diff --git a/CURRENT_TASK.md b/CURRENT_TASK.md
index 104857fc..3581ba0a 100644
--- a/CURRENT_TASK.md
+++ b/CURRENT_TASK.md
@@ -216,10 +216,21 @@
    - Phase 53 で実戦ループ追加済みのため、追加投入より先に構造判定精度の測定に集中。
    - 構造シグネチャ軸を 5+ に拡張（Compare op 分布など）し、P2/P3 の偽陽性観測テストを追加。
    - 結果: selfhost 群の構造判定だけでは分離が不十分（偽陽性率 ~50%）。dev-only name ガードは当面必須と判断。
-12. **Phase 55-SELFHOST-SHAPE-AXIS-EXPAND（次のフォーカス候補・dev-only）**: 構造軸 8+ へ拡張し誤判定を下げる足場
-   - 条件複雑度（ネスト/論理結合の形）、算術更新パターン、分岐ファンアウトなどの新軸を追加。
-   - selfhost/canonical の feature ベクトル比較と観測テストを拡充し、name ガード縮小の根拠を作る（撤去は後続）。
-13. JoinIR Verify / 最適化まわり
+12. **Phase 55-SELFHOST-SHAPE-AXIS-EXPAND（dev-only / 保留）**: 構造軸を可変 feature として拡張し誤判定を下げる足場
+   - Phase 56–61 の Ownership-Relay ライン優先のため、selfhost shape 軸拡張は一旦保留。
+   - OwnershipAnalyzer 導入後に、scope 署名（owned/carriers/captures/relay）を新しい構造軸として合流させる。
+13. **Phase 56-OWNERSHIP-RELAY-DESIGN（完了✅ 2025-12-12）**: Ownership-Relay アーキテクチャ設計 + インターフェース skeleton
+   - 設計詳細: [phase56-ownership-relay-design.md](docs/development/current/main/phase56-ownership-relay-design.md)
+   - コア定義: owned / carriers / captures / relay の 4 分類を明確化
+   - 不変条件: Ownership Uniqueness / Carrier Locality / Relay Propagation / Capture Read-Only
+   - Module 作成: `src/mir/join_ir/ownership/` - 責務は「解析のみ」
+   - 型定義: `ScopeId`, `ScopeOwnedVar`, `RelayVar`, `CapturedVar`, `OwnershipPlan`
+   - テスト: 3 つのユニットテスト追加（empty plan / carriers filter / invariant verification）
+   - 次: Phase 57 で OwnershipAnalyzer 実装（dev-only）
+14. **Phase 57-OWNERSHIP-ANALYZER-DEV（次のフォーカス候補・dev-only）**: OwnershipPlan を生成する解析箱の実装
+   - `OwnershipAnalyzer` を追加し、ネスト含む reads/writes/owned を集計→ carriers/relay/captures を plan 化。
+   - 既存 fixtures（pattern2/3, jsonparser, selfhost）で plan の回帰テストを追加。
+15. JoinIR Verify / 最適化まわり
    - すでに PHI/ValueId 契約は debug ビルドで検証しているので、
      必要なら SSA‑DFA や軽い最適化（Loop invariant / Strength reduction）を検討。
 
diff --git a/docs/development/current/main/phase56-ownership-relay-design.md b/docs/development/current/main/phase56-ownership-relay-design.md
new file mode 100644
index 00000000..3797a620
--- /dev/null
+++ b/docs/development/current/main/phase56-ownership-relay-design.md
@@ -0,0 +1,224 @@
+# Phase 56: Ownership-Relay Design
+
+## Overview
+「読むのは自由、管理は直下 owned だけ」アーキテクチャの設計文書。
+
+Phase 56 は **インターフェース設計のみ**。実装は Phase 57 以降。
+
+## Core Definitions
+
+### owned (所有)
+- 変数を定義したスコープが唯一の owner
+- Loop直下の `local x` → そのループが owned
+- body-local（if/block内の local）→ 最も内側の enclosing loop が owned
+
+**例**:
+```rust
+fn outer() {
+    local a = 0    // owned by outer
+    loop {
+        local b = 0    // owned by this loop
+        if cond {
+            local c = 0    // owned by enclosing loop (not if!)
