refactor(impact): CodeParser 多语言就绪——语言适配器注册表（仅 Java，行为不变）

- BaseLanguageParser 抽象基类 + JavaLanguageParser（迁移全部 Java 正则，输出逐字节一致）
- LANGUAGE_PARSERS 注册表 + register_language_parser 扩展点（新增语言=加适配器类并注册，下游零改动）
- CodeParser 分发器：parse(root, language=None) 自动按扩展名探测 / 显式语言覆盖 / 多语言合并（language 逗号连接）/ 无源码或语言不支持抛 CodeParseError
- source_aggregator 新增 existing_system_language 透传；config.py 探测扩展名补 .py/.ts/.go/.cs
- 删除自动探测下不可达死分支；全量 362 passed / 99.28%（基线 351/99.27%）
- 门禁复跑 PASS：summary 与 MVP 基线一致（16/5/8/3/50/0），概要设计书 13 章

tests/test_code_parser.py

@@ -1,9 +1,17 @@
-"""CodeParser 测试（Impact Agent MVP）：Java 项目解析 → CodeStructure。"""
+"""CodeParser 测试（Impact Agent MVP）：多语言适配器注册表 + Java 项目解析。"""
 from pathlib import Path
 
 import pytest
 
-from genesis.impact.code_parser import CodeParseError, CodeParser
+from genesis.data_models import ControllerInfo, EndpointInfo
+from genesis.impact.code_parser import (
+    LANGUAGE_PARSERS,
+    BaseLanguageParser,
+    CodeParseError,
+    CodeParser,
+    JavaLanguageParser,
+    register_language_parser,
+)
 
 FIXTURE_JAVA = {
     "trade-order/src/main/java/com/trade/order/controller/OrderController.java": (
@@ -124,3 +132,106 @@ def test_parse_real_sample_has_entities_and_endpoints():
     assert result.entities, "既有系统样本应至少有一个实体类"
     assert result.endpoints, "既有系统样本应至少有一个端点"
     assert result.services, "既有系统样本应至少有一个 @Service 类"
+
+
+# ---------- 多语言适配器注册表（预备性重构） ----------
+
+class _FakeParser(BaseLanguageParser):
+    """测试用假语言适配器：验证注册表/分发/多语言合并。"""
+
+    language = "fake"
+    extensions = (".fx",)
+
+    def parse_file(self, text: str, rel: str) -> dict:
+        return {
+            "imports": ["fake.import"],
+            "classes": [{"class_name": "FakeThing", "path": rel}],
+            "controllers": [
+                ControllerInfo(
+                    name="FakeThing", class_name="FakeThing", path=rel,
+                    base_path="/fake", endpoints=["/fake"], source_uri=rel,
+                )
+            ],
+            "services": [],
+            "entities": [],
+            "endpoints": [
+                EndpointInfo(
+                    method="GET", path="/fake", controller="FakeThing",
+                    description="", source_uri=rel,
+                )
+            ],
+        }
+
+
+def test_language_registry_contains_java():
+    assert "java" in LANGUAGE_PARSERS
+    assert issubclass(LANGUAGE_PARSERS["java"], BaseLanguageParser)
+
+
+def test_java_parser_adapter_metadata():
+    jp = JavaLanguageParser()
+    assert jp.language == "java"
+    assert ".java" in jp.extensions
+
+
+def test_base_parser_parse_file_contract():
+    with pytest.raises(NotImplementedError):
+        BaseLanguageParser().parse_file("text", "rel")
+
+
+def test_parse_explicit_language(tmp_path):
+    root = _make_project(tmp_path, FIXTURE_JAVA)
+    result = CodeParser().parse(root, language="java")
+    assert {c.class_name for c in result.controllers} == {"OrderController"}
+    assert result.language == "java"
+
+
+def test_parse_unsupported_language_raises(tmp_path):
+    root = _make_project(tmp_path, FIXTURE_JAVA)
+    with pytest.raises(CodeParseError):
+        CodeParser().parse(root, language="kotlin")
+
+
+def test_parse_explicit_language_no_files_raises(tmp_path):
+    (tmp_path / "readme.txt").write_text("hello", encoding="utf-8")
+    with pytest.raises(CodeParseError):
+        CodeParser().parse(tmp_path, language="java")
+
+
+def test_java_parse_file_interface(tmp_path):
+    jp = JavaLanguageParser()
+    text = FIXTURE_JAVA["trade-order/src/main/java/com/trade/order/controller/OrderController.java"]
+    out = jp.parse_file(text, "OrderController.java")
+    assert len(out["controllers"]) == 1
+    assert out["controllers"][0].class_name == "OrderController"
+    assert {"/api/order/{id}", "/api/order/create"} <= {e.path for e in out["endpoints"]}
+    assert out["classes"] == [{"class_name": "OrderController", "path": "OrderController.java"}]
+
+
+def test_register_and_dispatch_new_language(tmp_path):
+    register_language_parser("fake", _FakeParser)
+    try:
+        root = _make_project(tmp_path, {
+            "app/main.fx": "FAKE",
+            "trade-order/src/main/java/com/trade/order/controller/OrderController.java": (
+                FIXTURE_JAVA["trade-order/src/main/java/com/trade/order/controller/OrderController.java"]
+            ),
+        })
+        result = CodeParser().parse(root)
+        names = {c.class_name for c in result.controllers}
+        assert names == {"OrderController", "FakeThing"}
+        assert result.language == "fake,java"  # 多语言按名排序逗号连接
+        assert any(e.path == "/fake" for e in result.endpoints)
+    finally:
+        LANGUAGE_PARSERS.pop("fake", None)
+
+
+def test_register_language_explicit_only(tmp_path):
+    register_language_parser("fake", _FakeParser)
+    try:
+        root = _make_project(tmp_path, {"a/main.fx": "FAKE"})
+        result = CodeParser().parse(root, language="fake")
+        assert result.language == "fake"
+        assert [c.class_name for c in result.controllers] == ["FakeThing"]
+    finally:
+        LANGUAGE_PARSERS.pop("fake", None)