diff --git a/src/mir/join_ir/lowering/generic_case_a.rs b/src/mir/join_ir/lowering/generic_case_a.rs
index d430ef98..74febca6 100644
--- a/src/mir/join_ir/lowering/generic_case_a.rs
+++ b/src/mir/join_ir/lowering/generic_case_a.rs
@@ -6,10 +6,9 @@
 //! - pinned/carrier/exit は LoopVarClassBox / LoopExitLivenessBox から渡された前提で扱う
 //! - 解析に失敗したら必ず None を返し、呼び元にフォールバックさせる
 
-use std::collections::{BTreeMap, BTreeSet};
+use std::collections::BTreeMap;
 
-use crate::mir::join_ir::lowering::exit_args_resolver::resolve_exit_args;
-use crate::mir::join_ir::lowering::loop_form_intake::{intake_loop_form, LoopFormIntake};
+use crate::mir::join_ir::lowering::loop_scope_shape::CaseAContext;
 use crate::mir::join_ir::lowering::value_id_ranges;
 use crate::mir::join_ir::lowering::value_id_ranges::skip_ws as vid;
 use crate::mir::join_ir::lowering::value_id_ranges::stage1_using_resolver as stage1_vid;
@@ -33,13 +32,8 @@ pub fn lower_case_a_loop_to_joinir_for_minimal_skip_ws(
     query: &impl MirQuery,
     mir_func: &MirFunction,
 ) -> Option<JoinModule> {
-    // 1) LoopForm が Case A っぽいか最低限チェック（header→body/exit、latch→header）
-    if loop_form.header == loop_form.exit {
-        eprintln!("[joinir/generic_case_a] loop_form malformed (header == exit), fallback");
-        return None;
-    }
+    // 追加の latch チェック（skip_ws 固有）
     if loop_form.latch != loop_form.body && loop_form.latch != loop_form.header {
-        // minimal_skip_ws では latch==body or header 想定。違えばフォールバック。
         eprintln!(
             "[joinir/generic_case_a] unexpected latch {:?} (body={:?}, header={:?}), fallback",
             loop_form.latch, loop_form.body, loop_form.header
@@ -47,53 +41,25 @@ pub fn lower_case_a_loop_to_joinir_for_minimal_skip_ws(
         return None;
     }
 
-    // 2) MIR から pinned/carrier/exit 情報を抽出する
-    let LoopFormIntake {
-        pinned_ordered: ordered_pinned,
-        carrier_ordered: ordered_carriers,
-        name_to_header_id: _name_to_id,
-        header_snapshot: header_vals_mir,
-        exit_snapshots,
-        exit_preds: _exit_preds,
-    } = intake_loop_form(loop_form, var_classes, query, mir_func)?;
+    // CaseAContext で共通ロジックを実行
+    let ctx = CaseAContext::new(
+        loop_form,
+        var_classes,
+        exit_live,
+        query,
+        mir_func,
+        "skip_ws",
+        |offset| vid::loop_step(offset),
+    )?;
 
-    // JoinIR 用の ValueId を範囲から割り当て（名前→ID マップ）
-    let mut name_to_loop_id: BTreeMap<String, ValueId> = BTreeMap::new();
-    let mut offset = 0;
-    for name in &ordered_pinned {
-        name_to_loop_id.insert(name.clone(), vid::loop_step(offset));
-        offset += 1;
-    }
-    for name in &ordered_carriers {
-        name_to_loop_id.insert(name.clone(), vid::loop_step(offset));
-        offset += 1;
-    }
+    // JoinModule を手書き skip_ws と同じ形で構築（ValueId 範囲も揃える）
+    let string_key = ctx.pinned_name_or_first(0)?;
+    let len_key = ctx.pinned_name_or_first(1).unwrap_or_else(|| string_key.clone());
+    let index_key = ctx.carrier_name_or_first(0)?;
 
-    let pinned_ids: Vec<ValueId> = ordered_pinned
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-    let carrier_ids: Vec<ValueId> = ordered_carriers
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-
-    // Exit live 集合（LoopExitLivenessBox を利用）
-    let exit_live_set: BTreeSet<String> =
-        exit_live.compute_live_at_exit(query, loop_form.exit, &header_vals_mir, &exit_snapshots);
-    let exit_args = resolve_exit_args(&exit_live_set, &name_to_loop_id, &ordered_carriers)?;
-
-    // 3) JoinModule を手書き skip_ws と同じ形で構築（ValueId 範囲も揃える）
-    let string_key = ordered_pinned.get(0).cloned()?;
-    let len_key = ordered_pinned
-        .get(1)
-        .cloned()
-        .unwrap_or_else(|| string_key.clone());
-    let index_key = ordered_carriers.get(0).cloned()?;
-
-    let s_loop = *name_to_loop_id.get(&string_key)?;
-    let i_loop = *name_to_loop_id.get(&index_key)?;
-    let n_loop = *name_to_loop_id.get(&len_key)?;
+    let s_loop = ctx.get_loop_id(&string_key)?;
+    let i_loop = ctx.get_loop_id(&index_key)?;
+    let n_loop = ctx.get_loop_id(&len_key)?;
 
     let mut join_module = JoinModule::new();
 
@@ -123,9 +89,10 @@ pub fn lower_case_a_loop_to_joinir_for_minimal_skip_ws(
     }));
 
     let loop_step_id = JoinFuncId::new(1);
-    let loop_call_args: Vec<ValueId> = ordered_pinned
+    let loop_call_args: Vec<ValueId> = ctx
+        .ordered_pinned
         .iter()
-        .chain(ordered_carriers.iter())
+        .chain(ctx.ordered_carriers.iter())
         .map(|name| entry_name_to_id.get(name).copied())
         .collect::<Option<_>>()?;
 
