feat(joinir): Phase 88 - Pattern4 continue + variable step increment

Continue Pattern 拡張:
- then側の i=i+const 差分加算 + acc更新を許可
- continue_pattern.rs:193 で可変ステップ検出

Dev Router 許可:
- ast_lowerer/mod.rs:92 で normalized_dev feature時に新パターンを有効化

Fixtures & Tests:
- jsonparser_unescape_string_step2_min fixture追加（submodule）
- normalized_joinir_min.rs に shape テスト追加
- shapes.rs に expected shape 定義

Documentation:
- joinir-architecture-overview.md に Phase 88 到達点を追記

Impact:
- Pattern4 continue + 可変インクリメント（i+=1 or i+=2）対応
- _unescape_string 制御構造の土台確立
- normalized_dev tests PASS

Next: _unescape_string 残り複合ループ対応

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

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

docs/development/current/main/joinir-architecture-overview.md

@@ -833,6 +833,8 @@ Pattern2/4 への統合（実際に Body-local 更新を使うループを JoinI
     （P2 + P4 + P5 の組み合わせで表現可能なことを設計上確認済み）
 - 低優先度だが理論上は P1–P4 からの拡張で吸収可能:
   - `_unescape_string` など、複雑な continue / 条件付き更新を含むループ
+    - Phase 88（dev-only）で、`i+=2 + continue`（かつ continue 分岐側で `acc` 更新）を最小フィクスチャとして抽出し、
+      frontend の continue pattern を「`i = i + const` の差分加算」に限定して段階拡張した。
 
 方針:
 

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

@@ -83,6 +83,7 @@ pub fn lower(
         &parsed.func_name,
         loop_cond_expr,
         continue_cond_expr,
+        continue_if_stmt,
         loop_body,
     )?;
 
@@ -136,6 +137,7 @@ fn create_loop_step_function_continue(
     func_name: &str,
     loop_cond_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;
@@ -188,6 +190,67 @@ fn create_loop_step_function_continue(
     body.extend(i_insts);
     step_ctx.register_param("i".to_string(), i_next);
 
+    // Phase 88: Continue 分岐で i を追加更新できるようにする（例: i += 2）
+    //
+    // `continue_if` の then 内に `Local i = i + K` がある場合、
+    // loop_body の通常更新 `Local i = i + K0` との差分 (K-K0) を i_next に加算して
+    // continue パスの次 i を構成する（Linear increment のみ対応）。
+    fn extract_add_i_const(expr: &serde_json::Value) -> Option<i64> {
+        if expr["type"].as_str()? != "Binary" || expr["op"].as_str()? != "+" {
+            return None;
+        }
+        let lhs = &expr["lhs"];
+        let rhs = &expr["rhs"];
+        // i + const
+        if lhs["type"].as_str()? == "Var" && lhs["name"].as_str()? == "i" {
+            if rhs["type"].as_str()? == "Int" {
+                return rhs["value"].as_i64();
+            }
+        }
+        // const + i
+        if rhs["type"].as_str()? == "Var" && rhs["name"].as_str()? == "i" {
+            if lhs["type"].as_str()? == "Int" {
+                return lhs["value"].as_i64();
+            }
+        }
+        None
+    }
+
+    let mut i_next_continue = i_next;
+    let continue_then = continue_if_stmt["then"]
+        .as_array()
+        .ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Continue pattern If must have 'then' array".to_string(),
+        })?;
+    if let Some(then_i_local) = continue_then
+        .iter()
+        .find(|stmt| stmt["type"].as_str() == Some("Local") && stmt["name"].as_str() == Some("i"))
+    {
+        let base_k = extract_add_i_const(i_expr).ok_or_else(|| LoweringError::InvalidLoopBody {
+            message: "Continue pattern requires i update of form (i + const)".to_string(),
+        })?;
+        let then_k =
+            extract_add_i_const(&then_i_local["expr"]).ok_or_else(|| LoweringError::InvalidLoopBody {
+                message: "Continue pattern requires then i update of form (i + const)".to_string(),
+            })?;
+        let delta = 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;
+        }
+    }
+
     // 3. Continue 条件を評価
     let (continue_cond_var, continue_cond_insts) =
         lowerer.extract_value(continue_cond_expr, &mut step_ctx);
@@ -205,21 +268,41 @@ fn create_loop_step_function_continue(
     let (acc_increment, acc_insts) = lowerer.extract_value(acc_expr, &mut step_ctx);
     body.extend(acc_insts);
 
-    // 5. Select: Continue なら acc そのまま、そうでなければ更新
+    // Phase 88: Continue 分岐側でも acc を更新できるようにする（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;
+    }
+
+    // 5. 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: step_acc,      // Continue: 更新しない
+        then_val: acc_then_val,
-        else_val: acc_increment, // 通常: 更新
+        else_val: acc_increment,
         type_hint: None,         // Phase 63-3
     });
 
