diff --git a/builders/server/tests/core/runtime/test_real_scripts.py b/builders/server/tests/core/runtime/test_real_scripts.py
new file mode 100644
index 0000000..3f5416d
--- /dev/null
+++ b/builders/server/tests/core/runtime/test_real_scripts.py
@@ -0,0 +1,76 @@
+"""Validate the real builders/scripts directory, not fixtures.
+
+These tests gate dataset PRs (including ones opened by the dataset-creation
+flow): green CI means every committed config passes the same validation the
+server runs at startup, so a merged dataset cannot break boot.
+"""
+
+import ast
+import tomllib
+from pathlib import Path
+
+import core.runtime.registry as registry
+import pytest
+
+# builders/server/tests/core/runtime/ -> builders/scripts
+REAL_SCRIPTS_DIR = Path(__file__).resolve().parents[4] / "scripts"
+
+VERSION_DIRS = sorted(
+    (path.parent for path in REAL_SCRIPTS_DIR.glob("*/*/config.toml")),
+    key=str,
+)
+
+
+@pytest.fixture(autouse=True)
+def _reset_registry():
+    """reset _CONFIG_REGISTRY between tests."""
+    registry._CONFIG_REGISTRY = {}
+    yield
+    registry._CONFIG_REGISTRY = {}
+
+
+def _version_dir_id(version_dir: Path) -> str:
+    return f"{version_dir.parent.name}/{version_dir.name}"
+
+
+def test_scripts_dir_exists() -> None:
+    """the repo layout puts real builder scripts at builders/scripts."""
+    assert REAL_SCRIPTS_DIR.is_dir(), f"{REAL_SCRIPTS_DIR} not found"
+    assert VERSION_DIRS, "no config.toml found under builders/scripts"
+
+
+def test_all_real_configs_load_and_validate() -> None:
+    """every committed config passes the full startup validation
+
+    (structure, deps exist, no cycles, granularity, start dates).
+    """
+    registry.load_all_configs(REAL_SCRIPTS_DIR)
+    assert len(registry._CONFIG_REGISTRY) == len(VERSION_DIRS)
+
+
+@pytest.mark.parametrize("version_dir", VERSION_DIRS, ids=_version_dir_id)
+def test_builder_script_defines_build(version_dir: Path) -> None:
+    """each builder script exists, parses, and defines a top-level
+
+    build(dependencies, timestamp). ast-only so builder deps are never
+    imported.
+    """
+    with open(version_dir / "config.toml", "rb") as f:
+        raw = tomllib.load(f)
+    builder_path = version_dir / raw.get("builder", "builder.py")
+    assert builder_path.is_file(), f"{builder_path} missing"
+
+    tree = ast.parse(builder_path.read_text(), filename=str(builder_path))
+    build_fns = [
+        node
+        for node in tree.body
+        if isinstance(node, ast.FunctionDef) and node.name == "build"
+    ]
+    assert build_fns, f"{builder_path} has no top-level build()"
+
+    args = build_fns[0].args
+    positional = args.posonlyargs + args.args
+    assert len(positional) == 2, (
+        f"{builder_path} build() must take (dependencies, timestamp), "
+        f"got {[a.arg for a in positional]}"
+    )