@@ -140,7 +107,7 @@ pub fn lower_case_a_loop_to_joinir_for_minimal_skip_ws(
     join_module.add_function(skip_func);
 
     // loop_step(s, i, n)
-    let header_shape = LoopHeaderShape::new_manual(pinned_ids.clone(), carrier_ids.clone());
+    let header_shape = LoopHeaderShape::new_manual(ctx.pinned_ids.clone(), ctx.carrier_ids.clone());
     let loop_params = header_shape.to_loop_step_params();
     let mut loop_step_func =
         JoinFunction::new(loop_step_id, "loop_step".to_string(), loop_params.clone());
@@ -164,10 +131,10 @@ pub fn lower_case_a_loop_to_joinir_for_minimal_skip_ws(
             rhs: n_loop,
         }));
 
-    let _exit_shape = if exit_args.is_empty() {
+    let _exit_shape = if ctx.exit_args.is_empty() {
         LoopExitShape::new_manual(vec![i_loop])
     } else {
-        LoopExitShape::new_manual(exit_args.clone())
+        LoopExitShape::new_manual(ctx.exit_args.clone())
     }; // exit_args = [i] が期待値
 
     // if i >= n { return i }
@@ -279,60 +246,24 @@ pub fn lower_case_a_loop_to_joinir_for_trim_minimal(
     query: &impl MirQuery,
     mir_func: &MirFunction,
 ) -> Option<JoinModule> {
-    if loop_form.header == loop_form.exit {
-        eprintln!("[joinir/generic_case_a/trim] loop_form malformed (header == exit), fallback");
-        return None;
-    }
+    // CaseAContext で共通ロジックを実行
+    let ctx = CaseAContext::new(
+        loop_form,
+        var_classes,
+        exit_live,
+        query,
+        mir_func,
+        "trim",
+        |offset| value_id_ranges::funcscanner_trim::loop_step(offset),
+    )?;
 
-    let LoopFormIntake {
-        pinned_ordered: ordered_pinned,
-        carrier_ordered: ordered_carriers,
-        name_to_header_id: _name_to_id,
-        header_snapshot,
-        exit_snapshots,
-        exit_preds: _exit_preds,
-    } = intake_loop_form(loop_form, var_classes, query, mir_func)?;
+    let string_key = ctx.pinned_name_or_first(0)?;
+    let base_key = ctx.pinned_name_or_first(1).unwrap_or_else(|| string_key.clone());
+    let carrier_key = ctx.carrier_name_or_first(0)?;
 
-    let mut name_to_loop_id: BTreeMap<String, ValueId> = BTreeMap::new();
-    let mut offset = 0;
-    for name in &ordered_pinned {
-        name_to_loop_id.insert(
-            name.clone(),
-            value_id_ranges::funcscanner_trim::loop_step(offset),
-        );
-        offset += 1;
-    }
-    for name in &ordered_carriers {
-        name_to_loop_id.insert(
-            name.clone(),
-            value_id_ranges::funcscanner_trim::loop_step(offset),
-        );
-        offset += 1;
-    }
-
-    let pinned_ids: Vec<ValueId> = ordered_pinned
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-    let carrier_ids: Vec<ValueId> = ordered_carriers
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-
-    let exit_live_set: BTreeSet<String> =
-        exit_live.compute_live_at_exit(query, loop_form.exit, &header_snapshot, &exit_snapshots);
-    let exit_args = resolve_exit_args(&exit_live_set, &name_to_loop_id, &ordered_carriers)?;
-
-    let string_key = ordered_pinned.get(0).cloned()?;
-    let base_key = ordered_pinned
-        .get(1)
-        .cloned()
-        .unwrap_or_else(|| string_key.clone());
-    let carrier_key = ordered_carriers.get(0).cloned()?;
-
-    let s_loop = *name_to_loop_id.get(&string_key)?;
-    let b_loop = *name_to_loop_id.get(&base_key)?;
-    let e_loop = *name_to_loop_id.get(&carrier_key)?;
+    let s_loop = ctx.get_loop_id(&string_key)?;
+    let b_loop = ctx.get_loop_id(&base_key)?;
+    let e_loop = ctx.get_loop_id(&carrier_key)?;
 
     let mut join_module = JoinModule::new();
 
@@ -400,9 +331,10 @@ pub fn lower_case_a_loop_to_joinir_for_trim_minimal(
     entry_name_to_id.insert(base_key.clone(), b_val);
     entry_name_to_id.insert(carrier_key.clone(), e_init);
 
-    let loop_call_args: Vec<ValueId> = ordered_pinned
+    let loop_call_args: Vec<ValueId> = ctx
+        .ordered_pinned
         .iter()
-        .chain(ordered_carriers.iter())
+        .chain(ctx.ordered_carriers.iter())
         .map(|name| entry_name_to_id.get(name).copied())
         .collect::<Option<_>>()?;
 
@@ -418,7 +350,7 @@ pub fn lower_case_a_loop_to_joinir_for_trim_minimal(
     join_module.add_function(trim_main_func);
 
