feat(joinir): Phase 220-D loop condition variable support complete

Modified extract_loop_condition() to use ConditionEnv for variable lookup:
- Now returns ValueId instead of i64 for loop limit
- Uses lower_value_expression() for both literals and variables
- Integrated ConditionEnvBuilder in Pattern 3 if-sum path

This enables realistic loop patterns like `loop(i < len)` in if-sum.

🤖 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/pattern3_with_if_phi.rs

@@ -112,11 +112,31 @@ impl MirBuilder {
             "[cf_loop/pattern3] if-sum pattern detected but no if statement found".to_string()
         })?;
 
-        // Call AST-based if-sum lowerer
+        // Phase 220-D: Build ConditionEnv for variable resolution
+        use super::condition_env_builder::ConditionEnvBuilder;
+        let loop_var_name = ctx.loop_var_name.clone();
+        let loop_var_id = ctx.loop_var_id;
+
+        let (cond_env, condition_bindings, _loop_var_join_id) =
+            ConditionEnvBuilder::build_for_break_condition_v2(
+                condition,
+                &loop_var_name,
+                &self.variable_map,
+                loop_var_id,
+                &mut join_value_space,
+            )?;
+
+        eprintln!("[pattern3/if-sum] Phase 220-D: ConditionEnv has {} bindings", condition_bindings.len());
+        for binding in &condition_bindings {
+            eprintln!("  '{}': HOST {:?} → JoinIR {:?}", binding.name, binding.host_value, binding.join_value);
+        }
+
+        // Call AST-based if-sum lowerer with ConditionEnv
         let (join_module, fragment_meta) = lower_if_sum_pattern(
             condition,
             if_stmt,
             body,
+            &cond_env,
             &mut join_value_space,
         )?;
 
@@ -174,8 +194,10 @@ impl MirBuilder {
         );
 
         // Phase 215-2: Pass expr_result to boundary
+        // Phase 220-D: Pass condition_bindings for variable remapping
         let mut boundary_builder = JoinInlineBoundaryBuilder::new()
             .with_inputs(join_inputs, host_inputs)
+            .with_condition_bindings(condition_bindings)  // Phase 220-D: Map condition-only vars
             .with_exit_bindings(exit_bindings)
             .with_loop_var_name(Some(ctx.loop_var_name.clone()));