+        }
+    }
+}
+```
+
+### carriers (管理対象)
+- `carriers = writes ∩ owned`
+- そのスコープが定義 AND 更新する変数のみ
+- loop_step の引数として管理
+
+**重要**: Carrier は「所有 AND 更新」のみ。読み取り専用の owned 変数は carrier ではない。
+
+### captures (読み取り参照)
+- `captures = reads \ owned` (かつ carriers ではない)
+- 祖先スコープの変数への read-only アクセス
+- CapturedEnv / ConditionEnv 経由
+
+**例**:
+```rust
+local limit = 100
+loop {
+    local sum = 0
+    if sum < limit {  // limit は capture (read-only)
+        sum++         // sum は carrier (owned + written)
+    }
+}
+```
+
+### relay (中継)
+- 内側スコープが祖先 owned を更新する場合
+- 更新責務を owner へ昇格（relay up）
+- 中間ループは引数として素通し
+
+**例**:
+```rust
+loop outer {
+    local total = 0    // owned by outer
+    loop inner {
+        total++        // relay to outer (inner doesn't own total)
+    }
+}
+// outer の exit PHI で total を merge
+```
+
+## Invariants (不変条件)
+
+1. **Ownership Uniqueness**: 各変数は唯一の owner を持つ
+2. **Carrier Locality**: carriers = writes ∩ owned (借用なし)
+3. **Relay Propagation**: writes \ owned → owner に昇格
+4. **Capture Read-Only**: captures は read-only (PHI 不要)
+
+## Shadowing Rules
+
+```nyash
+local x = 0          // outer owned
+loop {
+    local x = 1      // inner owned (shadows outer)
+    // 外の x は capture 可能だが、inner の x が優先
+    print(x)         // inner の x (1)
+}
+print(x)             // outer の x (0)
+```
+
+- Shadowing = 新しい ownership 発生
+- 名前解決は最内スコープ優先
+- 外の x は capture として参照可能だが、内の x が存在する限り内が優先
+
+## Multi-Writer Merge
+
+```nyash
+loop outer {
+    local total = 0
+    if a { loop inner1 { total++ } }  // relay to outer
+    if b { loop inner2 { total-- } }  // relay to outer
+}
+// outer の exit PHI で merge
+```
+
+- Relay は「更新意図の伝達」
+- 実際の PHI merge は owner 側で実行
+- 複数の内側ループが同じ変数を relay → owner の exit PHI で統合
+
+## JoinIR Mapping
+
+### Current System → New System
+
+| Current | New |
+|---------|-----|
+| CarrierInfo.carriers | OwnershipPlan.owned_carriers |
+| promoted_loopbodylocals | (absorbed into owned analysis) |
+| CapturedEnv | OwnershipPlan.captures |
+| ConditionEnv | OwnershipPlan.condition_captures |
+| (implicit) | OwnershipPlan.relay_writes |
+
+### OwnershipPlan Structure
+
+```rust
+pub struct OwnershipPlan {
+    pub scope_id: ScopeId,
+    pub owned_carriers: Vec<ScopeOwnedVar>,
+    pub relay_writes: Vec<RelayVar>,
+    pub captures: Vec<CapturedVar>,
+    pub condition_captures: Vec<CapturedVar>,
+}
+```
+
+**設計意図**:
+- `owned_carriers`: このスコープが所有 AND 更新する変数
+- `relay_writes`: 祖先の変数への書き込み（owner へ昇格）
+- `captures`: 祖先の変数への読み取り専用参照
+- `condition_captures`: captures のうち、条件式で使われるもの
+
+## Implementation Phases
+
+- **Phase 56**: Design + interface skeleton (this phase) ✅
+- **Phase 57**: OwnershipAnalyzer implementation (dev-only)
+- **Phase 58**: P2 plumbing (dev-only)
+- **Phase 59**: P3 plumbing (dev-only)
+- **Phase 60**: Cleanup dev heuristics
+- **Phase 61**: Canonical promotion decision
+
+## Module Boundary
+
+`src/mir/join_ir/ownership/` - 責務は「解析のみ」
+
+**This module does**:
+- ✅ Collect reads/writes from AST/ProgramJSON
+- ✅ Determine variable ownership (owned/relay/capture)
+- ✅ Produce OwnershipPlan for downstream lowering
+
+**This module does NOT**:
+- ❌ Generate MIR instructions
+- ❌ Modify JoinIR structures
+- ❌ Perform lowering transformations
+
+Lowering/MIR生成は既存モジュールが担当。
+
+## Example Ownership Plans
+
+### Example 1: Simple Loop
+
+```nyash
+local sum = 0
+loop {
+    sum++
+}
+```
+