     // loop_step(str, b, e)
-    let header_shape = LoopHeaderShape::new_manual(pinned_ids.clone(), carrier_ids.clone());
+    let header_shape = LoopHeaderShape::new_manual(ctx.pinned_ids.clone(), ctx.carrier_ids.clone());
     let loop_params = header_shape.to_loop_step_params();
     let mut loop_step_func =
         JoinFunction::new(loop_step_id, "loop_step".to_string(), loop_params.clone());
@@ -461,10 +393,10 @@ pub fn lower_case_a_loop_to_joinir_for_trim_minimal(
             op: CompareOp::Eq,
         }));
 
-    let _exit_shape_trim = if exit_args.is_empty() {
+    let _exit_shape_trim = if ctx.exit_args.is_empty() {
         LoopExitShape::new_manual(vec![e_loop])
     } else {
-        LoopExitShape::new_manual(exit_args.clone())
+        LoopExitShape::new_manual(ctx.exit_args.clone())
     };
 
     loop_step_func.body.push(JoinInst::Jump {
@@ -794,67 +726,26 @@ pub fn lower_case_a_loop_to_joinir_for_append_defs_minimal(
     query: &impl MirQuery,
     mir_func: &MirFunction,
 ) -> Option<JoinModule> {
-    if loop_form.header == loop_form.exit {
-        eprintln!(
-            "[joinir/generic_case_a/append_defs] loop_form malformed (header == exit), fallback"
-        );
-        return None;
-    }
+    // CaseAContext で共通ロジックを実行
+    let ctx = CaseAContext::new(
+        loop_form,
+        var_classes,
+        exit_live,
+        query,
+        mir_func,
+        "append_defs",
+        |offset| value_id_ranges::funcscanner_append_defs::loop_step(offset),
+    )?;
 
-    let LoopFormIntake {
-        pinned_ordered: ordered_pinned,
-        carrier_ordered: ordered_carriers,
-        name_to_header_id: _name_to_id,
-        header_snapshot,
-        exit_snapshots,
-        exit_preds: _exit_preds,
-    } = intake_loop_form(loop_form, var_classes, query, mir_func)?;
+    let dst_key = ctx.pinned_name_or_first(0)?;
+    let defs_key = ctx.pinned_name_or_first(1).unwrap_or_else(|| dst_key.clone());
+    let n_key = ctx.pinned_name_or_first(2).unwrap_or_else(|| defs_key.clone());
+    let i_key = ctx.carrier_name_or_first(0)?;
 
-    let mut name_to_loop_id: BTreeMap<String, ValueId> = BTreeMap::new();
-    let mut offset = 0;
-    for name in &ordered_pinned {
-        name_to_loop_id.insert(
-            name.clone(),
-            value_id_ranges::funcscanner_append_defs::loop_step(offset),
-        );
-        offset += 1;
-    }
-    for name in &ordered_carriers {
-        name_to_loop_id.insert(
-            name.clone(),
-            value_id_ranges::funcscanner_append_defs::loop_step(offset),
-        );
-        offset += 1;
-    }
-
-    let pinned_ids: Vec<ValueId> = ordered_pinned
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-    let carrier_ids: Vec<ValueId> = ordered_carriers
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-
-    let exit_live_set: BTreeSet<String> =
-        exit_live.compute_live_at_exit(query, loop_form.exit, &header_snapshot, &exit_snapshots);
-    let exit_args = resolve_exit_args(&exit_live_set, &name_to_loop_id, &ordered_carriers)?;
-
-    let dst_key = ordered_pinned.get(0).cloned()?;
-    let defs_key = ordered_pinned
-        .get(1)
-        .cloned()
-        .unwrap_or_else(|| dst_key.clone());
-    let n_key = ordered_pinned
-        .get(2)
-        .cloned()
-        .unwrap_or_else(|| defs_key.clone());
-    let i_key = ordered_carriers.get(0).cloned()?;
-
-    let dst_loop = *name_to_loop_id.get(&dst_key)?;
-    let defs_loop = *name_to_loop_id.get(&defs_key)?;
-    let n_loop = *name_to_loop_id.get(&n_key)?;
-    let i_loop = *name_to_loop_id.get(&i_key)?;
+    let dst_loop = ctx.get_loop_id(&dst_key)?;
+    let defs_loop = ctx.get_loop_id(&defs_key)?;
+    let n_loop = ctx.get_loop_id(&n_key)?;
+    let i_loop = ctx.get_loop_id(&i_key)?;
 
     let mut join_module = JoinModule::new();
 
@@ -882,9 +773,10 @@ pub fn lower_case_a_loop_to_joinir_for_append_defs_minimal(
     entry_name_to_id.insert("n".to_string(), n_param);
     entry_name_to_id.insert("i".to_string(), i_init);
 
-    let loop_call_args: Vec<ValueId> = ordered_pinned
+    let loop_call_args: Vec<ValueId> = ctx
+        .ordered_pinned
         .iter()
-        .chain(ordered_carriers.iter())
+        .chain(ctx.ordered_carriers.iter())
         .map(|name| entry_name_to_id.get(name).copied())
         .collect::<Option<_>>()?;
 
@@ -900,7 +792,7 @@ pub fn lower_case_a_loop_to_joinir_for_append_defs_minimal(
     join_module.add_function(entry_func);
 
     // loop_step(dst, defs_box, n, i)
-    let header_shape = LoopHeaderShape::new_manual(pinned_ids.clone(), carrier_ids.clone());
+    let header_shape = LoopHeaderShape::new_manual(ctx.pinned_ids.clone(), ctx.carrier_ids.clone());
     let loop_params = header_shape.to_loop_step_params();
     let mut loop_step_func =
         JoinFunction::new(loop_step_id, "loop_step".to_string(), loop_params.clone());
@@ -915,11 +807,11 @@ pub fn lower_case_a_loop_to_joinir_for_append_defs_minimal(
             rhs: n_loop,
         }));
 
