diff --git a/tests/test_dash_layout.py b/tests/test_dash_layout.py
new file mode 100644
index 0000000..a77eb84
--- /dev/null
+++ b/tests/test_dash_layout.py
@@ -0,0 +1,120 @@
+"""The dashboard layout (static/dash-layout.js) holds still (#5713): where a
+widget sits depends on the saved layout and the column count, never on how
+tall each widget's content turned out. Content arrives widget by widget and
+changes on every poll, so a placement that followed the heights moved widgets
+between columns as the page loaded.
+
+These run the real dash-layout.js under node, which CI's job container has
+(its checkout action runs on it). Without node the test skips locally and
+fails in CI, so it can't pass by not running."""
+from __future__ import annotations
+
+import json
+import os
+import random
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+LAYOUT_JS = Path(__file__).resolve().parents[1] / "steward" / "static" / "dash-layout.js"
+NODE = shutil.which("node")
+
+RUNNER = """
+const fs = require("fs");
+global.window = {};
+eval(fs.readFileSync(process.argv[1], "utf8"));
+const L = window.StewardDashLayout;
+const cases = JSON.parse(fs.readFileSync(0, "utf8"));
+process.stdout.write(JSON.stringify(cases.map(c => L.pack(c.items, c.cols))));
+"""
+
+
+def _pack(cases: list[dict]) -> list[dict]:
+    if not NODE:
+        if os.environ.get("CI"):
+            pytest.fail("node is missing from the CI image; the layout test needs it")
+        pytest.skip("needs node")
+    out = subprocess.run([NODE, "-e", RUNNER, str(LAYOUT_JS)], input=json.dumps(cases),
+                         capture_output=True, text=True, timeout=60, check=True)
+    return json.loads(out.stdout)
+
+
+# A saved 12-column layout of the kind the dashboard holds, in saved rows.
+SAVED = [
+    {"id": "overview", "x": 0, "y": 0, "w": 6, "h": 4},
+    {"id": "alerts", "x": 6, "y": 0, "w": 6, "h": 3},
+    {"id": "hosts", "x": 6, "y": 3, "w": 6, "h": 5},
+    {"id": "monitors", "x": 0, "y": 4, "w": 4, "h": 4},
+    {"id": "docker", "x": 4, "y": 4, "w": 2, "h": 6},
+    {"id": "routers", "x": 0, "y": 8, "w": 4, "h": 5},
+    {"id": "chart", "x": 6, "y": 8, "w": 6, "h": 4},
+    {"id": "snmp", "x": 4, "y": 10, "w": 2, "h": 3},
+    {"id": "unifi", "x": 0, "y": 13, "w": 12, "h": 3},
+]
+SPLIT = 7          # view rows per saved row (ROW_SPLIT)
+
+
+def _viewed(fits: dict[str, int] | None = None) -> list[dict]:
+    items = []
+    for s in SAVED:
+        full = s["h"] * SPLIT
+        items.append({"id": s["id"], "x": s["x"], "y": s["y"] * SPLIT, "w": s["w"],
+                      "h": (fits or {}).get(s["id"], full), "full": full})
+    return items
+
+
+def _random_fits(rng: random.Random) -> dict[str, int]:
+    """Content heights as they might land mid-load: some widgets still at
+    their saved height (not measured yet), the rest anywhere from one saved
+    row up to the saved height."""
+    return {s["id"]: rng.randint(SPLIT, s["h"] * SPLIT) for s in SAVED if rng.random() < 0.8}
+
+
+def _overlap(a: dict, b: dict) -> bool:
+    return a["x"] < b["x"] + b["w"] and b["x"] < a["x"] + a["w"]
+
+
+def _shape(pos: dict) -> tuple:
+    """What a reader would notice moving: each widget's column, and which of
+    two widgets sharing a column is above the other."""
+    cols = tuple(sorted((k, p["x"], p["w"]) for k, p in pos.items()))
+    above = tuple(sorted((a, b) for a in pos for b in pos
+                         if a != b and _overlap(pos[a], pos[b]) and pos[a]["y"] < pos[b]["y"]))
+    return cols, above
+
+
+@pytest.mark.parametrize("cols", [12, 16, 18, 24])
+def test_no_content_height_moves_a_widget_to_another_column_or_past_another(cols):
+    rng = random.Random(5713 + cols)
+    cases = [{"items": _viewed(), "cols": cols}] + [
+        {"items": _viewed(_random_fits(rng)), "cols": cols} for _ in range(60)]
+    results = _pack(cases)
+    first = _shape(results[0])
+    for case, pos in zip(cases[1:], results[1:]):
+        assert _shape(pos) == first, {i["id"]: i["h"] for i in case["items"]}
+
+
+@pytest.mark.parametrize("cols", [1, 12, 18, 24])
+def test_each_widget_is_its_fitted_height_with_no_overlap_and_no_gap_above(cols):
+    rng = random.Random(cols)
+    items = _viewed(_random_fits(rng))
+    pos = _pack([{"items": items, "cols": cols}])[0]
+    fit = {i["id"]: i["h"] for i in items}
+    assert {k: p["h"] for k, p in pos.items()} == fit
+    ids = list(pos)
+    for i, a in enumerate(ids):
+        pa = pos[a]
+        assert 0 <= pa["x"] and pa["x"] + pa["w"] <= cols
+        for b in ids[i + 1:]:
+            pb = pos[b]
+            assert not (_overlap(pa, pb) and pa["y"] < pb["y"] + pb["h"] and pb["y"] < pa["y"] + pa["h"]), (a, b)
+        # Nothing could rise: it sits on the top or on a widget in its columns.
+        assert pa["y"] == 0 or any(_overlap(pa, pos[o]) and pos[o]["y"] + pos[o]["h"] == pa["y"]
+                                   for o in ids if o != a), a
+
+
+def test_twelve_columns_keep_the_saved_columns():
+    pos = _pack([{"items": _viewed(), "cols": 12}])[0]
+    assert {k: (p["x"], p["w"]) for k, p in pos.items()} == {s["id"]: (s["x"], s["w"]) for s in SAVED}