diff --git a/.github/workflows/wheels.yml b/.github/workflows/wheels.yml
index 5434c7f9..7522745c 100644
--- a/.github/workflows/wheels.yml
+++ b/.github/workflows/wheels.yml
@@ -24,11 +24,14 @@ jobs:
           CIBW_ARCHS_WINDOWS: AMD64
           CIBW_MANYLINUX_X86_64_IMAGE: manylinux_2_28
           CIBW_BUILD_VERBOSITY: "1"
-          CIBW_TEST_REQUIRES: "numpy pyyaml"
+          # matplotlib/pillow are the [plot] extra; vdsim_render imports them at
+          # module scope, so the import closure check below needs them present.
+          CIBW_TEST_REQUIRES: "numpy pyyaml matplotlib pillow"
           CIBW_TEST_COMMAND: >-
             python -c "import vdsim; print(vdsim.__file__)" &&
             python -c "from vdsim_lab import Sim; Sim(vehicle='sedan', level='L2'); print('sedan ok')" &&
-            python -c "from vdsim_lab import Sim; Sim(vehicle='ioniq5_awd', tire='ioniq5_pac2002', level='L2'); print('ioniq5 ok')"
+            python -c "from vdsim_lab import Sim; Sim(vehicle='ioniq5_awd', tire='ioniq5_pac2002', level='L2'); print('ioniq5 ok')" &&
+            python "{project}/tools/wheel_import_smoke.py"
       - uses: actions/upload-artifact@v4
         with:
           name: wheels-${{ matrix.os }}
diff --git a/tools/wheel_import_smoke.py b/tools/wheel_import_smoke.py
new file mode 100755
index 00000000..744f9bba
--- /dev/null
+++ b/tools/wheel_import_smoke.py
@@ -0,0 +1,123 @@
+#!/usr/bin/env python3
+"""Import every first-party module the wheel claims to ship, from the wheel.
+
+Run by ``CIBW_TEST_COMMAND`` inside cibuildwheel's test environment, where the
+wheel is installed and the source tree is present but not on ``sys.path``.
+
+Why this exists
+---------------
+Measured 2026-09-18 (pre-flight C-2): the wheel shipped ``vdsim_render.py`` but
+not ``vdsim_preset.py``, which it imports, so ``import vdsim_render`` raised
+``ModuleNotFoundError`` for every pip user. The whole wheel matrix was green:
+the old test command imported ``vdsim`` and built ``Sim`` twice, and
+``tools/verify_wheel_packaging.py`` compares zip members against a hand-written
+list that never named either module.
+
+The module list is read from ``python/CMakeLists.txt`` — the file that decides
+what ships — so the workflow never restates names that can drift.
+
+Two properties are checked per module:
+
+1. it imports at all;
+2. it resolves to the installed distribution, not to the source tree. Without
+   (2) this check would pass on a broken wheel whenever the working directory
+   happened to be the repository.
+"""
+from __future__ import annotations
+
+import importlib
+import re
+import sys
+from pathlib import Path
+
+REPO = Path(__file__).resolve().parents[1]
+MANIFEST = REPO / "python" / "CMakeLists.txt"
+
+
+def shipped_modules():
+    """Top-level importable names listed under ``if(DEFINED SKBUILD)``.
+
+    ``install(FILES ...)`` entries ending in ``.py`` become module names;
+    ``install(DIRECTORY .../python/<name> ...)`` entries become package names.
+    Config directories (``configs/...``) are data, not importable, and are
+    skipped.
+    """
+    text = MANIFEST.read_text()
+    if "if(DEFINED SKBUILD)" not in text:
+        raise SystemExit("FAIL: no SKBUILD install block in %s" % MANIFEST)
+    body = text.split("if(DEFINED SKBUILD)", 1)[1].split("endif()", 1)[0]
+    names = ["vdsim"]  # install(TARGETS vdsim_py ...) -> the extension module
+    for rel in re.findall(r"\$\{CMAKE_SOURCE_DIR\}/([^\s)]+)", body):
+        parts = rel.split("/")
+        if rel.endswith(".py"):
+            names.append(parts[-1][:-3])
+        elif parts[0] == "python":
+            names.append(parts[-1])
+    out = []
+    for n in names:  # stable order, no duplicates
+        if n not in out:
+            out.append(n)
+    return out
+
+
+def strip_source_tree_from_path():
+    """Drop anything that could satisfy an import from the checkout.
+
+    Returns the removed entries so the report can show what was excluded.
+    """
+    removed = []
+    kept = []
+    for entry in sys.path:
+        try:
+            resolved = Path(entry or ".").resolve()
+        except OSError:
+            kept.append(entry)
+            continue
+        if resolved == REPO or REPO in resolved.parents:
+            removed.append(str(resolved))
+        else:
+            kept.append(entry)
+    sys.path[:] = kept
+    return removed
+
+
+def main():
+    removed = strip_source_tree_from_path()
+    modules = shipped_modules()
+    print("manifest: %s" % MANIFEST)
+    print("removed from sys.path (source tree): %s" % (removed or "none"))
+    print("modules to import (%d): %s" % (len(modules), ", ".join(modules)))
+
+    failures = []
+    for name in modules:
+        try:
+            mod = importlib.import_module(name)
+        except Exception as exc:                       # noqa: BLE001 - report any
+            failures.append("%s: %s: %s" % (name, type(exc).__name__, exc))
+            print("FAIL %-16s %s: %s" % (name, type(exc).__name__, exc))
+            continue
+        origin = getattr(mod, "__file__", None)
+        if origin is None:
+            failures.append("%s: imported with no __file__" % name)
+            print("FAIL %-16s no __file__" % name)
+            continue
+        origin_path = Path(origin).resolve()
+        if origin_path == REPO or REPO in origin_path.parents:
+            failures.append("%s: resolved to the source tree (%s)" % (name, origin_path))
+            print("FAIL %-16s from source tree %s" % (name, origin_path))
+            continue
+        print("ok   %-16s %s" % (name, origin_path))
+
+    if failures:
+        print("\n%d module(s) failed:" % len(failures))
+        for f in failures:
+            print("  - %s" % f)
+        print("The wheel does not ship a working copy of every module listed in "
+              "python/CMakeLists.txt. Add the missing file to that install list.")
+        return 1
+    print("\nall %d shipped modules import from the installed wheel" % len(modules))
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())