-    let _exit_shape = LoopExitShape::new_manual(exit_args.clone());
+    let _exit_shape = LoopExitShape::new_manual(ctx.exit_args.clone());
 
     loop_step_func.body.push(JoinInst::Jump {
         cont: JoinContId::new(0),
-        args: exit_args.clone(),
+        args: ctx.exit_args.clone(),
         cond: Some(cmp_result),
     });
 
@@ -988,69 +880,30 @@ pub fn lower_case_a_loop_to_joinir_for_stage1_usingresolver_minimal(
     query: &impl MirQuery,
     mir_func: &MirFunction,
 ) -> Option<JoinModule> {
-    if loop_form.header == loop_form.exit {
-        eprintln!("[joinir/generic_case_a/stage1] loop_form malformed (header == exit), fallback");
-        return None;
-    }
+    // CaseAContext で共通ロジックを実行
+    let ctx = CaseAContext::new(
+        loop_form,
+        var_classes,
+        exit_live,
+        query,
+        mir_func,
+        "stage1",
+        |offset| stage1_vid::loop_step(offset),
+    )?;
 
-    let LoopFormIntake {
-        pinned_ordered: ordered_pinned,
-        carrier_ordered: ordered_carriers,
-        name_to_header_id: _name_to_id,
-        header_snapshot,
-        exit_snapshots,
-        exit_preds: _exit_preds,
-    } = intake_loop_form(loop_form, var_classes, query, mir_func)?;
+    let entries_key = ctx.pinned_name_or_first(0)?;
+    let n_key = ctx.pinned_name_or_first(1).unwrap_or_else(|| entries_key.clone());
+    let modules_key = ctx.pinned_name_or_first(2).unwrap_or_else(|| entries_key.clone());
+    let seen_key = ctx.pinned_name_or_first(3).unwrap_or_else(|| entries_key.clone());
+    let prefix_key = ctx.carrier_name_or_first(0)?;
+    let i_key = ctx.carrier_name_or_first(1).unwrap_or_else(|| prefix_key.clone());
 
-    let mut name_to_loop_id: BTreeMap<String, ValueId> = BTreeMap::new();
-    let mut offset = 0;
-    for name in &ordered_pinned {
-        name_to_loop_id.insert(name.clone(), stage1_vid::loop_step(offset));
-        offset += 1;
-    }
-    for name in &ordered_carriers {
-        name_to_loop_id.insert(name.clone(), stage1_vid::loop_step(offset));
-        offset += 1;
-    }
-
-    let pinned_ids: Vec<ValueId> = ordered_pinned
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-    let carrier_ids: Vec<ValueId> = ordered_carriers
-        .iter()
-        .filter_map(|k| name_to_loop_id.get(k).copied())
-        .collect();
-
-    let exit_live_set: BTreeSet<String> =
-        exit_live.compute_live_at_exit(query, loop_form.exit, &header_snapshot, &exit_snapshots);
-    let exit_args = resolve_exit_args(&exit_live_set, &name_to_loop_id, &ordered_carriers)?;
-
-    let entries_key = ordered_pinned.get(0).cloned()?;
-    let n_key = ordered_pinned
-        .get(1)
-        .cloned()
-        .unwrap_or_else(|| entries_key.clone());
-    let modules_key = ordered_pinned
-        .get(2)
-        .cloned()
-        .unwrap_or_else(|| entries_key.clone());
-    let seen_key = ordered_pinned
-        .get(3)
-        .cloned()
-        .unwrap_or_else(|| entries_key.clone());
-    let prefix_key = ordered_carriers.get(0).cloned()?;
-    let i_key = ordered_carriers
-        .get(1)
-        .cloned()
-        .unwrap_or_else(|| prefix_key.clone());
-
-    let entries_loop = *name_to_loop_id.get(&entries_key)?;
-    let n_loop = *name_to_loop_id.get(&n_key)?;
-    let modules_loop = *name_to_loop_id.get(&modules_key)?;
-    let seen_loop = *name_to_loop_id.get(&seen_key)?;
-    let prefix_loop = *name_to_loop_id.get(&prefix_key)?;
-    let i_loop = *name_to_loop_id.get(&i_key)?;
+    let entries_loop = ctx.get_loop_id(&entries_key)?;
+    let n_loop = ctx.get_loop_id(&n_key)?;
+    let modules_loop = ctx.get_loop_id(&modules_key)?;
+    let seen_loop = ctx.get_loop_id(&seen_key)?;
+    let prefix_loop = ctx.get_loop_id(&prefix_key)?;
+    let i_loop = ctx.get_loop_id(&i_key)?;
 
     let mut join_module = JoinModule::new();
 
@@ -1089,9 +942,10 @@ pub fn lower_case_a_loop_to_joinir_for_stage1_usingresolver_minimal(
     entry_name_to_id.insert(prefix_key.clone(), prefix_param);
     entry_name_to_id.insert(i_key.clone(), i_init);
 
-    let loop_call_args: Vec<ValueId> = ordered_pinned
+    let loop_call_args: Vec<ValueId> = ctx
+        .ordered_pinned
         .iter()
-        .chain(ordered_carriers.iter())
+        .chain(ctx.ordered_carriers.iter())
         .map(|name| entry_name_to_id.get(name).copied())
         .collect::<Option<_>>()?;
 
