m: In patchRemoveAllListeners we are removing the event from the map. In this function we keep the map as is, is this difference intended?

Added comments to explain this, here is the AI summary of why this is expected:

es, that difference is intentional and load-bearing — it's not an oversight.

The map is Map<event, WeakMap<userListener, boundWrapper>> (outer keyed by event-name string, inner keyed weakly by the user's listener).

Why patchRemoveListener must keep the entry: the whole design reuses one stable wrapper per listener (patchAddListener, lines 125–131), and Node's EventEmitter allows and counts
duplicate registrations. So a single user listener can be registered multiple times, all sharing the same wrapper B:

ee.on('data', fn); // registers wrapper B (map[data][fn] = B)
ee.on('data', fn); // registers B again — Node now has 2 copies of B
ee.removeListener('data', fn); // removes ONE copy of B

If removeListener deleted map[data][fn] here, the second still-registered copy of B would become orphaned: the next removeListener('data', fn) would no longer find B in the map, fall
through to original.apply(this, args) with the raw fn (line 149–150), and fail to match/remove the wrapper. So the mapping has to survive a single removal because other registrations of
the same wrapper may still be live.

Why patchRemoveAllListeners can delete it: removeAllListeners(event) tears down every listener for that event in one shot, so no registration referencing those wrappers remains. The map
entry is then unambiguously stale, and deleting it is safe — and a genuine cleanup, because the outer map is a plain Map keyed by event-name strings, which would otherwise accumulate
those keys forever. (The no-arg case resets the whole map, lines 162–164.)

Why leaving stale inner entries after removeListener isn't a leak: the inner structure is a WeakMap keyed by the user's listener, so once the user drops their reference to fn, the entry
is GC'd on its own. There's nothing to manually clean up there, and reusing the same wrapper if fn is re-added later is actually desirable (it preserves DOM EventTarget's (type,
callback, capture) dedup, per the comment on lines 6–14).

So: keep-on-single-remove (correctness, due to possible duplicates) vs. delete-on-remove-all (safe cleanup of the strong outer map) is the right asymmetry.

l: Any reason why not a Map is used? Then we wouldn't need to use type assertions

good point, this is nicer!