+**OwnershipPlan (loop scope)**:
+- `owned_carriers`: [`sum` (written)]
+- `relay_writes`: []
+- `captures`: []
+
+### Example 2: Nested Loop with Relay
+
+```nyash
+local total = 0
+loop outer {
+    loop inner {
+        total++
+    }
+}
+```
+
+**OwnershipPlan (inner loop)**:
+- `owned_carriers`: []
+- `relay_writes`: [`total` → relay to outer]
+- `captures`: []
+
+**OwnershipPlan (outer loop)**:
+- `owned_carriers`: [`total` (written via relay)]
+- `relay_writes`: []
+- `captures`: []
+
+### Example 3: Capture + Carrier
+
+```nyash
+local limit = 100
+loop {
+    local sum = 0
+    if sum < limit {
+        sum++
+    }
+}
+```
+
+**OwnershipPlan (loop scope)**:
+- `owned_carriers`: [`sum` (written)]
+- `relay_writes`: []
+- `captures`: [`limit` (read-only)]
+- `condition_captures`: [`limit`]
+
+## References
+- **Phase 53-54**: Structural axis expansion
+- **Phase 43/245B**: Normalized JoinIR completion
+- **ChatGPT discussion**: 「読むのは自由、管理は直下だけ」設計
+- **JoinIR Architecture**: [joinir-architecture-overview.md](joinir-architecture-overview.md)
+
+## Status
+
+- ✅ Phase 56 (this): Design + interface skeleton completed
+- ⏳ Phase 57+: Implementation pending
diff --git a/src/mir/join_ir/mod.rs b/src/mir/join_ir/mod.rs
index 2ddb3d56..43fb9449 100644
--- a/src/mir/join_ir/mod.rs
+++ b/src/mir/join_ir/mod.rs
@@ -41,6 +41,9 @@ pub mod normalized;
 // Phase 34-1: Frontend (AST→JoinIR) — skeleton only
 pub mod frontend;
 
+// Phase 56: Ownership analysis (reads/writes → owned/relay/capture)
+pub mod ownership;
+
 // Re-export lowering functions for backward compatibility
 pub use lowering::{
     lower_funcscanner_trim_to_joinir, lower_min_loop_to_joinir, lower_skip_ws_to_joinir,
diff --git a/src/mir/join_ir/ownership/README.md b/src/mir/join_ir/ownership/README.md
new file mode 100644
index 00000000..fd609e4f
--- /dev/null
+++ b/src/mir/join_ir/ownership/README.md
@@ -0,0 +1,79 @@
+# Ownership Analysis Module
+
+## Responsibility Boundary
+
+This module is responsible for **analysis only**:
+- ✅ Collecting reads/writes from AST/ProgramJSON
+- ✅ Determining variable ownership (owned/relay/capture)
+- ✅ Producing OwnershipPlan for downstream lowering
+
+This module does NOT:
+- ❌ Generate MIR instructions
+- ❌ Modify JoinIR structures
+- ❌ Perform lowering transformations
+
+## Core Types
+
+| Type | Purpose |
+|------|---------|
+| `ScopeId` | Unique scope identifier |
+| `ScopeOwnedVar` | Variable defined in this scope |
+| `RelayVar` | Write to ancestor-owned variable |
+| `CapturedVar` | Read-only reference to ancestor |
+| `OwnershipPlan` | Complete analysis result |
+
+## Invariants
+
+1. `carriers = owned_vars.filter(is_written)`
+2. No variable in both owned and relay
+3. No variable in both owned and captures
+4. Relay implies ancestor ownership exists
+
+## Design Philosophy
+
+**「読むのは自由、管理は直下 owned だけ」**
+
+- **Owned**: Variable defined in this scope (unique owner)
+- **Carrier**: Owned AND written (managed as loop_step argument)
+- **Capture**: Read-only reference to ancestor (via CapturedEnv)
+- **Relay**: Write to ancestor → relay up to owner (exit PHI at owner)
+
+## Phase Status
+
+- Phase 56: ✅ Interface skeleton
+- Phase 57: ⏳ OwnershipAnalyzer implementation
+- Phase 58: ⏳ P2 plumbing
+- Phase 59: ⏳ P3 plumbing
+- Phase 60: ⏳ Cleanup dev heuristics
+- Phase 61: ⏳ Canonical promotion decision
+
+## Usage (Future)
+
+```rust