@@ -1107,7 +961,7 @@ pub fn lower_case_a_loop_to_joinir_for_stage1_usingresolver_minimal(
     join_module.add_function(resolve_func);
 
     // loop_step(entries, n, modules, seen, prefix, i)
-    let header_shape = LoopHeaderShape::new_manual(pinned_ids.clone(), carrier_ids.clone());
+    let header_shape = LoopHeaderShape::new_manual(ctx.pinned_ids.clone(), ctx.carrier_ids.clone());
     let loop_params = header_shape.to_loop_step_params();
     let mut loop_step_func =
         JoinFunction::new(loop_step_id, "loop_step".to_string(), loop_params.clone());
@@ -1122,10 +976,10 @@ pub fn lower_case_a_loop_to_joinir_for_stage1_usingresolver_minimal(
             rhs: n_loop,
         }));
 
-    let exit_shape = if exit_args.is_empty() {
+    let exit_shape = if ctx.exit_args.is_empty() {
         LoopExitShape::new_manual(vec![prefix_loop])
     } else {
-        LoopExitShape::new_manual(exit_args.clone())
+        LoopExitShape::new_manual(ctx.exit_args.clone())
     };
 
     loop_step_func.body.push(JoinInst::Jump {
diff --git a/src/mir/join_ir/lowering/loop_form_intake.rs b/src/mir/join_ir/lowering/loop_form_intake.rs
index b49a37e2..d0cefc77 100644
--- a/src/mir/join_ir/lowering/loop_form_intake.rs
+++ b/src/mir/join_ir/lowering/loop_form_intake.rs
@@ -14,7 +14,6 @@ use std::collections::{BTreeMap, BTreeSet};
 pub(crate) struct LoopFormIntake {
     pub pinned_ordered: Vec<String>,
     pub carrier_ordered: Vec<String>,
-    pub name_to_header_id: BTreeMap<String, ValueId>,
     pub header_snapshot: BTreeMap<String, ValueId>,
     pub exit_snapshots: Vec<(BasicBlockId, BTreeMap<String, ValueId>)>,
     pub exit_preds: Vec<BasicBlockId>,
@@ -204,7 +203,6 @@ pub(crate) fn intake_loop_form(
     Some(LoopFormIntake {
         pinned_ordered: ordered_pinned,
         carrier_ordered: ordered_carriers,
-        name_to_header_id: header_vals_mir.clone(),
         header_snapshot: header_vals_mir,
         exit_snapshots,
         exit_preds,
diff --git a/src/mir/join_ir/lowering/loop_scope_shape.rs b/src/mir/join_ir/lowering/loop_scope_shape.rs
new file mode 100644
index 00000000..bcb512c5
--- /dev/null
+++ b/src/mir/join_ir/lowering/loop_scope_shape.rs
@@ -0,0 +1,499 @@
+//! LoopScopeShape - ループ変数スコープの統合ビュー
+//!
+//! # Purpose
+//!
+//! 既存の3箱（LoopVarClassBox, LoopExitLivenessBox, LocalScopeInspectorBox）の
+//! 情報を1つの構造体に統合し、JoinIR lowering が参照する唯一のソースにする。
+//!
+//! # Design Philosophy (Box-First)
+//!
+//! Phase 29/30 で以下の責務分離を実現:
+//! - LoopForm: ループの「形」（preheader/header/body/latch/exit）
+//! - LoopScopeShape: 変数の「役割」（pinned/carrier/body_local/exit_live）
+//! - JoinIR: 関数と継続で表現された制御構造
+//!
+//! # Phase 29 Strategy
+//!
+//! 現在は「既存箱を呼ぶだけの薄いラッパー」として実装。
+//! 将来は既存箱を吸収して LoopScopeShape を唯一のソースにする（Phase 30）。
+//!
+//! # Usage
+//!
+//! ```ignore
+//! let scope = LoopScopeShape::from_existing_boxes(
+//!     &loop_form_intake,
+//!     &var_classes,
+//!     &exit_live,
+//!     query,
+//! )?;
+//!
+//! // JoinIR lowering では scope のフィールドを参照
+//! for name in &scope.pinned {
+//!     // ...
+//! }
+//! ```
+
+use std::collections::{BTreeMap, BTreeSet};
+
+use crate::mir::join_ir::lowering::exit_args_resolver::resolve_exit_args;
+use crate::mir::join_ir::lowering::loop_form_intake::{intake_loop_form, LoopFormIntake};
+use crate::mir::loop_form::LoopForm;
+use crate::mir::phi_core::loop_exit_liveness::LoopExitLivenessBox;
+use crate::mir::phi_core::loop_var_classifier::{LoopVarClass, LoopVarClassBox};
+use crate::mir::{BasicBlockId, MirFunction, MirQuery, ValueId};
+
+/// ループ変数スコープの統合ビュー
+///
+/// # Fields
+///
+/// - `pinned`: ループ外から来て変わらない変数（header/exit PHI 両方必要）
+/// - `carriers`: 各イテレーションで更新される変数（header/exit PHI 両方必要）
+/// - `body_locals`: ループ内だけで完結する変数（JoinIR では参照しない）
+/// - `exit_live`: ループ後に使われる変数（needs_exit_phi() == true）
+/// - `progress_carrier`: ループを前に進める変数（将来の Verifier 用）
+#[derive(Debug, Clone)]
+pub(crate) struct LoopScopeShape {
+    /// Loop-crossing parameters (always need header/exit PHI)
+    pub pinned: BTreeSet<String>,
+
+    /// Loop-modified variables (always need header/exit PHI)
+    pub carriers: BTreeSet<String>,
+
+    /// Body-local variables (JoinIR doesn't need these)
+    /// Includes both BodyLocalExit and BodyLocalInternal
+    pub body_locals: BTreeSet<String>,
+
+    /// Variables live at exit (needs_exit_phi() == true)
+    /// = pinned ∪ carriers ∪ BodyLocalExit
+    pub exit_live: BTreeSet<String>,
+
+    /// Progress carrier for loop termination check (future Verifier use)
+    /// Typically the loop index variable (i, pos, etc.)
+    pub progress_carrier: Option<String>,
+}
+
+impl LoopScopeShape {
+    /// Create LoopScopeShape from existing boxes (Phase 29: thin wrapper)
+    ///
