feat(joinir): Phase 89 P1 - ContinueReturn lowering implementation

## ContinueReturn 独立箱
- continue_return_pattern.rs (457行)
- Continue + Early Return の JoinIR lowering
- StepCalculator 再利用（3箇所）
- Fail-Fast 原則徹底（5箇所検証）

## Dispatcher 配線
- mod.rs: LoopPattern::ContinueReturn 対応
- allowlist: pattern_continue_return_minimal 追加

## Fixture & Tests
- fixtures.rs: build_pattern_continue_return_min
- shapes.rs: +2 tests (vm_bridge + 期待値 n=10→acc=4)

Impact:
- normalized_dev: 61 passed (+2)
- lib tests: 993 passed (回帰なし)
- 箱化原則：単一責任・境界明確・再利用性高

Next: Phase 90 - _parse_string 合成 fixture

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/mir/join_ir/frontend/ast_lowerer/loop_patterns/continue_return_pattern.rs

@@ -0,0 +1,457 @@
+//! Phase 89 P1: ContinueReturn パターン lowering
+//!
+//! ## 責務（1行で表現）
+//! **continue + early return 両方を持つループを複合処理で JoinIR に落とす**
+//!
+//! ## パターン例
+//! ```nyash
+//! loop(i < n) {
+//!     if i == 5 { return acc }  // Early return
+//!     if i == 2 {
+//!         i = i + 1
+//!         continue
+//!     }
+//!     acc = acc + 1
+//!     i = i + 1
+//! }
+//! ```
+//!
+//! ## 生成する JoinIR 構造
+//! - entry 関数: Call(loop_step)
+//! - loop_step 関数:
+//!   - exit 条件チェック (i >= n で k_exit)
+//!   - early return 条件チェック (i == 5 で Jump(k_exit, acc))
+//!   - continue 条件チェック
+//!   - Select: continue なら acc そのまま、そうでなければ更新
+//!   - Select: continue なら i 追加更新、そうでなければ通常更新
+//!   - 再帰
+//! - k_exit 関数: Return(acc)
+//!
+//! ## 設計原則
+//! - **StepCalculator 再利用**: Phase 89-2 の成果活用
+//! - **Fail-Fast**: 複数 Return/Continue、Return が then 以外などは明示エラー
+//! - **境界明確**: continue_pattern.rs の設計を継承
+
+use super::common::{
+    build_join_module, create_k_exit_function, create_loop_context, parse_program_json,
+    process_local_inits,
+};
+use super::step_calculator::StepCalculator;
+use super::{AstToJoinIrLowerer, JoinModule, LoweringError};
+use crate::mir::join_ir::{CompareOp, ConstValue, JoinFunction, JoinInst, MirLikeInst};
+use crate::mir::ValueId;
+
+/// ContinueReturn パターンを JoinModule に変換
+///
+/// # Arguments
+/// * `lowerer` - AstToJoinIrLowerer インスタンス
+/// * `program_json` - Program(JSON v0)
+pub fn lower(
+    lowerer: &mut AstToJoinIrLowerer,
+    program_json: &serde_json::Value,
+) -> Result<JoinModule, LoweringError> {
+    // 1. Program(JSON) をパース
+    let parsed = parse_program_json(program_json);
+
+    // 2. LoopContext と entry_ctx を作成
+    let (ctx, mut entry_ctx) = create_loop_context(lowerer, &parsed);
+
+    // 3. Local 初期化を処理
+    let init_insts = process_local_inits(lowerer, &parsed, &mut entry_ctx);
+
+    // 4. Loop の cond を取得
+    let loop_node = &parsed.stmts[parsed.loop_node_idx];
+    let loop_cond_expr = &loop_node["cond"];
+
+    // 5. Loop body から Return If と Continue If を探す
+    let loop_body = loop_node["body"]
+        .as_array()
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Loop must have 'body' array".to_string(),
+        })?;
+
+    // 5-1. Return If を探す（Fail-Fast: 複数あればエラー）
+    let return_if_stmts: Vec<_> = loop_body
+        .iter()
+        .filter(|stmt| {
+            stmt["type"].as_str() == Some("If")
+                && stmt["then"].as_array().map_or(false, |then| {
+                    then.iter().any(|s| s["type"].as_str() == Some("Return"))
+                })
+        })
+        .collect();
+
+    if return_if_stmts.is_empty() {
+        return Err(LoweringError::InvalidLoopBody {
+            message: "ContinueReturn pattern must have If + Return".to_string(),
+        });
+    }
+
+    if return_if_stmts.len() > 1 {
+        return Err(LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: multiple Return statements found.\n\
+                 Expected: Exactly one 'if {{ return ... }}' statement in loop body.\n\
+                 Found: {} Return statements.\n\
+                 Hint: Combine multiple return conditions into a single if statement.",
+                return_if_stmts.len()
+            ),
+        });
+    }
+
+    let return_if_stmt = return_if_stmts[0];
+
+    // 5-2. Return が then にあることを確認（Fail-Fast）
+    let return_then = return_if_stmt["then"]
+        .as_array()
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Return If must have 'then' array".to_string(),
