fix: clean up nodeActivity in pruneStaleNodes to prevent memory leak (#553)

## Summary

`nodeActivity` (an object tracking per-node packet counts for heatmap
intensity) grows without bound — entries are added on every packet flash
but never removed, even when stale nodes are pruned.

## Changes

- **Delete `nodeActivity[key]`** alongside `nodeMarkers[key]` and
`nodeData[key]` when removing stale WS-only nodes in `pruneStaleNodes()`
- **Prune orphaned entries** — after the main prune loop, sweep
`nodeActivity` and delete any key that has no corresponding `nodeData`
entry (catches edge cases where nodes were removed by other code paths)
- Both run every 60s via the existing `pruneStaleNodes` interval timer

## Testing

- Added 2 regression tests in `test-frontend-helpers.js` verifying stale
node cleanup and orphan removal
- All 435 frontend helper tests pass, plus packet-filter (62) and aging
(29)

Fixes #390

---------

Co-authored-by: you <you@example.com>

public/live.js

@@ -1650,6 +1650,7 @@
           }
           delete nodeMarkers[key];
           delete nodeData[key];
+          delete nodeActivity[key];
           pruned = true;
         }
       } else if (marker && marker._staleDimmed) {
@@ -1665,12 +1666,17 @@
       if (_el2) _el2.textContent = Object.keys(nodeMarkers).length;
       if (window.HopResolver) HopResolver.init(Object.values(nodeData));
     }
+    // Prune orphaned nodeActivity entries (nodes removed above or never tracked)
+    for (var aKey in nodeActivity) {
+      if (!(aKey in nodeData)) delete nodeActivity[aKey];
+    }
   }
 
   // Expose for testing
   window._livePruneStaleNodes = pruneStaleNodes;
   window._liveNodeMarkers = function() { return nodeMarkers; };
   window._liveNodeData = function() { return nodeData; };
+  window._liveNodeActivity = function() { return nodeActivity; };
   window._vcrFormatTime = vcrFormatTime;
   window._liveDbPacketToLive = dbPacketToLive;
   window._liveExpandToBufferEntries = expandToBufferEntries;

test-frontend-helpers.js

@@ -998,6 +998,56 @@ console.log('\n=== live.js: pruneStaleNodes ===');
     assert.ok(markers['apiNode'], 'API stale node should NOT be removed');
     assert.ok(data['apiNode'], 'API stale node data should NOT be removed');
   });
+
+  test('pruneStaleNodes cleans up nodeActivity for removed nodes', () => {
+    const { ctx } = makeLiveSandbox();
+    const prune = ctx.window._livePruneStaleNodes;
+    const markers = ctx.window._liveNodeMarkers();
+    const data = ctx.window._liveNodeData();
+    const activity = ctx.window._liveNodeActivity();
+
+    // WS-only stale node
+    markers['staleNode'] = { _glowMarker: null };
+    data['staleNode'] = { public_key: 'staleNode', role: 'companion', _liveSeen: Date.now() - 48 * 3600000 };
+    activity['staleNode'] = 5;
+
+    // Active node
+    markers['activeNode'] = { setStyle: function() {}, _glowMarker: null };
+    data['activeNode'] = { public_key: 'activeNode', role: 'companion', _liveSeen: Date.now() };
+    activity['activeNode'] = 3;
+
+    prune();
+
+    assert.ok(!markers['staleNode'], 'stale node marker removed');
+    assert.ok(!data['staleNode'], 'stale node data removed');
+    assert.ok(!activity['staleNode'], 'stale node activity removed');
+    assert.ok(markers['activeNode'], 'active node marker preserved');
+    assert.ok(data['activeNode'], 'active node data preserved');
+    assert.strictEqual(activity['activeNode'], 3, 'active node activity preserved');
+  });
+
+  test('pruneStaleNodes removes orphaned nodeActivity entries', () => {
+    const { ctx } = makeLiveSandbox();
+    const prune = ctx.window._livePruneStaleNodes;
+    const markers = ctx.window._liveNodeMarkers();
+    const data = ctx.window._liveNodeData();
+    const activity = ctx.window._liveNodeActivity();
+
+    // Add an active node
+    markers['existingNode'] = { setStyle: function() {}, _glowMarker: null };
+    data['existingNode'] = { public_key: 'existingNode', role: 'companion', _liveSeen: Date.now() };
+    activity['existingNode'] = 2;
+
+    // Add orphaned activity (no corresponding nodeData)
+    activity['ghostNode'] = 10;
+
+    prune();
+
+    assert.ok(markers['existingNode'], 'existing node preserved');
+    assert.ok(data['existingNode'], 'existing node data preserved');
+    assert.strictEqual(activity['existingNode'], 2, 'existing node activity preserved');
+    assert.ok(!activity['ghostNode'], 'orphaned activity entry removed');
+  });
 }
 
 // ===== live.js: vcrFormatTime respects UTC/local setting =====