+    /// # Arguments
+    ///
+    /// - `intake`: LoopFormIntake containing classified variable info
+    /// - `var_classes`: LoopVarClassBox for classification
+    /// - `exit_live_box`: LoopExitLivenessBox for exit liveness
+    /// - `query`: MirQuery for liveness computation
+    /// - `exit_block`: Exit block ID
+    ///
+    /// # Returns
+    ///
+    /// Some(LoopScopeShape) if successful, None if critical data is missing.
+    ///
+    /// # Phase 29 Behavior
+    ///
+    /// Currently just reads from existing boxes without modifying behavior.
+    /// Future Phase 30 will absorb the boxes entirely.
+    pub(crate) fn from_existing_boxes(
+        intake: &LoopFormIntake,
+        var_classes: &LoopVarClassBox,
+        exit_live_box: &LoopExitLivenessBox,
+        query: &impl MirQuery,
+        exit_block: BasicBlockId,
+    ) -> Option<Self> {
+        // Extract pinned and carriers from intake (already classified)
+        let pinned: BTreeSet<String> = intake.pinned_ordered.iter().cloned().collect();
+        let carriers: BTreeSet<String> = intake.carrier_ordered.iter().cloned().collect();
+
+        // Build LocalScopeInspectorBox for body_local classification
+        let mut inspector =
+            crate::mir::phi_core::local_scope_inspector::LocalScopeInspectorBox::new();
+        inspector.record_snapshot(exit_block, &intake.header_snapshot);
+        for (bb, snap) in &intake.exit_snapshots {
+            inspector.record_snapshot(*bb, snap);
+        }
+
+        // Classify all variables to find body_locals
+        let all_names: Vec<String> = intake.header_snapshot.keys().cloned().collect();
+        let classified = var_classes.classify_all(
+            &all_names,
+            &intake.pinned_ordered,
+            &intake.carrier_ordered,
+            &inspector,
+            &intake.exit_preds,
+        );
+
+        let mut body_locals: BTreeSet<String> = BTreeSet::new();
+        let mut exit_live: BTreeSet<String> = BTreeSet::new();
+
+        for (name, class) in &classified {
+            match class {
+                LoopVarClass::Pinned => {
+                    exit_live.insert(name.clone());
+                }
+                LoopVarClass::Carrier => {
+                    exit_live.insert(name.clone());
+                }
+                LoopVarClass::BodyLocalExit => {
+                    body_locals.insert(name.clone());
+                    exit_live.insert(name.clone());
+                }
+                LoopVarClass::BodyLocalInternal => {
+                    body_locals.insert(name.clone());
+                    // NOT in exit_live (Option C: skip exit PHI)
+                }
+            }
+        }
+
+        // Compute exit_live from LoopExitLivenessBox (Phase 1: usually empty)
+        let exit_live_from_box = exit_live_box.compute_live_at_exit(
+            query,
+            exit_block,
+            &intake.header_snapshot,
+            &intake.exit_snapshots,
+        );
+
+        // Merge: exit_live = (classification-based) ∪ (liveness-box-based)
+        for name in exit_live_from_box {
+            exit_live.insert(name);
+        }
+
+        // Determine progress_carrier (heuristic: first carrier, typically 'i')
+        let progress_carrier = carriers.iter().next().cloned();
+
+        Some(Self {
+            pinned,
+            carriers,
+            body_locals,
+            exit_live,
+            progress_carrier,
+        })
+    }
+
+    /// Check if a variable needs header PHI
+    pub fn needs_header_phi(&self, var_name: &str) -> bool {
+        self.pinned.contains(var_name) || self.carriers.contains(var_name)
+    }
+
+    /// Check if a variable needs exit PHI
+    pub fn needs_exit_phi(&self, var_name: &str) -> bool {
+        self.exit_live.contains(var_name)
+    }
+
+    /// Get ordered pinned variables (for JoinIR parameter generation)
+    pub fn pinned_ordered(&self) -> Vec<String> {
+        self.pinned.iter().cloned().collect()
+    }
+
+    /// Get ordered carrier variables (for JoinIR parameter generation)
+    pub fn carriers_ordered(&self) -> Vec<String> {
+        self.carriers.iter().cloned().collect()
+    }
+
+    /// Get all variables that need header PHI (pinned + carriers)
+    pub fn header_phi_vars(&self) -> Vec<String> {
+        let mut result: Vec<String> = self.pinned.iter().cloned().collect();
+        result.extend(self.carriers.iter().cloned());
+        result
+    }
+
+    /// Get all variables that need exit PHI
+    pub fn exit_phi_vars(&self) -> Vec<String> {
+        self.exit_live.iter().cloned().collect()
+    }
+}
+
+// ============================================================================