+        })?;
+
+    let return_stmt = return_then
+        .iter()
+        .find(|s| s["type"].as_str() == Some("Return"))
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Return If 'then' must contain Return statement".to_string(),
+        })?;
+
+    // else に Return があったら Fail-Fast
+    if let Some(else_branch) = return_if_stmt["else"].as_array() {
+        if else_branch
+            .iter()
+            .any(|s| s["type"].as_str() == Some("Return"))
+        {
+            return Err(LoweringError::InvalidLoopBody {
+                message: "ContinueReturn pattern validation failed: Return in 'else' branch.\n\
+                     Expected: Return statement only in 'then' branch.\n\
+                     Found: Return in 'else' branch.\n\
+                     Hint: Move Return statement to 'then' branch or invert condition."
+                    .to_string(),
+            });
+        }
+    }
+
+    let return_cond_expr = &return_if_stmt["cond"];
+    let return_expr = &return_stmt["expr"];
+
+    // 5-3. Continue If を探す（Fail-Fast: 複数あればエラー）
+    let continue_if_stmts: Vec<_> = loop_body
+        .iter()
+        .filter(|stmt| {
+            stmt["type"].as_str() == Some("If")
+                && stmt["then"].as_array().map_or(false, |then| {
+                    then.iter().any(|s| s["type"].as_str() == Some("Continue"))
+                })
+        })
+        .collect();
+
+    if continue_if_stmts.is_empty() {
+        return Err(LoweringError::InvalidLoopBody {
+            message: "ContinueReturn pattern must have If + Continue".to_string(),
+        });
+    }
+
+    if continue_if_stmts.len() > 1 {
+        return Err(LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: multiple Continue statements found.\n\
+                 Expected: Exactly one 'if {{ continue }}' statement in loop body.\n\
+                 Found: {} Continue statements.\n\
+                 Hint: Combine multiple continue conditions into a single if statement.",
+                continue_if_stmts.len()
+            ),
+        });
+    }
+
+    let continue_if_stmt = continue_if_stmts[0];
+    let continue_cond_expr = &continue_if_stmt["cond"];
+
+    // 6. entry 関数を生成
+    let entry_func =
+        create_entry_function_continue_return(&ctx, &parsed, init_insts, &mut entry_ctx);
+
+    // 7. loop_step 関数を生成
+    let loop_step_func = create_loop_step_function_continue_return(
+        lowerer,
+        &ctx,
+        &parsed.func_name,
+        loop_cond_expr,
+        return_cond_expr,
+        return_expr,
+        continue_cond_expr,
+        continue_if_stmt,
+        loop_body,
+    )?;
+
+    // 8. k_exit 関数を生成
+    let k_exit_func = create_k_exit_function(&ctx, &parsed.func_name);
+
+    // 9. JoinModule を構築
+    Ok(build_join_module(entry_func, loop_step_func, k_exit_func))
+}
+
+/// ContinueReturn パターン用 entry 関数を生成
+fn create_entry_function_continue_return(
+    ctx: &super::common::LoopContext,
+    parsed: &super::common::ParsedProgram,
+    init_insts: Vec<JoinInst>,
+    entry_ctx: &mut super::super::context::ExtractCtx,
+) -> JoinFunction {
+    // i, acc, n を取得
+    let i_init = entry_ctx.get_var("i").expect("i must be initialized");
+    let acc_init = entry_ctx.get_var("acc").expect("acc must be initialized");
+    let n_param = entry_ctx.get_var("n").expect("n must be parameter");
+
+    let loop_result = entry_ctx.alloc_var();
+
+    let mut body = init_insts;
+    body.push(JoinInst::Call {
+        func: ctx.loop_step_id,
+        args: vec![i_init, acc_init, n_param],
+        k_next: None,
+        dst: Some(loop_result),
+    });
+    body.push(JoinInst::Ret {
+        value: Some(loop_result),
+    });
+
+    JoinFunction {
+        id: ctx.entry_id,
+        name: parsed.func_name.clone(),
+        params: (0..parsed.param_names.len())
+            .map(|i| ValueId(i as u32))
+            .collect(),
+        body,
+        exit_cont: None,
+    }
+}
+
+/// ContinueReturn パターン用 loop_step 関数を生成
+#[allow(clippy::too_many_arguments)]
+fn create_loop_step_function_continue_return(
+    lowerer: &mut AstToJoinIrLowerer,
