fix: distinguish partial vessel snapshots from stale data

src/ui/layerPanel.test.mjs

@@ -29,3 +29,63 @@ test('panel presentation places Transit between Street Traffic and Bike Share in
   );
   assert.equal(order.filter(({ id }) => id === 'transit').length, 1);
 });
+
+test('partial feed controls distinguish incomplete records from stale data and outages', async () => {
+  const { LayerPanel, layerFeedState } = await import('./layerPanel.js');
+  const classes = new Map();
+  const attrs = new Map();
+  const button = {
+    classList: { toggle: (key, value) => classes.set(key, value) },
+    dataset: {},
+    setAttribute: (key, value) => attrs.set(key, value),
+  };
+  const layer = {
+    id: 'ais-live-vessels',
+    name: 'Live Vessels',
+    source: 'AISStream',
+    enabled: true,
+    stats: {
+      partial: true,
+      stale: false,
+      count: 2,
+      acceptedRowCount: 2,
+      rawRowCount: 3,
+      lastUpdate: Date.now(),
+    },
+  };
+  const panel = LayerPanel.prototype;
+  panel._syncToggleButton(button, layer);
+  assert.equal(button.textContent, 'PARTIAL');
+  assert.equal(button.dataset.feedState, 'partial');
+  assert.equal(classes.get('feed-partial'), true);
+  assert.equal(classes.get('feed-stale'), false);
+  assert.match(attrs.get('aria-label'), /PARTIAL/);
+  assert.match(
+    panel._buildMetaText(layer),
+    /^PARTIAL · AISStream · 2 of 3 records accepted · /,
+  );
+  assert.match(
+    panel._buildMetaText({
+      ...layer,
+      stats: { ...layer.stats, rawRowCount: 2 },
+    }),
+    /incomplete snapshot/,
+  );
+  assert.equal(layerFeedState({ ...layer.stats, stale: true }), 'stale');
+  assert.equal(
+    layerFeedState({ ...layer.stats, error: 'Connection lost' }),
+    'degraded',
+  );
+  assert.equal(
+    layerFeedState({ ...layer.stats, status: 'unavailable' }),
+    'unavailable',
+  );
+  assert.equal(layerFeedState({ ...layer.stats, loading: true }), 'loading');
+  layer.stats = { ...layer.stats, partial: false };
+  panel._syncToggleButton(button, layer);
+  assert.equal(button.textContent, 'ON');
+  assert.equal(classes.get('feed-partial'), false);
+  layer.enabled = false;
+  panel._syncToggleButton(button, layer);
+  assert.equal(button.textContent, 'OFF');
+});