+    // Phase 88: Continue/通常 で次 i を切り替える
+    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,
+    });
+
     // 6. 末尾再帰
     let recurse_result = step_ctx.alloc_var();
     body.push(JoinInst::Call {
         func: ctx.loop_step_id,
-        args: vec![i_next, acc_next, step_n],
+        args: vec![i_next_selected, acc_next, step_n],
         k_next: None,
         dst: Some(recurse_result),
     });

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

@@ -89,6 +89,11 @@ fn resolve_function_route(func_name: &str) -> Result<FunctionRoute, String> {
             "jsonparser_parse_object_continue_skip_ws",
             FunctionRoute::LoopFrontend,
         ),
+        // Phase 88: JsonParser _unescape_string core (step2 + continue) minimal fixture
+        (
+            "jsonparser_unescape_string_step2_min",
+            FunctionRoute::LoopFrontend,
+        ),
     ];
 
     if let Some((_, route)) = TABLE.iter().find(|(name, _)| *name == func_name) {

src/mir/join_ir/normalized/fixtures.rs

@@ -796,6 +796,33 @@ pub fn build_jsonparser_parse_object_continue_skip_ws_structured_for_normalized_
     module
 }
 
+/// JsonParser _unescape_string の「i+=2 + continue」コアを Structured で組み立てるヘルパー（dev-only）。
+///
+/// 実ループ（`tools/hako_shared/json_parser.hako::_unescape_string`）から、
+/// 文字列処理を除いて制御構造（continue + 可変ステップ更新）だけを抽出した最小フィクスチャ。
+///
+/// Fixture: docs/private/roadmap2/phases/normalized_dev/fixtures/jsonparser_unescape_string_step2_min.program.json
+pub fn build_jsonparser_unescape_string_step2_min_structured_for_normalized_dev() -> JoinModule {
+    const FIXTURE: &str = include_str!(
+        "../../../../docs/private/roadmap2/phases/normalized_dev/fixtures/jsonparser_unescape_string_step2_min.program.json"
+    );
+
+    let program_json: serde_json::Value = serde_json::from_str(FIXTURE)
+        .expect("jsonparser_unescape_string_step2_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] jsonparser_unescape_string_step2_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::{
@@ -806,6 +833,7 @@ pub mod prelude {
         build_jsonparser_parse_object_continue_skip_ws_structured_for_normalized_dev,
         build_jsonparser_skip_ws_real_structured_for_normalized_dev,
         build_jsonparser_skip_ws_structured_for_normalized_dev,
+        build_jsonparser_unescape_string_step2_min_structured_for_normalized_dev,
         build_pattern2_break_fixture_structured, build_pattern2_minimal_structured,
         build_pattern3_if_sum_min_structured_for_normalized_dev,
         build_pattern3_if_sum_multi_min_structured_for_normalized_dev,

tests/normalized_joinir_min.rs

@@ -12,6 +12,7 @@ use nyash_rust::mir::join_ir::normalized::fixtures::{
     build_jsonparser_parse_object_continue_skip_ws_structured_for_normalized_dev,
     build_jsonparser_skip_ws_real_structured_for_normalized_dev,
     build_jsonparser_skip_ws_structured_for_normalized_dev,
+    build_jsonparser_unescape_string_step2_min_structured_for_normalized_dev,
     build_pattern2_break_fixture_structured, build_pattern2_minimal_structured,
     build_pattern3_if_sum_min_structured_for_normalized_dev,
     build_pattern3_if_sum_multi_min_structured_for_normalized_dev,

tests/normalized_joinir_min/shapes.rs

@@ -295,6 +295,24 @@ fn test_normalized_pattern4_jsonparser_parse_object_continue_skip_ws_vm_bridge_d
     }
 }
 
+/// Phase 88: JsonParser _unescape_string コア（i+=2 + continue）を canonical route で固定する。
+#[test]
+fn test_phase88_jsonparser_unescape_string_step2_min_canonical_matches_structured() {
+    let structured = build_jsonparser_unescape_string_step2_min_structured_for_normalized_dev();
+    let entry = structured.entry.expect("structured entry required");
+
+    // n=10 → i=0,2,4,6,8 で acc++ → 5
+    let args = [JoinValue::Int(10)];
+    let structured_res = run_joinir_vm_bridge_structured_only(&structured, entry, &args);
+    let canonical = run_joinir_vm_bridge(&structured, entry, &args, false);
+
+    assert_eq!(
+        structured_res, canonical,
+        "canonical unescape(step2) mismatch"
+    );
+    assert_eq!(canonical, JoinValue::Int(5));
+}
+
 /// Phase 48-C: JsonParser _parse_object continue skip_ws canonical route should match Structured
 #[test]
 fn test_normalized_pattern4_jsonparser_parse_object_continue_skip_ws_canonical_matches_structured()