoinInst conversion here (future phase)
-
-    eprintln!("[loop_patterns] Pattern 3: Lowering delegated to loop_with_if_phi_minimal");
-
-    // Temporary: Return None to trigger fallback
-    // Pattern 3 currently works via router which calls minimal lowerer directly
+    // Phase 242-EX-A: Legacy stub removed
+    // Pattern 3 is now fully handled via router → pattern3_with_if_phi.rs → loop_with_if_phi_if_sum.rs
+    // This stub function is unused and kept only for API compatibility
+    eprintln!("[loop_patterns] Pattern 3: Stub - routing via pattern3_with_if_phi.rs");
     None
 }