+let plan = OwnershipAnalyzer::analyze(&ast_node, parent_scope);
+plan.verify_invariants()?;
+let carriers: Vec<_> = plan.carriers().collect();
+```
+
+## Example
+
+```nyash
+local limit = 100      // owned by outer
+loop {
+    local sum = 0      // owned by loop
+    if sum < limit {   // limit = capture (read-only)
+        sum++          // sum = carrier (owned + written)
+    }
+}
+```
+
+**OwnershipPlan (loop scope)**:
+- `owned_vars`: [`sum` (written), `limit` (read-only)]
+- `relay_writes`: []
+- `captures`: [`limit`]
+- `condition_captures`: [`limit`]
+
+## References
+
+- Design Doc: [phase56-ownership-relay-design.md](../../../../docs/development/current/main/phase56-ownership-relay-design.md)
+- JoinIR Architecture: [joinir-architecture-overview.md](../../../../docs/development/current/main/joinir-architecture-overview.md)
diff --git a/src/mir/join_ir/ownership/mod.rs b/src/mir/join_ir/ownership/mod.rs
new file mode 100644
index 00000000..0c65ec81
--- /dev/null
+++ b/src/mir/join_ir/ownership/mod.rs
@@ -0,0 +1,28 @@
+//! Ownership Analysis for JoinIR
+//!
+//! # Responsibility Boundary
+//!
+//! This module is responsible for **analysis only**:
+//! - Collecting reads/writes from AST/ProgramJSON
+//! - Determining variable ownership (owned/relay/capture)
+//! - Producing OwnershipPlan for downstream lowering
+//!
+//! This module does NOT:
+//! - Generate MIR instructions
+//! - Modify JoinIR structures
+//! - Perform lowering transformations
+//!
+//! # Core Invariants
+//!
+//! 1. **Ownership Uniqueness**: Each variable has exactly one owner scope
+//! 2. **Carrier Locality**: carriers = writes ∩ owned
+//! 3. **Relay Propagation**: writes to ancestor-owned → relay up
+//! 4. **Capture Read-Only**: captures have no PHI at this scope
+//!
+//! # Phase 56 Status
+//!
+//! Interface skeleton only. Implementation in Phase 57+.
+
+mod types;
+
+pub use types::*;
diff --git a/src/mir/join_ir/ownership/types.rs b/src/mir/join_ir/ownership/types.rs
new file mode 100644
index 00000000..adfed160
--- /dev/null
+++ b/src/mir/join_ir/ownership/types.rs
@@ -0,0 +1,168 @@
+//! Core types for ownership analysis.
+//!
+//! Phase 56: Interface definitions only (not yet used).
+
+#[cfg(any(debug_assertions, test))]
+use std::collections::BTreeSet;
+
+/// Unique identifier for a scope (loop, function, block).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct ScopeId(pub u32);
+
+/// A variable owned by the current scope.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ScopeOwnedVar {
+    /// Variable name
+    pub name: String,
+    /// Whether this variable is written within the scope
+    pub is_written: bool,
+    /// Whether this variable is used in loop conditions
+    pub is_condition_only: bool,
+}
+
+/// A variable whose updates should be relayed to an ancestor owner.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RelayVar {
+    /// Variable name
+    pub name: String,
+    /// Scope that owns this variable
+    pub owner_scope: ScopeId,
+    /// Intermediate scopes that need to forward this update
+    pub relay_path: Vec<ScopeId>,
+}
+
+/// A variable captured (read-only) from an ancestor scope.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CapturedVar {
+    /// Variable name
+    pub name: String,
+    /// Scope that owns this variable
+    pub owner_scope: ScopeId,
+}
+
+/// Complete ownership analysis result for a scope.
