fix: prevent favicon data retention in heartbeat debug logs

[TimeToBuildBob]

Problem

The heartbeat module passes entire Tab objects to console.debug(). In Firefox, Tab.favIconUrl is a base64 data URI (often 10-20 KB). Browser console buffers retain references to logged objects, so over thousands of heartbeats the retained Tab references accumulate hundreds of MBs of duplicate favicon data in memory.

From the about:memory report in #222:

• ~761 MB of strings — all base64-encoded favicon/icon data
• One favicon: 8,804 copies × ~22 KB each = 189 MB
• Another: 17,426 copies × ~9 KB each = 157 MB

Fix

1. Destructure tab early: Extract only url, title, audible, incognito from the Tab object, so the full object (including favIconUrl) can be GC'd immediately
2. Log only URL strings: Replace console.debug('...', tab) with console.debug('...', tab.url) — retains useful debug info without retaining the full object

This is the favicon half of #222. The AbortController leak (the other half, ~123 MB of leaked controllers + ~645 MB of closures) is being addressed in aw-client-js via ActivityWatch/aw-client-js#50.

Test plan

• Build passes (npm run build)
• Extension loads in Firefox/Chrome and sends heartbeats normally
• After extended use, about:memory no longer shows large favicon string accumulation under the extension's background page

[greptile-apps]

Greptile Summary

This PR fixes a significant memory leak in Firefox where console.debug calls were retaining references to full Tab objects (including favIconUrl, a base64 data URI of 10–20 KB) in the browser's console buffer across thousands of heartbeats. The fix correctly replaces console.debug('...', tab) with console.debug('...', tab.url) in all listener functions, ensuring the console buffer only retains small strings.

Confidence Score: 5/5

Safe to merge — the core memory leak fix is correct and complete; only a minor over-removal of small safe data from two internal debug logs.

All findings are P2. The listener-level debug log changes correctly eliminate Tab object retention in the console buffer. The only concern is that previousData and data (neither of which contain favicon content) were also removed from two internal log calls, reducing debuggability without fixing any memory issue — but this does not affect runtime correctness or the leak fix itself.

No files require special attention beyond the single P2 suggestion on heartbeat.ts.

Important Files Changed

Filename	Overview
src/background/heartbeat.ts	Correctly eliminates Tab object references from console.debug calls to prevent console-buffer memory retention of large favIconUrl base64 strings; two debug log statements inside heartbeat() also remove small, safe data objects unnecessarily.

Sequence Diagram

sequenceDiagram
    participant Listener as Listener (alarm/tab/init)
    participant HB as heartbeat()
    participant Console as console.debug buffer
    participant GC as Garbage Collector

    Note over Listener,GC: BEFORE fix
    Listener->>Console: console.debug('...', tab) — retains Tab + favIconUrl
    Listener->>HB: heartbeat(client, tab, tabCount)
    HB->>Console: console.debug('Sending heartbeat', data)
    Note over Console: Tab object pinned in buffer<br/>favIconUrl (~20 KB) × thousands = ~761 MB leak

    Note over Listener,GC: AFTER fix
    Listener->>Console: console.debug('...', tab.url) — retains only string
    Listener->>HB: heartbeat(client, tab, tabCount)
    HB-->>GC: Tab object eligible for GC after function returns
    HB->>Console: console.debug('Sending heartbeat', url)
    Note over Console: Only URL strings retained — no favicon data

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_{Reviews (1): Last reviewed commit: "fix: prevent favicon data retention in h..." | Re-trigger Greptile}

[greptile-apps]

Over-removal of debug context for small data objects

previousData and data are both plain IEvent['data'] objects containing only url, title, audible, incognito, and tabCount — no favIconUrl or other large base64 content. Removing them from these two log calls reduces debugging utility (e.g., you can no longer see what changed between heartbeats, or what audible/incognito state was sent) without addressing any memory issue. The leak came from logging the full Tab object in the listener functions, not from logging data or previousData.

Suggested change

	console.debug('Sending heartbeat for previous data', previousData)

And on line 54:

Suggested change

	console.debug('Sending heartbeat', data)

[TimeToBuildBob]

Good catch. and only contain small fields (url, title, audible, incognito, tabCount) — no favicon data. Restoring them is the right call for debuggability. Fixed in bb10813.

[ErikBjare]

@TimeToBuildBob Valid concern in #223 (comment)