refactor(joinir): Unify Pattern 1 with PatternPipelineContext

- Reduced preprocessing from 61 lines to ~30 lines (51% reduction)
- Total file size: 139 → 118 lines (15% reduction)
- Uses build_pattern_context() for unified initialization
- All tests passing (loop_min_while.hako verified)

src/mir/builder/control_flow/joinir/patterns/pattern1_minimal.rs

@@ -27,62 +27,41 @@ pub fn lower(
 }
 
 impl MirBuilder {
-    /// Phase 188-Impl-1-F: Pattern 1 (Simple While Loop) minimal lowerer
+    /// Phase 179-B: Pattern 1 (Simple While Loop) minimal lowerer
     ///
-    /// This bypasses the LoopFrontendBinding JSON path and directly calls
-    /// the Pattern 1 minimal lowerer for apps/tests/loop_min_while.hako
+    /// **Refactored**: Now uses PatternPipelineContext for unified preprocessing
     ///
-    /// # Phase 188-Impl-2: Host Variable Integration
-    ///
-    /// Extracts the loop variable from the host function (e.g., `i` from `i < 3`)
-    /// and creates a JoinInlineBoundary for mapping between host and JoinIR ValueIds.
-    ///
-    /// # Pipeline
-    /// 1. Extract loop variable name from condition
-    /// 2. Look up ValueId in host variable_map
-    /// 3. Call simple_while_minimal::lower_simple_while_minimal() → JoinModule
-    /// 4. convert_join_module_to_mir_with_meta() → MirModule
-    /// 5. Merge MIR blocks into current_function
+    /// # Pipeline (Phase 179-B)
+    /// 1. Build preprocessing context → PatternPipelineContext
+    /// 2. Call JoinIR lowerer → JoinModule
+    /// 3. Create boundary from context → JoinInlineBoundary
+    /// 4. Merge MIR blocks → JoinIRConversionPipeline
     pub(in crate::mir::builder) fn cf_loop_pattern1_minimal(
         &mut self,
         condition: &ASTNode,
-        _body: &[ASTNode],
+        body: &[ASTNode],
         _func_name: &str,
         debug: bool,
     ) -> Result<Option<ValueId>, String> {
         use crate::mir::join_ir::lowering::simple_while_minimal::lower_simple_while_minimal;
-        use crate::mir::BasicBlockId;
-        use std::collections::BTreeSet;
 
         // Phase 195: Use unified trace
         trace::trace().debug("pattern1", "Calling Pattern 1 minimal lowerer");
 
-        // Phase 33-22: Use CommonPatternInitializer for loop variable extraction
-        use super::common_init::CommonPatternInitializer;
-        let (loop_var_name, loop_var_id, _carrier_info) =
-            CommonPatternInitializer::initialize_pattern(
+        // Phase 179-B: Use PatternPipelineContext for unified preprocessing
+        use super::pattern_pipeline::{build_pattern_context, PatternVariant};
+        let ctx = build_pattern_context(
             self,
             condition,
-                &self.variable_map,
-                None, // No carrier exclusions for Pattern 1
+            body,
+            PatternVariant::Pattern1,
         )?;
 
         // Phase 195: Use unified trace
         trace::trace().varmap("pattern1_start", &self.variable_map);
 
-        // Phase 171-172: Use LoopScopeShapeBuilder for unified initialization (Issue 4)
-        // Pattern 1 lowerer ignores the scope anyway, so this is just a placeholder
-        use super::loop_scope_shape_builder::LoopScopeShapeBuilder;
-        let scope = LoopScopeShapeBuilder::empty_body_locals(
-            BasicBlockId(0),
-            BasicBlockId(0),
-            BasicBlockId(0),
-            BasicBlockId(0),
-            BTreeSet::new(),
-        );
-
-        // Call Pattern 1 lowerer
-        let join_module = match lower_simple_while_minimal(scope) {
+        // Call Pattern 1 lowerer with preprocessed scope
+        let join_module = match lower_simple_while_minimal(ctx.loop_scope) {
             Some(module) => module,
             None => {
                 // Phase 195: Use unified trace
@@ -91,16 +70,16 @@ impl MirBuilder {
             }
         };
 
-        // Phase 33-22: Create boundary for JoinIR conversion
+        // Phase 179-B: Create boundary from context
         // Phase 201: Use JoinInlineBoundaryBuilder for clean construction
         // Canonical Builder pattern - see docs/development/current/main/joinir-boundary-builder-pattern.md
         use crate::mir::join_ir::lowering::JoinInlineBoundaryBuilder;
         let boundary = JoinInlineBoundaryBuilder::new()
             .with_inputs(
                 vec![ValueId(0)],      // JoinIR's main() parameter (loop variable)
-                vec![loop_var_id],     // Host's loop variable
+                vec![ctx.loop_var_id], // Host's loop variable
             )
-            .with_loop_var_name(Some(loop_var_name.clone()))  // Phase 33-16: Enable header PHI generation for SSA correctness
+            .with_loop_var_name(Some(ctx.loop_var_name.clone()))  // Phase 33-16: Enable header PHI generation for SSA correctness
             .build();
 
         // Phase 33-22: Use JoinIRConversionPipeline for unified conversion flow