refactor(joinir): L-1.3 - Rename minimal helpers to Case-A helpers

LoopToJoinLowerer API cleanup:

1. Rename methods to reflect their purpose as Case-A helpers:
   - lower_minimal_skip_ws_case_a → lower_case_a_for_skip_ws
   - lower_minimal_trim_case_a → lower_case_a_for_trim
   - lower_minimal_append_defs_case_a → lower_case_a_for_append_defs
   - lower_minimal_stage1_case_a → lower_case_a_for_stage1_resolver

2. Update comments to clarify these are thin wrappers over `lower()`
   - "Case-A 汎用 lowerer の薄いラッパー"
   - Actual logic is centralized in `lower` method

3. Update all 4 call sites:
   - skip_ws.rs
   - funcscanner_trim.rs
   - funcscanner_append_defs.rs
   - stage1_using_resolver.rs

Test results: standalone (2/2), JSON snapshot (6/6) PASS

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

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

src/mir/join_ir/lowering/funcscanner_append_defs.rs

@@ -368,7 +368,7 @@ fn lower_from_mir(module: &crate::mir::MirModule) -> Option<JoinModule> {
                 "[joinir/funcscanner_append_defs/generic-hook] detected simple Case A loop (LoopToJoinLowerer)"
             );
             let lowerer = LoopToJoinLowerer::new();
-            if let Some(jm) = lowerer.lower_minimal_append_defs_case_a(target_func, &loop_form) {
+            if let Some(jm) = lowerer.lower_case_a_for_append_defs(target_func, &loop_form) {
                 eprintln!(
                     "[joinir/funcscanner_append_defs/generic-hook] LoopToJoinLowerer produced JoinIR, returning early"
                 );

src/mir/join_ir/lowering/funcscanner_trim.rs

@@ -635,7 +635,7 @@ fn lower_trim_from_mir(module: &crate::mir::MirModule) -> Option<JoinModule> {
                 "[joinir/trim/generic-hook] simple Case A loop detected (LoopToJoinLowerer)"
             );
             let lowerer = LoopToJoinLowerer::new();
-            if let Some(jm) = lowerer.lower_minimal_trim_case_a(target_func, &loop_form) {
+            if let Some(jm) = lowerer.lower_case_a_for_trim(target_func, &loop_form) {
                 eprintln!("[joinir/trim/generic-hook] LoopToJoinLowerer produced JoinIR, returning early");
                 return Some(jm);
             }

src/mir/join_ir/lowering/loop_to_join.rs

@@ -297,14 +297,12 @@ impl LoopToJoinLowerer {
     }
 
     // ========================================
-    // Convenience methods for specific patterns
+    // Case-A helpers for specific function patterns
     // ========================================
 
-    /// Main.skip/1 専用の lowering
-    ///
-    /// Phase 31 Step 1 の検証用メソッド。
-    /// 既存の `skip_ws.rs` からの移行確認に使用。
-    pub fn lower_minimal_skip_ws_case_a(
+    /// Case-A 汎用 lowerer の「Main.skip/1 用」薄いラッパー。
+    /// 実際のロジックは `lower` に集約されている。
+    pub fn lower_case_a_for_skip_ws(
         &self,
         func: &MirFunction,
         loop_form: &LoopForm,
@@ -312,8 +310,9 @@ impl LoopToJoinLowerer {
         self.lower(func, loop_form, Some("Main.skip/1"))
     }
 
-    /// FuncScannerBox.trim/1 専用の lowering
-    pub fn lower_minimal_trim_case_a(
+    /// Case-A 汎用 lowerer の「FuncScannerBox.trim/1 用」薄いラッパー。
+    /// 実際のロジックは `lower` に集約されている。
+    pub fn lower_case_a_for_trim(
         &self,
         func: &MirFunction,
         loop_form: &LoopForm,
@@ -321,8 +320,9 @@ impl LoopToJoinLowerer {
         self.lower(func, loop_form, Some("FuncScannerBox.trim/1"))
     }
 
-    /// FuncScannerBox.append_defs/2 専用の lowering
-    pub fn lower_minimal_append_defs_case_a(
+    /// Case-A 汎用 lowerer の「FuncScannerBox.append_defs/2 用」薄いラッパー。
+    /// 実際のロジックは `lower` に集約されている。
+    pub fn lower_case_a_for_append_defs(
         &self,
         func: &MirFunction,
         loop_form: &LoopForm,
@@ -330,8 +330,9 @@ impl LoopToJoinLowerer {
         self.lower(func, loop_form, Some("FuncScannerBox.append_defs/2"))
     }
 
-    /// Stage1UsingResolverBox.resolve_for_source/5 専用の lowering
-    pub fn lower_minimal_stage1_case_a(
+    /// Case-A 汎用 lowerer の「Stage1UsingResolverBox.resolve_for_source/5 用」薄いラッパー。
+    /// 実際のロジックは `lower` に集約されている。
+    pub fn lower_case_a_for_stage1_resolver(
         &self,
         func: &MirFunction,
         loop_form: &LoopForm,

src/mir/join_ir/lowering/skip_ws.rs

@@ -382,5 +382,5 @@ fn try_lower_skip_ws_generic_case_a(module: &crate::mir::MirModule) -> Option<Jo
 
     // Phase 31: LoopToJoinLowerer 経由で JoinModule 生成
     let lowerer = LoopToJoinLowerer::new();
-    lowerer.lower_minimal_skip_ws_case_a(target_func, &loop_form)
+    lowerer.lower_case_a_for_skip_ws(target_func, &loop_form)
 }

src/mir/join_ir/lowering/stage1_using_resolver.rs

@@ -369,7 +369,7 @@ fn lower_from_mir(module: &crate::mir::MirModule) -> Option<JoinModule> {
             let params_len = target_func.params.len();
             if params_len == 5 {
                 let lowerer = LoopToJoinLowerer::new();
-                if let Some(jm) = lowerer.lower_minimal_stage1_case_a(target_func, &loop_form) {
+                if let Some(jm) = lowerer.lower_case_a_for_stage1_resolver(target_func, &loop_form) {
                     eprintln!(
                         "[joinir/stage1_using_resolver/generic-hook] LoopToJoinLowerer produced JoinIR, returning early"
                     );