fix: auto scroll not working for the final assistant message

[AdityaHegde]

In chat history we autoscroll to the bottom if the user was already at the bottom. We do this by checking if a new block has come in. But if the block type changes then the scroll height could change, especially when a long large assistant message block replaces the "working" block.

Adding an additional check for block type change to fix this.

This simulates a conversation by modifying query cache of an existing conversaiont. Call this on mount somewhere. Running on a rill developer file edit chat will give the best results.

import type { Conversation } from "@rilldata/web-common/features/chat/core/conversation.ts";
import { asyncWait, waitUntil } from "@rilldata/web-common/lib/waitUtils.ts";
import { get } from "svelte/store";
import {
  getRuntimeServiceGetConversationQueryKey,
  type V1Message,
} from "@rilldata/web-common/runtime-client";
import { runtime } from "@rilldata/web-common/runtime-client/runtime-store.ts";
import { queryClient } from "@rilldata/web-common/lib/svelte-query/globalQueryClient.ts";

export async function simulateConversation(
  conversation: Conversation,
  beforeStart: () => void,
) {
  const convQuery = conversation.getConversationQuery();
  await waitUntil(() => !get(convQuery).isPending);

  const resp = get(convQuery).data;
  if (!resp || !resp.messages) return;

  const queryKey = getRuntimeServiceGetConversationQueryKey(
    get(runtime).instanceId,
    conversation.conversationId,
  );
  const messages: V1Message[] = [];
  const updateQueryCache = (message: V1Message) => {
    messages.push({
      ...message,
      createdOn: new Date().toISOString(),
      updatedOn: new Date().toISOString(),
    });
    queryClient.setQueryData(queryKey, {
      conversation: resp.conversation,
      messages,
    });
  };

  beforeStart();
  conversation.isStreaming.set(true);

  updateQueryCache(resp.messages[0]);
  for (let i = 1; i < resp.messages.length; i++) {
    const prev = new Date(resp.messages[i - 1].createdOn!);
    const now = new Date(resp.messages[i].updatedOn!);
    // Dividing by 5 to speed things up.
    await asyncWait((now.getTime() - prev.getTime()) / 5);

    updateQueryCache(resp.messages[i]);
  }

  await asyncWait(500); 
  conversation.isStreaming.set(false);
}

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!