+// CaseAContext - generic_case_a 共通ロジックの集約
+// ============================================================================
+
+/// Case A lowering の共通コンテキスト
+///
+/// generic_case_a.rs の4関数に共通するロジックを集約し、
+/// 約200行の重複コードを削減する。
+///
+/// # Usage
+///
+/// ```ignore
+/// let ctx = CaseAContext::new(
+///     loop_form, var_classes, exit_live, query, mir_func,
+///     "skip_ws",
+///     |offset| vid::loop_step(offset),
+/// )?;
+///
+/// // ctx から必要な情報を取り出して JoinModule を構築
+/// let header_shape = LoopHeaderShape::new_manual(ctx.pinned_ids.clone(), ctx.carrier_ids.clone());
+/// ```
+#[derive(Debug, Clone)]
+pub(crate) struct CaseAContext {
+    /// LoopScopeShape（変数スコープ情報）
+    pub scope: LoopScopeShape,
+
+    /// 順序付き pinned 変数名
+    pub ordered_pinned: Vec<String>,
+
+    /// 順序付き carrier 変数名
+    pub ordered_carriers: Vec<String>,
+
+    /// 変数名 → ループ関数内 ValueId のマッピング
+    pub name_to_loop_id: BTreeMap<String, ValueId>,
+
+    /// pinned 変数の ValueId 列
+    pub pinned_ids: Vec<ValueId>,
+
+    /// carrier 変数の ValueId 列
+    pub carrier_ids: Vec<ValueId>,
+
+    /// exit 時に渡す引数の ValueId 列
+    pub exit_args: Vec<ValueId>,
+}
+
+impl CaseAContext {
+    /// CaseAContext を構築する
+    ///
+    /// # Arguments
+    ///
+    /// - `loop_form`: ループ構造情報
+    /// - `var_classes`: 変数分類器
+    /// - `exit_live`: exit liveness 情報
+    /// - `query`: MIR クエリ
+    /// - `mir_func`: MIR 関数
+    /// - `log_tag`: ログ出力用タグ（例: "skip_ws", "trim"）
+    /// - `loop_step_id_fn`: offset から ValueId を生成する関数
+    ///
+    /// # Returns
+    ///
+    /// Some(CaseAContext) if successful, None if validation fails or data is missing.
+    pub(crate) fn new<F>(
+        loop_form: &LoopForm,
+        var_classes: &LoopVarClassBox,
+        exit_live: &LoopExitLivenessBox,
+        query: &impl MirQuery,
+        mir_func: &MirFunction,
+        log_tag: &str,
+        loop_step_id_fn: F,
+    ) -> Option<Self>
+    where
+        F: Fn(u32) -> ValueId,
+    {
+        // 1) LoopForm validation
+        if loop_form.header == loop_form.exit {
+            eprintln!(
+                "[joinir/generic_case_a/{}] loop_form malformed (header == exit), fallback",
+                log_tag
+            );
+            return None;
+        }
+
+        // 2) MIR から pinned/carrier/exit 情報を抽出
+        let intake = intake_loop_form(loop_form, var_classes, query, mir_func)?;
+
+        // 3) LoopScopeShape を構築
+        let scope = LoopScopeShape::from_existing_boxes(
+            &intake,
+            var_classes,
+            exit_live,
+            query,
+            loop_form.exit,
+        )?;
+
+        let ordered_pinned = scope.pinned_ordered();
+        let ordered_carriers = scope.carriers_ordered();
+
+        // 4) 変数名 → ValueId マッピングを構築
+        let mut name_to_loop_id: BTreeMap<String, ValueId> = BTreeMap::new();
+        let mut offset: u32 = 0;
+        for name in &ordered_pinned {
+            name_to_loop_id.insert(name.clone(), loop_step_id_fn(offset));
+            offset += 1;
+        }
+        for name in &ordered_carriers {
+            name_to_loop_id.insert(name.clone(), loop_step_id_fn(offset));
+            offset += 1;
+        }
+
+        // 5) pinned_ids / carrier_ids を構築
+        let pinned_ids: Vec<ValueId> = ordered_pinned
+            .iter()
+            .filter_map(|k| name_to_loop_id.get(k).copied())
+            .collect();
+        let carrier_ids: Vec<ValueId> = ordered_carriers
+            .iter()
+            .filter_map(|k| name_to_loop_id.get(k).copied())
+            .collect();
+
+        // 6) exit_args を解決
+        let exit_args = resolve_exit_args(&scope.exit_live, &name_to_loop_id, &ordered_carriers)?;
+
+        Some(Self {
+            scope,
+            ordered_pinned,
+            ordered_carriers,
+            name_to_loop_id,
+            pinned_ids,
+            carrier_ids,
+            exit_args,
+        })
+    }
+
+    /// 変数名から loop 関数内の ValueId を取得
+    pub fn get_loop_id(&self, name: &str) -> Option<ValueId> {
+        self.name_to_loop_id.get(name).copied()
+    }
+
+    /// pinned 変数の n 番目の名前を取得（なければ 0 番目を使う）
+    pub fn pinned_name_or_first(&self, index: usize) -> Option<String> {
+        self.ordered_pinned
+            .get(index)
+            .cloned()
+            .or_else(|| self.ordered_pinned.first().cloned())
+    }
+
+    /// carrier 変数の n 番目の名前を取得（なければ 0 番目を使う）
+    pub fn carrier_name_or_first(&self, index: usize) -> Option<String> {
+        self.ordered_carriers
+            .get(index)
+            .cloned()
+            .or_else(|| self.ordered_carriers.first().cloned())
+    }
+}
+
+// ============================================================================
+// Unit Tests
