diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 4c5dda3..5c1c62f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -42,6 +42,13 @@ uv run python scripts/run_actionlint.py
 when it is not cached. A passing static workflow check does not mean the
 workflow has run successfully on GitHub.
 
+Both Hatch build targets explicitly emit Core Metadata 2.4, which the locked
+Twine toolchain can validate. Build isolation resolves Hatchling separately from
+`uv.lock`, so relying on its default metadata version can break an unchanged
+checkout. The build regression test checks both the sdist-to-wheel path and a
+direct wheel build with the locked Twine validator. Change the metadata format
+only together with verified support in the validation and publication tools.
+
 If a check is unavailable, say so in the pull request rather than describing
 it as passing.
 
diff --git a/pyproject.toml b/pyproject.toml
index 49568cf..4359dff 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -51,6 +51,7 @@ requires = ["hatchling>=1.27.0,<2.0.0"]
 build-backend = "hatchling.build"
 
 [tool.hatch.build.targets.sdist]
+core-metadata-version = "2.4"
 include = [
     "/AGENTS.md",
     "/ARCHITECTURE.md",
@@ -71,6 +72,7 @@ include = [
 ]
 
 [tool.hatch.build.targets.wheel]
+core-metadata-version = "2.4"
 packages = ["src/cometapi"]
 
 [tool.pyright]
diff --git a/tests/test_release_documents.py b/tests/test_release_documents.py
index 590dc0b..b5d54ae 100644
--- a/tests/test_release_documents.py
+++ b/tests/test_release_documents.py
@@ -1576,6 +1576,30 @@ def test_artifact_metadata_accepts_publication_neutral_long_description() -> Non
     )
 
 
+@pytest.mark.parametrize("build_options", [[], ["--wheel"]], ids=["sdist-to-wheel", "direct-wheel"])
+def test_built_distributions_pass_locked_twine_check(
+    tmp_path: Path, build_options: list[str]
+) -> None:
+    """Exercise the isolated build backend against the locked metadata validator."""
+    built = tmp_path / "distributions"
+    subprocess.run(
+        ["uv", "build", *build_options, "--out-dir", str(built)],
+        cwd=PROJECT_ROOT,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+    artifacts = sorted(built.glob("*.whl")) + sorted(built.glob("*.tar.gz"))
+    assert len(artifacts) == (1 if build_options else 2)
+    subprocess.run(
+        [sys.executable, "-m", "twine", "check", "--strict", *map(str, artifacts)],
+        cwd=tmp_path,
+        check=True,
+        capture_output=True,
+        text=True,
+    )
+
+
 @pytest.mark.parametrize(
     "description",
     [