+    ctx: &super::common::LoopContext,
+    func_name: &str,
+    loop_cond_expr: &serde_json::Value,
+    return_cond_expr: &serde_json::Value,
+    return_expr: &serde_json::Value,
+    continue_cond_expr: &serde_json::Value,
+    continue_if_stmt: &serde_json::Value,
+    loop_body: &[serde_json::Value],
+) -> Result<JoinFunction, LoweringError> {
+    use super::super::context::ExtractCtx;
+
+    let step_i = ValueId(0);
+    let step_acc = ValueId(1);
+    let step_n = ValueId(2);
+
+    let mut step_ctx = ExtractCtx::new(3);
+    step_ctx.register_param("i".to_string(), step_i);
+    step_ctx.register_param("acc".to_string(), step_acc);
+    step_ctx.register_param("n".to_string(), step_n);
+
+    let mut body = Vec::new();
+
+    // 1. exit 条件チェック（!(i < n) = i >= n で抜ける）
+    let (cond_var, cond_insts) = lowerer.extract_value(loop_cond_expr, &mut step_ctx);
+    body.extend(cond_insts);
+
+    let false_const = step_ctx.alloc_var();
+    let exit_cond = step_ctx.alloc_var();
+
+    body.push(JoinInst::Compute(MirLikeInst::Const {
+        dst: false_const,
+        value: ConstValue::Bool(false),
+    }));
+    body.push(JoinInst::Compute(MirLikeInst::Compare {
+        dst: exit_cond,
+        op: CompareOp::Eq,
+        lhs: cond_var,
+        rhs: false_const,
+    }));
+
+    body.push(JoinInst::Jump {
+        cont: ctx.k_exit_id.as_cont(),
+        args: vec![step_acc],
+        cond: Some(exit_cond),
+    });
+
+    // 2. Early return 条件チェック（i == 5 で Jump(k_exit, return_val)）
+    let (return_cond_var, return_cond_insts) =
+        lowerer.extract_value(return_cond_expr, &mut step_ctx);
+    body.extend(return_cond_insts);
+
+    let (return_val, return_val_insts) = lowerer.extract_value(return_expr, &mut step_ctx);
+    body.extend(return_val_insts);
+
+    body.push(JoinInst::Jump {
+        cont: ctx.k_exit_id.as_cont(),
+        args: vec![return_val],
+        cond: Some(return_cond_var),
+    });
+
+    // 3. Continue pattern: i のインクリメント処理
+    // Continue If の then 内に i の更新がある場合、それを使う（例: i = i + 1）
+    let continue_then = continue_if_stmt["then"]
+        .as_array()
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Continue If must have 'then' array".to_string(),
+        })?;
+
+    let i_update_in_continue = continue_then
+        .iter()
+        .find(|stmt| stmt["type"].as_str() == Some("Local") && stmt["name"].as_str() == Some("i"))
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: missing 'i' increment in continue block.\n\
+                 Expected: Continue block must contain 'local i = i + K' where K is a constant.\n\
+                 Found: Continue block does not contain 'i' update.\n\
+                 Hint: Add 'i = i + 1' inside the 'if {{ continue }}' block."
+            ),
+        })?;
+
+    let i_expr = &i_update_in_continue["expr"];
+    let (i_next, i_insts) = lowerer.extract_value(i_expr, &mut step_ctx);
+    body.extend(i_insts);
+    step_ctx.register_param("i".to_string(), i_next);
+
+    // 通常の i 更新を探す（ループ末尾）
+    let i_update_normal = loop_body
+        .iter()
+        .filter(|stmt| stmt["type"].as_str() == Some("Local") && stmt["name"].as_str() == Some("i"))
+        .last() // Continue の後にある最後の i 更新を使う
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: missing normal 'i' increment.\n\
+                 Expected: Loop body must contain 'local i = i + K' outside continue block.\n\
+                 Found: No 'i' update found in loop body.\n\
+                 Hint: Add 'i = i + 1' at the end of the loop body."
+            ),
+        })?;
+
+    // Continue パスと通常パスの i 更新の差分計算（StepCalculator 活用）
+    let mut i_next_continue = i_next;
+    let base_k = StepCalculator::extract_linear_increment(&i_update_normal["expr"], "i")
+        .ok_or_else(|| {
+            let expr_debug = serde_json::to_string(&i_update_normal["expr"])
+                .unwrap_or_else(|_| "<invalid JSON>".to_string());
+            LoweringError::InvalidLoopBody {
+                message: format!(
+                    "ContinueReturn pattern validation failed: invalid step increment form.\n\
+                     Expected: i = i + const (e.g., 'i = i + 1', 'i = i + 2').\n\
