[moz] impl(§17): issue_assigned steps git 操作具体化 + ToolchainApiSection Git 说明

改动 1: issue_assigned 编码路径 steps 改为具体 git 命令
  (checkout main → pull → checkout -b → add/commit → push)
改动 2: ToolchainApiSection 新增 Git 操作说明段落（含开发目录路径）
改动 3: 测试更新（issue_assigned 断言 + 3 个 Git 说明测试）
466 passed

tests/unit/test_toolchain_handler_v2.py

@@ -563,7 +563,7 @@ class TestIssueAssignedLabelRouting:
     def test_normal_issue_keeps_coding_steps(self):
         source_file = PROJECT_ROOT / "src" / "api" / "toolchain_routes.py"
         source = source_file.read_text()
-        assert '创建分支 fix/' in source
+        assert 'git checkout -b fix/' in source
         assert 'issue_assigned' in source
 
 
@@ -593,3 +593,28 @@ class TestRedFlagsInfrastructure:
         source = source_file.read_text()
         assert "不是我代码的问题" in source
         assert "基础设施问题" in source
+
+
+class TestGitOperationGuidance:
+    """ToolchainApiSection should include Git operation guidance."""
+
+    def test_has_git_operation_section(self):
+        source_file = PROJECT_ROOT / "src" / "daemon" / "toolchain_handler.py"
+        source = source_file.read_text()
+        assert "Git 操作说明" in source
+        assert "git checkout main" in source
+        assert "git pull origin main" in source
+        assert "git checkout -b" in source
+
+    def test_has_no_main_commit_warning(self):
+        source_file = PROJECT_ROOT / "src" / "daemon" / "toolchain_handler.py"
+        source = source_file.read_text()
+        assert "不要在 main 分支上直接 commit" in source
+
+    def test_issue_assigned_steps_have_git_commands(self):
+        source_file = PROJECT_ROOT / "src" / "api" / "toolchain_routes.py"
+        source = source_file.read_text()
+        assert 'git checkout main && git pull origin main' in source
+        assert 'git checkout -b fix/' in source
+        assert 'git add -A && git commit' in source
+        assert 'git push origin fix/' in source