feat(joinir): Phase 49-3 JoinIR Frontend mainline integration

Implement AST→JSON→JoinIR→MIR pipeline in cf_loop for print_tokens:
- Add cf_loop_joinir_impl() with full pipeline:
  - AST Loop node → Program JSON
  - AstToJoinIrLowerer::lower_program_json() → JoinModule
  - convert_join_module_to_mir_with_meta() → MirModule
  - merge_joinir_mir_blocks() (MVP: logging only)

- Add Phase 49 smoke tests (2 tests):
  - phase49_joinir_mainline_pipeline_smoke
  - phase49_joinir_mainline_fallback_without_flag

- Dev flag: HAKO_JOINIR_PRINT_TOKENS_MAIN=1
- Debug flag: NYASH_JOINIR_MAINLINE_DEBUG=1

MVP limitations:
- Block merge is logging only (Phase 49-3.2 for full impl)
- if-analysis meta is empty (Phase 40+ territory)

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

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

src/tests/joinir/mainline_phase49.rs

@@ -0,0 +1,131 @@
+// Phase 49-3: JoinIR Frontend Mainline Integration Test
+//
+// このテストは cf_loop の JoinIR Frontend mainline route が
+// 正常に動作することを確認する。
+//
+// MVP 制限:
+// - merge_joinir_mir_blocks() はログ出力のみ
+// - 完全な A/B 比較は Phase 49-3.2（ブロックマージ実装）待ち
+//
+// テスト方法:
+// HAKO_JOINIR_PRINT_TOKENS_MAIN=1 cargo test --release joinir_mainline_phase49
+
+use crate::ast::ASTNode;
+use crate::mir::MirCompiler;
+use crate::parser::NyashParser;
+
+/// Phase 49-3: JoinIR Frontend mainline パイプラインが
+/// print_tokens 関数のコンパイル時にクラッシュしないことを確認
+#[test]
+fn phase49_joinir_mainline_pipeline_smoke() {
+    // Phase 49 mainline route は dev フラグで制御
+    std::env::set_var("HAKO_JOINIR_PRINT_TOKENS_MAIN", "1");
+    std::env::set_var("NYASH_JOINIR_MAINLINE_DEBUG", "1");
+    std::env::set_var("NYASH_PARSER_STAGE3", "1");
+    std::env::set_var("HAKO_PARSER_STAGE3", "1");
+    std::env::set_var("NYASH_DISABLE_PLUGINS", "1");
+
+    // print_tokens を含む最小限の JsonTokenizer 定義
+    let src = r#"
+box JsonTokenizer {
+    tokens: ArrayBox
+    errors: ArrayBox
+
+    birth() {
+        me.tokens = new ArrayBox()
+        me.errors = new ArrayBox()
+    }
+
+    // Phase 49 ターゲット関数
+    print_tokens() {
+        local i = 0
+        loop(i < me.tokens.length()) {
+            local token = me.tokens.get(i)
+            print(token)
+            i = i + 1
+        }
+    }
+}
+
+static box Main {
+    main() {
+        local t = new JsonTokenizer()
+        t.print_tokens()
+        return 0
+    }
+}
+"#;
+
+    let ast: ASTNode = NyashParser::parse_from_string(src)
+        .expect("phase49: parse failed");
+
+    let mut mc = MirCompiler::with_options(false);
+    let result = mc.compile(ast);
+
+    // MVP: パイプラインがクラッシュしないことを確認
+    // Phase 49-3.2 で実際の A/B 比較を追加
+    assert!(
+        result.is_ok(),
+        "phase49 mainline compile should not crash: {:?}",
+        result.err()
+    );
+
+    // クリーンアップ
+    std::env::remove_var("HAKO_JOINIR_PRINT_TOKENS_MAIN");
+    std::env::remove_var("NYASH_JOINIR_MAINLINE_DEBUG");
+    std::env::remove_var("NYASH_PARSER_STAGE3");
+    std::env::remove_var("HAKO_PARSER_STAGE3");
+    std::env::remove_var("NYASH_DISABLE_PLUGINS");
+}
+
+/// Phase 49-3: dev フラグ OFF 時は従来経路を使用することを確認
+#[test]
+fn phase49_joinir_mainline_fallback_without_flag() {
+    // dev フラグ OFF
+    std::env::remove_var("HAKO_JOINIR_PRINT_TOKENS_MAIN");
+    std::env::set_var("NYASH_PARSER_STAGE3", "1");
+    std::env::set_var("HAKO_PARSER_STAGE3", "1");
+    std::env::set_var("NYASH_DISABLE_PLUGINS", "1");
+
+    let src = r#"
+box JsonTokenizer {
+    tokens: ArrayBox
+
+    birth() {
+        me.tokens = new ArrayBox()
+    }
+
+    print_tokens() {
+        local i = 0
+        loop(i < me.tokens.length()) {
+            i = i + 1
+        }
+    }
+}
+
+static box Main {
+    main() {
+        local t = new JsonTokenizer()
+        t.print_tokens()
+        return 0
+    }
+}
+"#;
+
+    let ast: ASTNode = NyashParser::parse_from_string(src)
+        .expect("phase49 fallback: parse failed");
+
+    let mut mc = MirCompiler::with_options(false);
+    let result = mc.compile(ast);
+
+    assert!(
+        result.is_ok(),
+        "phase49 fallback compile should succeed: {:?}",
+        result.err()
+    );
+
+    // クリーンアップ
+    std::env::remove_var("NYASH_PARSER_STAGE3");
+    std::env::remove_var("HAKO_PARSER_STAGE3");
+    std::env::remove_var("NYASH_DISABLE_PLUGINS");
+}

src/tests/joinir/mod.rs

@@ -3,4 +3,5 @@ pub mod bridge;
 pub mod frontend;
 pub mod json;
 pub mod lowering;
+pub mod mainline_phase49; // Phase 49: JoinIR Frontend mainline integration
 pub mod runner;