fix: prevent favicon data retention in heartbeat debug logs

The console.debug calls passed entire Tab objects, which in Firefox
include favIconUrl as base64 data URIs. Browser console buffers retain
references to logged objects, so over thousands of heartbeats this
accumulated hundreds of MBs of duplicate favicon data in memory.

Fix: destructure only needed fields from Tab objects before use, and
log only the URL string instead of the full Tab object.

This addresses the favicon accumulation half of ActivityWatch#222 (the
AbortController leak is being fixed in aw-client-js via
ActivityWatch/aw-client-js#50).

Author: TimeToBuildBob

src/background/heartbeat.ts

@@ -27,17 +27,22 @@ async function heartbeat(
     return
   }
 
+  // Extract only the fields we need so we don't retain references to the
+  // full Tab object (which includes favIconUrl — a potentially large base64
+  // data URI).  Over thousands of heartbeats the retained Tab references
+  // cause unbounded memory growth (see #222).
+  const { url, title, audible, incognito } = tab
   const now = new Date()
   const data: IEvent['data'] = {
-    url: tab.url,
-    title: tab.title,
-    audible: tab.audible ?? false,
-    incognito: tab.incognito,
+    url,
+    title,
+    audible: audible ?? false,
+    incognito,
     tabCount: tabCount,
   }
   const previousData = await getHeartbeatData()
   if (previousData && !deepEqual(previousData, data)) {
-    console.debug('Sending heartbeat for previous data', previousData)
+    console.debug('Sending heartbeat for previous data')
     await sendHeartbeat(
       client,
       await getBucketId(),
@@ -46,7 +51,7 @@ async function heartbeat(
       config.heartbeat.intervalInSeconds + 20,
     )
   }
-  console.debug('Sending heartbeat', data)
+  console.debug('Sending heartbeat', url)
   await sendHeartbeat(
     client,
     await getBucketId(),
@@ -60,7 +65,7 @@ async function heartbeat(
 export const sendInitialHeartbeat = async (client: AWClient) => {
   const activeWindowTab = await getActiveWindowTab()
   const tabs = await getTabs()
-  console.debug('Sending initial heartbeat', activeWindowTab)
+  console.debug('Sending initial heartbeat', activeWindowTab?.url)
   await heartbeat(client, activeWindowTab, tabs.length)
 }
 
@@ -70,7 +75,7 @@ export const heartbeatAlarmListener =
     const activeWindowTab = await getActiveWindowTab()
     if (!activeWindowTab) return
     const tabs = await getTabs()
-    console.debug('Sending heartbeat for alarm', activeWindowTab)
+    console.debug('Sending heartbeat for alarm', activeWindowTab.url)
     await heartbeat(client, activeWindowTab, tabs.length)
   }
 
@@ -79,6 +84,6 @@ export const tabActivatedListener =
   async (activeInfo: browser.Tabs.OnActivatedActiveInfoType) => {
     const tab = await getTab(activeInfo.tabId)
     const tabs = await getTabs()
-    console.debug('Sending heartbeat for tab activation', tab)
+    console.debug('Sending heartbeat for tab activation', tab.url)
     await heartbeat(client, tab, tabs.length)
   }