+                     Found: {}\n\
+                     Hint: Change the 'i' update to addition form 'i = i + K' where K is a constant integer.",
+                    expr_debug
+                ),
+            }
+        })?;
+
+    let then_k = StepCalculator::extract_linear_increment(i_expr, "i").ok_or_else(|| {
+        let expr_debug =
+            serde_json::to_string(i_expr).unwrap_or_else(|_| "<invalid JSON>".to_string());
+        LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: invalid continue branch step increment.\n\
+                 Expected: In continue block, 'i = i + const' (e.g., 'i = i + 2').\n\
+                 Found: {}\n\
+                 Hint: Ensure the continue block updates 'i' using addition form 'i = i + K'.",
+                expr_debug
+            ),
+        }
+    })?;
+
+    let delta = StepCalculator::calculate_step_difference(then_k, base_k);
+    if delta != 0 {
+        let delta_const = step_ctx.alloc_var();
+        body.push(JoinInst::Compute(MirLikeInst::Const {
+            dst: delta_const,
+            value: ConstValue::Integer(delta),
+        }));
+        let bumped = step_ctx.alloc_var();
+        body.push(JoinInst::Compute(MirLikeInst::BinOp {
+            dst: bumped,
+            op: crate::mir::join_ir::BinOpKind::Add,
+            lhs: i_next,
+            rhs: delta_const,
+        }));
+        i_next_continue = bumped;
+    }
+
+    // 4. Continue 条件を評価
+    let (continue_cond_var, continue_cond_insts) =
+        lowerer.extract_value(continue_cond_expr, &mut step_ctx);
+    body.extend(continue_cond_insts);
+
+    // 5. acc の更新値を計算（通常パス）
+    let acc_update_local = loop_body
+        .iter()
+        .find(|stmt| {
+            stmt["type"].as_str() == Some("Local") && stmt["name"].as_str() == Some("acc")
+        })
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: format!(
+                "ContinueReturn pattern validation failed: missing accumulator update.\n\
+                 Expected: Loop body must contain 'local acc = ...' statement.\n\
+                 Found: No 'acc' update found in loop body.\n\
+                 Hint: Add 'acc = acc + <value>' or similar accumulator update."
+            ),
+        })?;
+
+    let acc_expr = &acc_update_local["expr"];
+    let (acc_increment, acc_insts) = lowerer.extract_value(acc_expr, &mut step_ctx);
+    body.extend(acc_insts);
+
+    // Continue 分岐側でも acc を更新できる場合（例: acc += 1）
+    let mut acc_then_val = step_acc;
+    if let Some(then_acc_local) = continue_then.iter().find(|stmt| {
+        stmt["type"].as_str() == Some("Local") && stmt["name"].as_str() == Some("acc")
+    }) {
+        let (acc_then, acc_then_insts) =
+            lowerer.extract_value(&then_acc_local["expr"], &mut step_ctx);
+        body.extend(acc_then_insts);
+        acc_then_val = acc_then;
+    }
+
+    // 6. Select: Continue/通常 で acc を切り替える
+    let acc_next = step_ctx.alloc_var();
+    body.push(JoinInst::Select {
+        dst: acc_next,
+        cond: continue_cond_var,
+        then_val: acc_then_val,
+        else_val: acc_increment,
+        type_hint: None,
+    });
+
+    // 7. Select: Continue/通常 で次 i を切り替える
+    // Note: 通常パスは i_next (continue の i 更新ベース)、continue パスは i_next_continue (差分加算済み)
+    // しかし、この fixture では continue 時に i = i + 1、通常時も i = i + 1 なので差分なし
+    // → 本実装では差分があっても動作するよう設計
+    let i_next_selected = step_ctx.alloc_var();
+    body.push(JoinInst::Select {
+        dst: i_next_selected,
+        cond: continue_cond_var,
+        then_val: i_next_continue,
+        else_val: i_next,
+        type_hint: None,
+    });
+
+    // 8. 末尾再帰
+    let recurse_result = step_ctx.alloc_var();
+    body.push(JoinInst::Call {
+        func: ctx.loop_step_id,
+        args: vec![i_next_selected, acc_next, step_n],
+        k_next: None,
+        dst: Some(recurse_result),
+    });
+    body.push(JoinInst::Ret {
+        value: Some(recurse_result),
+    });
+
+    Ok(JoinFunction {
+        id: ctx.loop_step_id,
+        name: format!("{}_loop_step", func_name),
+        params: vec![step_i, step_acc, step_n],
+        body,
+        exit_cont: None,
+    })
+}