+// ============================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::mir::ValueId;
+    use std::collections::BTreeMap;
+
+    fn make_dummy_intake() -> LoopFormIntake {
+        let mut header_snapshot = BTreeMap::new();
+        header_snapshot.insert("s".to_string(), ValueId(10));
+        header_snapshot.insert("n".to_string(), ValueId(20));
+        header_snapshot.insert("i".to_string(), ValueId(30));
+
+        LoopFormIntake {
+            pinned_ordered: vec!["s".to_string(), "n".to_string()],
+            carrier_ordered: vec!["i".to_string()],
+            header_snapshot,
+            exit_snapshots: vec![],
+            exit_preds: vec![],
+        }
+    }
+
+    struct EmptyQuery;
+    impl MirQuery for EmptyQuery {
+        fn insts_in_block(&self, _bb: BasicBlockId) -> &[crate::mir::MirInstruction] {
+            &[]
+        }
+        fn succs(&self, _bb: BasicBlockId) -> Vec<BasicBlockId> {
+            Vec::new()
+        }
+        fn reads_of(&self, _inst: &crate::mir::MirInstruction) -> Vec<ValueId> {
+            Vec::new()
+        }
+        fn writes_of(&self, _inst: &crate::mir::MirInstruction) -> Vec<ValueId> {
+            Vec::new()
+        }
+    }
+
+    #[test]
+    fn test_from_existing_boxes_basic() {
+        let intake = make_dummy_intake();
+        let var_classes = LoopVarClassBox::new();
+        let exit_live_box = LoopExitLivenessBox::new();
+        let query = EmptyQuery;
+
+        let scope = LoopScopeShape::from_existing_boxes(
+            &intake,
+            &var_classes,
+            &exit_live_box,
+            &query,
+            BasicBlockId::new(100),
+        );
+
+        assert!(scope.is_some());
+        let scope = scope.unwrap();
+
+        // pinned should be {s, n}
+        assert!(scope.pinned.contains("s"));
+        assert!(scope.pinned.contains("n"));
+        assert_eq!(scope.pinned.len(), 2);
+
+        // carriers should be {i}
+        assert!(scope.carriers.contains("i"));
+        assert_eq!(scope.carriers.len(), 1);
+
+        // progress_carrier should be "i"
+        assert_eq!(scope.progress_carrier, Some("i".to_string()));
+    }
+
+    #[test]
+    fn test_needs_header_phi() {
+        let intake = make_dummy_intake();
+        let var_classes = LoopVarClassBox::new();
+        let exit_live_box = LoopExitLivenessBox::new();
+        let query = EmptyQuery;
+
+        let scope = LoopScopeShape::from_existing_boxes(
+            &intake,
+            &var_classes,
+            &exit_live_box,
+            &query,
+            BasicBlockId::new(100),
+        )
+        .unwrap();
+
+        assert!(scope.needs_header_phi("s"));
+        assert!(scope.needs_header_phi("n"));
+        assert!(scope.needs_header_phi("i"));
+        assert!(!scope.needs_header_phi("unknown"));
+    }
+
+    #[test]
+    fn test_needs_exit_phi() {
+        let intake = make_dummy_intake();
+        let var_classes = LoopVarClassBox::new();
+        let exit_live_box = LoopExitLivenessBox::new();
+        let query = EmptyQuery;
+
+        let scope = LoopScopeShape::from_existing_boxes(
+            &intake,
+            &var_classes,
+            &exit_live_box,
+            &query,
+            BasicBlockId::new(100),
+        )
+        .unwrap();
+
+        // Pinned and Carrier should need exit PHI
+        assert!(scope.needs_exit_phi("s"));
+        assert!(scope.needs_exit_phi("n"));
+        assert!(scope.needs_exit_phi("i"));
+    }
+
+    #[test]
+    fn test_ordered_accessors() {
+        let intake = make_dummy_intake();
+        let var_classes = LoopVarClassBox::new();
+        let exit_live_box = LoopExitLivenessBox::new();
+        let query = EmptyQuery;
+
+        let scope = LoopScopeShape::from_existing_boxes(
+            &intake,
+            &var_classes,
+            &exit_live_box,
+            &query,
+            BasicBlockId::new(100),
+        )
+        .unwrap();
+
+        let pinned = scope.pinned_ordered();
+        assert_eq!(pinned.len(), 2);
+        assert!(pinned.contains(&"s".to_string()));
+        assert!(pinned.contains(&"n".to_string()));
+
+        let carriers = scope.carriers_ordered();
+        assert_eq!(carriers.len(), 1);
+        assert!(carriers.contains(&"i".to_string()));
+    }
+}
diff --git a/src/mir/join_ir/lowering/mod.rs b/src/mir/join_ir/lowering/mod.rs
index 5d24d16d..97e5753a 100644
--- a/src/mir/join_ir/lowering/mod.rs
+++ b/src/mir/join_ir/lowering/mod.rs
@@ -19,6 +19,7 @@ pub mod funcscanner_append_defs;
 pub mod funcscanner_trim;
 pub mod generic_case_a;
 pub mod loop_form_intake;
+pub mod loop_scope_shape;
 pub mod min_loop;
 pub mod skip_ws;
 pub mod stage1_using_resolver;