diff --git a/src/layers/alpr/edgeCases.test.mjs b/src/layers/alpr/edgeCases.test.mjs
new file mode 100644
index 000000000..120d03ce6
--- /dev/null
+++ b/src/layers/alpr/edgeCases.test.mjs
@@ -0,0 +1,131 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { PbfWriter } from 'pbf';
+import * as geo from '../../geo/index.js';
+import { tilesForBounds, tileToBBox } from '../../data/tomtomTiles.js';
+import { alprDetailZoom, createAlprTileSource } from './source.js';
+import { validateAlprSnapshot } from './model.js';
+import { directionWedgePositions } from './visuals.js';
+import { decodeAlprTile } from './tileRecords.js';
+import { DIRECTION_CONE_HALF_ANGLE_DEG } from './policy.js';
+
+const EXTENT = 4096;
+const box = { south: 30.25, north: 30.3, west: -97.8, east: -97.7 };
+
+/** Encode one `cameras` layer holding point features (MVT 2.1). */
+function encodeCameraTile(points) {
+  const keys = [];
+  const values = [];
+  const index = (list, value) => {
+    const at = list.indexOf(value);
+    return at === -1 ? list.push(value) - 1 : at;
+  };
+  const zigzag = (n) => (n << 1) ^ (n >> 31);
+  const features = points.map(({ x, y, properties }) => {
+    const tags = [];
+    for (const [key, value] of Object.entries(properties))
+      tags.push(index(keys, key), index(values, String(value)));
+    return { tags, geometry: [9, zigzag(x), zigzag(y)] };
+  });
+  const pbf = new PbfWriter();
+  pbf.writeMessage(3, (_layer, out) => {
+    out.writeVarintField(15, 2);
+    out.writeStringField(1, 'cameras');
+    for (const feature of features)
+      out.writeMessage(2, (_f, w) => {
+        w.writePackedVarint(2, feature.tags);
+        w.writeVarintField(3, 1);
+        w.writePackedVarint(4, feature.geometry);
+      });
+    for (const key of keys) out.writeStringField(3, key);
+    for (const value of values)
+      out.writeMessage(4, (_v, w) => w.writeStringField(1, value));
+    out.writeVarintField(5, EXTENT);
+  });
+  return pbf.finish();
+}
+
+const metadata = (country) => ({
+  tiles: [
+    `https://tiles.dontgetflocked.com/cameras-${country}-hourly/{z}/{x}/{y}.mvt`,
+  ],
+  bounds: country === 'ca' ? [-124, 42, -63, 54] : [-160, 17, -64, 59],
+});
+
+/** Initial great-circle bearing from one Cartesian to another, in degrees. */
+function bearingDeg(from, to) {
+  const a = geo.cartographic.fromCartesian(from);
+  const b = geo.cartographic.fromCartesian(to);
+  const dLon = b.longitude - a.longitude;
+  const y = Math.sin(dLon) * Math.cos(b.latitude);
+  const x =
+    Math.cos(a.latitude) * Math.sin(b.latitude) -
+    Math.sin(a.latitude) * Math.cos(b.latitude) * Math.cos(dLon);
+  return ((Math.atan2(y, x) * 180) / Math.PI + 360) % 360;
+}
+
+test('edge:alpr-cameras: a camera on a tile edge is one record with its own azimuth', async () => {
+  const zoom = alprDetailZoom(box);
+  const tiles = tilesForBounds(box, zoom, { maxTiles: 17 });
+  // Two horizontally adjacent tiles of one row share the camera's meridian.
+  const west = tiles.find((tile) =>
+    tiles.some((other) => other.x === tile.x + 1 && other.y === tile.y),
+  );
+  const east = { x: west.x + 1, y: west.y };
+  const edgeLon = tileToBBox(zoom, west.x, west.y).east;
+  assert.equal(edgeLon, tileToBBox(zoom, east.x, east.y).west);
+  const camera = {
+    osmType: 'node',
+    osmId: 424242,
+    direction: 135,
+    brand: 'Fixture',
+  };
+  const bytes = new Map([
+    [
+      `${west.x}/${west.y}`,
+      encodeCameraTile([{ x: EXTENT, y: 2048, properties: camera }]),
+    ],
+    [
+      `${east.x}/${east.y}`,
+      encodeCameraTile([{ x: 0, y: 2048, properties: camera }]),
+    ],
+  ]);
+  // Both tiles really carry the camera, at the same longitude.
+  const decoded = [west, east].map(
+    ({ x, y }) => decodeAlprTile(bytes.get(`${x}/${y}`), zoom, x, y)[0],
+  );
+  assert.deepEqual(
+    decoded.map((r) => r.id),
+    ['alpr:424242', 'alpr:424242'],
+  );
+  assert.equal(decoded[0].longitude, decoded[1].longitude);
+  const source = createAlprTileSource({
+    tileFetchImpl: async (url) => {
+      if (url.endsWith('.json'))
+        return Response.json(metadata(url.includes('-ca-') ? 'ca' : 'us'));
+      const [, x, y] = url.match(/\/\d+\/(\d+)\/(\d+)\.mvt$/);
+      return new Response(bytes.get(`${x}/${y}`) ?? encodeCameraTile([]));
+    },
+  });
+  const snapshot = validateAlprSnapshot(await source.fetch(box));
+  const matches = snapshot.records.filter((r) => r.id === 'alpr:424242');
+  assert.equal(matches.length, 1);
+  assert.equal(snapshot.records.length, 1);
+  const [record] = matches;
+  assert.ok(Math.abs(record.longitude - edgeLon) < 1e-9);
+  assert.equal(record.directionDeg, 135);
+
+  // The bearing wedge is centred on the tagged azimuth.
+  const [apex, left, right] = directionWedgePositions(record);
+  const leftDeg = bearingDeg(apex, left);
+  const rightDeg = bearingDeg(apex, right);
+  assert.ok(Math.abs(leftDeg - (135 - DIRECTION_CONE_HALF_ANGLE_DEG)) < 0.01);
+  assert.ok(Math.abs(rightDeg - (135 + DIRECTION_CONE_HALF_ANGLE_DEG)) < 0.01);
+
+  // A repeat read (the other engine's scene) keeps the same identity.
+  const again = await source.fetch(box);
+  assert.deepEqual(
+    again.records.map((r) => [r.id, r.latitude, r.longitude, r.directionDeg]),
+    [[record.id, record.latitude, record.longitude, record.directionDeg]],
+  );
+});