src/mir/join_ir/frontend/ast_lowerer/loop_patterns/mod.rs

@@ -18,6 +18,7 @@ use super::{AstToJoinIrLowerer, JoinModule};
 pub mod break_pattern;
 pub mod common;
 pub mod continue_pattern;
+pub mod continue_return_pattern;
 pub mod filter;
 #[cfg(feature = "normalized_dev")]
 pub mod if_sum_break_pattern;
@@ -128,9 +129,6 @@ pub fn lower_loop_with_pattern(
         LoopPattern::Simple => simple::lower(lowerer, program_json),
         LoopPattern::Break => break_pattern::lower(lowerer, program_json),
         LoopPattern::Continue => continue_pattern::lower(lowerer, program_json),
-        LoopPattern::ContinueReturn => Err(LoweringError::UnimplementedPattern {
-            pattern: LoopPattern::ContinueReturn,
-            reason: "ContinueReturn pattern Phase 89 implementation in progress (Step 3)".to_string(),
-        }),
+        LoopPattern::ContinueReturn => continue_return_pattern::lower(lowerer, program_json),
     }
 }

src/mir/join_ir/frontend/ast_lowerer/mod.rs

@@ -94,6 +94,11 @@ fn resolve_function_route(func_name: &str) -> Result<FunctionRoute, String> {
             "jsonparser_unescape_string_step2_min",
             FunctionRoute::LoopFrontend,
         ),
+        // Phase 89 P1: ContinueReturn pattern minimal fixture
+        (
+            "pattern_continue_return_minimal",
+            FunctionRoute::LoopFrontend,
+        ),
     ];
 
     if let Some((_, route)) = TABLE.iter().find(|(name, _)| *name == func_name) {

src/mir/join_ir/normalized/fixtures.rs

@@ -823,6 +823,30 @@ pub fn build_jsonparser_unescape_string_step2_min_structured_for_normalized_dev(
     module
 }
 
+/// Pattern Continue + Return minimal を Structured で組み立てるヘルパー
+///
+/// Fixture: docs/private/roadmap2/phases/normalized_dev/fixtures/pattern_continue_return_min.program.json
+pub fn build_pattern_continue_return_min_structured_for_normalized_dev() -> JoinModule {
+    const FIXTURE: &str = include_str!(
+        "../../../../docs/private/roadmap2/phases/normalized_dev/fixtures/pattern_continue_return_min.program.json"
+    );
+
+    let program_json: serde_json::Value =
+        serde_json::from_str(FIXTURE).expect("pattern_continue_return_min fixture should be valid JSON");
+
+    let mut lowerer = AstToJoinIrLowerer::new();
+    let module = lowerer.lower_program_json(&program_json);
+
+    if joinir_dev_enabled() && joinir_test_debug_enabled() {
+        eprintln!(
+            "[joinir/normalized-dev] pattern_continue_return_min structured module: {:#?}",
+            module
+        );
+    }
+
+    module
+}
+
 /// まとめて import したいとき用のプレリュード。
 pub mod prelude {
     pub use super::{
@@ -839,6 +863,7 @@ pub mod prelude {
         build_pattern3_if_sum_multi_min_structured_for_normalized_dev,
         build_pattern3_json_if_sum_min_structured_for_normalized_dev,
         build_pattern4_continue_min_structured_for_normalized_dev,
+        build_pattern_continue_return_min_structured_for_normalized_dev,
         build_selfhost_if_sum_p3_ext_structured_for_normalized_dev,
         build_selfhost_if_sum_p3_structured_for_normalized_dev,
         build_selfhost_token_scan_p2_accum_structured_for_normalized_dev,