+#[derive(Debug, Clone, Default)]
+pub struct OwnershipPlan {
+    /// ID of this scope
+    pub scope_id: ScopeId,
+
+    /// Variables owned by this scope (defined here)
+    /// Invariant: carriers = owned_vars where is_written = true
+    pub owned_vars: Vec<ScopeOwnedVar>,
+
+    /// Variables written but owned by ancestor (need relay)
+    pub relay_writes: Vec<RelayVar>,
+
+    /// Variables read but not owned (read-only capture)
+    pub captures: Vec<CapturedVar>,
+
+    /// Subset of captures used in conditions
+    pub condition_captures: Vec<CapturedVar>,
+}
+
+impl Default for ScopeId {
+    fn default() -> Self {
+        ScopeId(0)
+    }
+}
+
+impl OwnershipPlan {
+    /// Create empty plan for a scope.
+    pub fn new(scope_id: ScopeId) -> Self {
+        Self {
+            scope_id,
+            ..Default::default()
+        }
+    }
+
+    /// Get carriers (owned AND written).
+    pub fn carriers(&self) -> impl Iterator<Item = &ScopeOwnedVar> {
+        self.owned_vars.iter().filter(|v| v.is_written)
+    }
+
+    /// Get condition-only carriers (owned, written, condition-only).
+    pub fn condition_only_carriers(&self) -> impl Iterator<Item = &ScopeOwnedVar> {
+        self.owned_vars.iter().filter(|v| v.is_written && v.is_condition_only)
+    }
+
+    /// Check invariant: no variable appears in multiple categories.
+    #[cfg(any(debug_assertions, test))]
+    pub fn verify_invariants(&self) -> Result<(), String> {
+        let mut all_names: BTreeSet<&str> = BTreeSet::new();
+
+        for v in &self.owned_vars {
+            if !all_names.insert(&v.name) {
+                return Err(format!("Duplicate owned var: {}", v.name));
+            }
+        }
+
+        for v in &self.relay_writes {
+            if self.owned_vars.iter().any(|o| o.name == v.name) {
+                return Err(format!("Relay var '{}' conflicts with owned", v.name));
+            }
+        }
+
+        for v in &self.captures {
+            if self.owned_vars.iter().any(|o| o.name == v.name) {
+                return Err(format!("Captured var '{}' conflicts with owned", v.name));
+            }
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_empty_plan() {
+        let plan = OwnershipPlan::new(ScopeId(1));
+        assert_eq!(plan.scope_id.0, 1);
+        assert!(plan.owned_vars.is_empty());
+        assert_eq!(plan.carriers().count(), 0);
+    }
+
+    #[test]
+    fn test_carriers_filter() {
+        let mut plan = OwnershipPlan::new(ScopeId(1));
+        plan.owned_vars.push(ScopeOwnedVar {
+            name: "sum".to_string(),
+            is_written: true,
+            is_condition_only: false,
+        });
+        plan.owned_vars.push(ScopeOwnedVar {
+            name: "limit".to_string(),
+            is_written: false,  // read-only owned
+            is_condition_only: false,
+        });
+
+        let carriers: Vec<_> = plan.carriers().collect();
+        assert_eq!(carriers.len(), 1);
+        assert_eq!(carriers[0].name, "sum");
+    }
+
+    #[test]
+    fn test_invariant_verification() {
+        let mut plan = OwnershipPlan::new(ScopeId(1));
+        plan.owned_vars.push(ScopeOwnedVar {
+            name: "x".to_string(),
+            is_written: true,
+            is_condition_only: false,
+        });
+
+        // Valid plan
+        assert!(plan.verify_invariants().is_ok());
+
+        // Add conflicting relay
+        plan.relay_writes.push(RelayVar {
+            name: "x".to_string(),
+            owner_scope: ScopeId(0),
+            relay_path: vec![],
+        });
+
+        // Now invalid
+        assert!(plan.verify_invariants().is_err());
+    }
+}