diff --git a/behavision/cameras.py b/behavision/cameras.py
index 289d428..78bbf5b 100644
--- a/behavision/cameras.py
+++ b/behavision/cameras.py
@@ -182,13 +182,22 @@ class CameraStore:
 
         After that the store is authoritative — otherwise a camera the user
         deleted in the UI would reappear on every restart.
+
+        Entries with no address are dropped rather than imported. The bundled
+        config declares one whose host comes from the environment, which is
+        right for a checkout with a .env and resolves to nothing on every
+        machine the product is actually installed on. Seeding that would put a
+        camera the shop never added into a brand new install, permanently
+        failing to connect to "" — and the first thing they would have to do is
+        work out what it was and delete it.
         """
         with self._lock:
-            if self.path.exists() or not cameras:
+            usable = [c for c in cameras if c.addressed()]
+            if self.path.exists() or not usable:
                 return False
-            for cam in cameras:
+            for cam in usable:
                 self._cameras[cam.id] = cam
             self._save()
             log.info("seeded %d camera(s) from YAML into %s",
-                     len(cameras), self.path)
+                     len(usable), self.path)
             return True
diff --git a/behavision/config.py b/behavision/config.py
index bb944b3..19b09be 100644
--- a/behavision/config.py
+++ b/behavision/config.py
@@ -55,6 +55,43 @@ class CameraConfig(BaseModel):
     max_width: int = 1280  # frames wider than this are downscaled at ingest
     tuning: CameraTuning = CameraTuning()
 
+    @model_validator(mode="before")
+    @classmethod
+    def _normalize_blanks(cls, values):
+        # Unset ${ENV} placeholders parse as YAML null, not "" - the same trap
+        # ApiSection and EmailSection already guard against, and this section
+        # did not. The bundled config/default.yaml reads its camera's host,
+        # username and password from the environment, so on any machine
+        # WITHOUT a .env - which is every machine the product is installed on -
+        # loading it raised three pydantic errors and the engine would not
+        # start at all. Found by cloning the repository and running the tests.
+        if not isinstance(values, dict):
+            return values
+        # Named fields only, never a blanket None -> "". `webcam` is an
+        # Optional[int] whose None is meaningful ("this is not a webcam"), and
+        # `tuning` is a nested model; sweeping either into "" trades one
+        # validation error for another.
+        values = dict(values)
+        for key in ("url", "host", "path", "username", "password"):
+            if values.get(key) is None:
+                values[key] = ""
+        for key, default in (("port", 554), ("max_width", 1280), ("path", "/")):
+            if values.get(key) in (None, ""):
+                values[key] = default
+        return values
+
+    def addressed(self) -> bool:
+        """True when this entry actually names something to connect to.
+
+        The bundled config declares a camera whose address comes from the
+        environment, for development. On an installed PC there is no such
+        environment, so that entry resolves to a camera with no address - and
+        seeding it would put a permanently-failing camera nobody added into
+        every fresh install, retrying a connection to "" forever. An entry with
+        no url, no host and no webcam is not a camera.
+        """
+        return bool(self.url or self.host) or self.webcam is not None
+
     def source(self) -> "str | int":
         """Resolved capture source: webcam index, explicit URL, or a URL
         built from parts with percent-encoded credentials."""
diff --git a/tests/test_config.py b/tests/test_config.py
index 5144995..dee7807 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1,6 +1,8 @@
 """The shipped YAML carries thresholds measured on the deployment site; the
 pydantic defaults must not drift away from them (a trimmed config would then
 silently re-admit the false positives those values were tuned to reject)."""
+from pathlib import Path
+
 import pytest
 
 from behavision.config import (ApiSection, Config, DetectionSection,
@@ -123,3 +125,62 @@ def test_no_usable_model_fails_loudly(tmp_path):
     (tmp_path / "w600k_mbf.onnx").write_bytes(b"garbage")
     with pytest.raises(FileNotFoundError, match="no usable recognition model"):
         ArcFaceEncoder(tmp_path)
+
+
+def _no_env(monkeypatch, tmp_path):
+    """Make the process look like an installed PC rather than a checkout.
+
+    `load_config` calls `load_dotenv` first, so simply unsetting the variables
+    is not enough in a working tree - the .env sitting next to the code puts
+    them straight back. Removing the .env from the picture is the condition
+    these tests are actually about.
+    """
+    import behavision.paths as paths
+    monkeypatch.setattr(paths, "env_file", lambda: None)
+    for var in ("BEHAVISION_CAM1_HOST", "BEHAVISION_CAM1_USERNAME",
+                "BEHAVISION_CAM1_PASSWORD", "BEHAVISION_API_USER",
+                "BEHAVISION_API_PASSWORD", "BEHAVISION_WEBHOOK_URL"):
+        monkeypatch.delenv(var, raising=False)
+    monkeypatch.setenv("BEHAVISION_DATA_DIR", str(tmp_path))
+
+
+def test_the_bundled_config_loads_with_no_environment_at_all(tmp_path, monkeypatch):
+    """What a freshly installed PC looks like: config/default.yaml, and nothing
+    else.
+
+    Every `${VAR}` in that file then resolves to YAML null. The engine's own
+    sections already guarded against that; the camera section did not, so the
+    shipped config raised three pydantic errors on host, username and password
+    and the engine would not start at all on any machine without a developer's
+    .env - which is every machine the product is installed on. It was found by
+    cloning the repository and running this suite, never by working in a
+    checkout where .env is right there.
+    """
+    _no_env(monkeypatch, tmp_path)
+
+    root = Path(__file__).resolve().parent.parent
+    cfg = load_config(root / "config" / "default.yaml")
+
+    assert cfg.api.username == ""
+    assert cfg.api.port == 8010
+    for cam in cfg.cameras:
+        assert cam.host == "" and cam.username == "" and cam.password == ""
+        assert cam.port == 554
+
+
+def test_a_camera_with_no_address_is_not_seeded(tmp_path, monkeypatch):
+    """The bundled config declares a camera whose address comes from the
+    environment. On an installed PC there is none, so seeding it would put a
+    camera the shop never added into a brand new install, permanently failing
+    to connect to "" - and their first task would be working out what it was."""
+    from behavision.cameras import CameraStore
+
+    _no_env(monkeypatch, tmp_path)
+
+    root = Path(__file__).resolve().parent.parent
+    cfg = load_config(root / "config" / "default.yaml")
+
+    store = CameraStore(tmp_path / "cameras.json")
+    assert store.seed(cfg.cameras) is False
+    assert store.list() == []
+    assert not (tmp_path / "cameras.json").exists()