Limit mobile event history to prevent freezes

[RobertEmprechtinger]

Fixes a browser freeze observed with codewhale serve --mobile on long code-generation threads. The mobile page now keeps only the latest 100 visible events in the DOM, and the thread events SSE endpoint accepts replay_limit so the mobile page does not replay an entire old thread into the browser. Tested locally with serve --mobile on a long generation thread; the mobile browser stayed responsive after the change.

[greptile-apps]

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[github-actions]

Thanks @RobertEmprechtinger for taking the time to contribute.

This repository is observing a maintainer-managed PR intake gate in dry-run mode, so this pull request is staying open. This note helps maintainers prepare the allowlist before any enforcement is considered.

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[gemini-code-assist]

Code Review

This pull request introduces a replay_limit parameter to the thread events API and updates the mobile TUI client to limit the number of visible events to 100, pruning older events from the DOM to improve performance. The reviewer feedback is highly constructive and suggests: 1) restricting the server-side replay_limit pruning to initial requests (where since_seq is 0 or unset) to avoid gaps in active streams, and 2) implementing sequence number tracking (lastSeq) in the client to filter out duplicate events that may be replayed during automatic EventSource reconnections.

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[gemini-code-assist]

Applying replay_limit when since_seq is greater than 0 can cause the client to miss events between since_seq and the start of the pruned backlog, leading to state inconsistency or gaps in the event stream. It is safer to only apply the limit when starting a new stream (i.e., since_seq is None or 0).

Suggested change

	if let Some(limit) = query.replay_limit
	&& backlog.len() > limit
	{
	backlog = backlog.split_off(backlog.len() - limit);
	}
	if let Some(limit) = query.replay_limit
	&& query.since_seq.unwrap_or(0) == 0
	&& backlog.len() > limit
	{
	backlog = backlog.split_off(backlog.len() - limit);
	}

[gemini-code-assist]

Initialize lastSeq in the state object to track the sequence number of the last processed event. This will be used to prevent duplicate events from being appended to the DOM if the EventSource automatically reconnects.

Suggested change

	const state = {
	threadId: "",
	activeTurnId: "",
	const state = {
	threadId: "",
	activeTurnId: "",
	lastSeq: 0,

[gemini-code-assist]

Reset state.lastSeq to 0 when selecting a new thread to ensure we correctly accept the replayed backlog events for the new thread.

Suggested change

	$("events").innerHTML = "";
	if (state.source) state.source.close();
	const qs = "?since_seq=0" + (token() ? "&token=" + encodeURIComponent(token()) : "");
	const qs = "?since_seq=0&replay_limit=" + MAX_VISIBLE_EVENTS +
	(token() ? "&token=" + encodeURIComponent(token()) : "");
	$("events").innerHTML = "";
	state.lastSeq = 0;
	if (state.source) state.source.close();
	const qs = "?since_seq=0&replay_limit=" + MAX_VISIBLE_EVENTS +
	(token() ? "&token=" + encodeURIComponent(token()) : "");

[gemini-code-assist]

Add a check to ignore duplicate events based on their sequence number (seq). Since EventSource automatically reconnects with since_seq=0 on network hiccups, the server will replay the backlog, which would otherwise result in duplicate events being appended to the chat history.

Suggested change

	$("events").appendChild(item);
	pruneVisibleEvents();
	state.eventCount += 1;
	$("event-count").textContent = state.eventCount + " events";
	const visible = Math.min(state.eventCount, MAX_VISIBLE_EVENTS);
	$("event-count").textContent = visible + " of " + state.eventCount + " events";
	if (data && data.seq) {
	if (data.seq <= state.lastSeq) return;
	state.lastSeq = data.seq;
	}
	$("events").appendChild(item);
	pruneVisibleEvents();
	state.eventCount += 1;
	const visible = Math.min(state.eventCount, MAX_VISIBLE_EVENTS);
	$("event-count").textContent = visible + " of " + state.eventCount + " events";