diff --git a/src/mir/builder/control_flow/joinir/patterns/loop_scope_shape_builder.rs b/src/mir/builder/control_flow/joinir/patterns/loop_scope_shape_builder.rs
index fad37b2c..feb18602 100644
--- a/src/mir/builder/control_flow/joinir/patterns/loop_scope_shape_builder.rs
+++ b/src/mir/builder/control_flow/joinir/patterns/loop_scope_shape_builder.rs
@@ -1,4 +1,4 @@
-//! LoopScopeShapeBuilder - Unified LoopScopeShape initialization
+//! LoopScopeShapeBuilder - AST-based LoopScopeShape initialization
 //!
 //! Phase 171-172: Issue 4
 //!
@@ -11,6 +11,14 @@
 //! - Extract body_locals from loop body AST when needed
 //! - Maintain consistent initialization defaults across patterns
 //!
+//! # Phase 183-3: AST-Based Construction Context
+//!
+//! This builder constructs LoopScopeShape from **AST nodes** during MIR building.
+//! For LoopForm-based construction (JoinIR lowering), see:
+//! - `src/mir/join_ir/lowering/loop_scope_shape/builder.rs`
+//!
+//! Both builders maintain consistent field initialization for LoopScopeShape.
+//!
 //! # Usage
 //!
 //! ```rust
diff --git a/src/mir/join_ir/lowering/loop_scope_shape/builder.rs b/src/mir/join_ir/lowering/loop_scope_shape/builder.rs
index 51b3dbc5..eb9767ad 100644
--- a/src/mir/join_ir/lowering/loop_scope_shape/builder.rs
+++ b/src/mir/join_ir/lowering/loop_scope_shape/builder.rs
@@ -6,6 +6,14 @@
 //! Trio legacy boxes は完全に除去済み。
 //! LoopForm / LoopFormIntake から LoopScopeShape を構築し、変数分類と定義位置を
 //! LoopScopeShape の内部に閉じ込める。
+//!
+//! # Phase 183-3: LoopForm-Based Construction Context
+//!
+//! This builder constructs LoopScopeShape from **LoopForm** during JoinIR lowering.
+//! For AST-based construction (MIR building), see:
+//! - `src/mir/builder/control_flow/joinir/patterns/loop_scope_shape_builder.rs`
+//!
+//! Both builders maintain consistent field initialization for LoopScopeShape.
 
 use std::collections::{BTreeMap, BTreeSet};
 
diff --git a/src/mir/join_ir/lowering/loop_scope_shape/shape.rs b/src/mir/join_ir/lowering/loop_scope_shape/shape.rs
index 91536bcf..83434b90 100644
--- a/src/mir/join_ir/lowering/loop_scope_shape/shape.rs
+++ b/src/mir/join_ir/lowering/loop_scope_shape/shape.rs
@@ -56,6 +56,20 @@ impl LoopVarClass {
 /// - Variable classification: `pinned`, `carriers`, `body_locals`, `exit_live`
 /// - `progress_carrier`: 進捗チェック用（将来の Verifier で使用予定）
 /// - `variable_definitions`: definition blocks collected from LoopFormIntake snapshots
+///
+/// # Phase 183-3: Construction Paths
+///
+/// LoopScopeShape has two construction paths depending on context:
+///
+/// 1. **AST-based** (MIR building): `patterns/loop_scope_shape_builder.rs`
+///    - Extracts body_locals from AST nodes
+///    - Used during initial MIR generation from source
+///
+/// 2. **LoopForm-based** (JoinIR lowering): `loop_scope_shape/builder.rs`
+///    - Analyzes LoopForm and LoopFormIntake
+///    - Used during JoinIR lowering from LoopForm
+///
+/// Both paths maintain consistent field initialization and variable classification.
 #[derive(Debug, Clone)]
 pub(crate) struct LoopScopeShape {
     pub header: BasicBlockId,