docs: output generated sources under docs/lib and docs/mcp

tests/cli/test_build_mkdocs.py

@@ -33,8 +33,6 @@ def test_mkdocs_build_full_flow(
                 "testpkg",
                 "--site-name",
                 "Test Site",
-                "--docs-dir",
-                "docs",
                 "--mkdocs-yml",
                 "mkdocs.yml",
             ],
@@ -43,7 +41,8 @@ def test_mkdocs_build_full_flow(
         assert result.exit_code == 0
         assert mock_mkdocs_build() is True
         assert (cwd / "mkdocs.yml").exists()
-        assert (cwd / "docs" / "testpkg" / "mod.md").exists()
+        assert (cwd / "docs" / "lib" / "testpkg" / "mod.md").exists()
+        assert "docs_dir: docs/lib" in (cwd / "mkdocs.yml").read_text()
 
 
 def test_mkdocs_build_missing_module_fails(cli_runner):
@@ -81,8 +80,6 @@ def test_mkdocs_build_without_site_name_uses_module_as_default_full_flow(
                 "--mkdocs",
                 "--module",
                 "testpkg",
-                "--docs-dir",
-                "docs",
                 "--mkdocs-yml",
                 "mkdocs.yml",
             ],
@@ -99,5 +96,5 @@ def test_mkdocs_build_without_site_name_uses_module_as_default_full_flow(
         content = mkdocs_yml.read_text()
         assert "site_name: testpkg" in content
 
-        # Docs must be generated
-        assert (cwd / "docs" / "testpkg" / "mod.md").exists()
+        # Docs must be generated under the nested docs/lib dir
+        assert (cwd / "docs" / "lib" / "testpkg" / "mod.md").exists()