v3: AI SDK pivot — pi removed, Next.js 16 + AI SDK 7 + AI Elements teacher app

The teaching agent no longer runs on pi. Stack:
- ToolLoopAgent (ai@7) + OpenRouter (OPENROUTER_API_KEY), model via LH_MODEL,
  default anthropic/claude-sonnet-4.5 with reasoning tokens
- quiz/ask_user_question = client-side tools (no server execute): the call
  lands as a typed tool part in input-available state; the card grades via
  src/core/question-core.ts; addToolOutput sends the verdict; the teacher's
  reaction continues the same assistant message
- resume-mid-quiz is free: the pending tool part persists in the transcript
- persistence: one JSON per chat (data/chats/), full UIMessage transcripts,
  saved onFinish (also on abort)
- UI: AI Elements (owned copy-paste components, pruned to the five in use)
  + button-based QuizCard/AnsweredCard (ask answers never graded)
- pi fully removed: TUI, extensions, Fastify+WS server, bridge, custom
  protocol all deleted (recoverable from git history)
- tests: question-core units carry over; chat-flow integration drives
  handleChatRequest with MockLanguageModelV4 (48 tests, zero tokens);
  render smoke tests guard the cards (renderToStaticMarkup)

Carried over unchanged: teacher system prompt, question-core, schema/
ledger/derive/extract pipeline, data model.

components/ai-elements/conversation.tsx

@@ -0,0 +1,168 @@
+"use client";
+
+import { Button } from "@/components/ui/button";
+import { cn } from "@/lib/utils";
+import type { UIMessage } from "ai";
+import { ArrowDownIcon, DownloadIcon } from "lucide-react";
+import type { ComponentProps } from "react";
+import { useCallback } from "react";
+import { StickToBottom, useStickToBottomContext } from "use-stick-to-bottom";
+
+export type ConversationProps = ComponentProps<typeof StickToBottom>;
+
+export const Conversation = ({ className, ...props }: ConversationProps) => (
+  <StickToBottom
+    className={cn("relative flex-1 overflow-y-hidden", className)}
+    initial="smooth"
+    resize="smooth"
+    role="log"
+    {...props}
+  />
+);
+
+export type ConversationContentProps = ComponentProps<
+  typeof StickToBottom.Content
+>;
+
+export const ConversationContent = ({
+  className,
+  ...props
+}: ConversationContentProps) => (
+  <StickToBottom.Content
+    className={cn("flex flex-col gap-8 p-4", className)}
+    {...props}
+  />
+);
+
+export type ConversationEmptyStateProps = ComponentProps<"div"> & {
+  title?: string;
+  description?: string;
+  icon?: React.ReactNode;
+};
+
+export const ConversationEmptyState = ({
+  className,
+  title = "No messages yet",
+  description = "Start a conversation to see messages here",
+  icon,
+  children,
+  ...props
+}: ConversationEmptyStateProps) => (
+  <div
+    className={cn(
+      "flex size-full flex-col items-center justify-center gap-3 p-8 text-center",
+      className
+    )}
+    {...props}
+  >
+    {children ?? (
+      <>
+        {icon && <div className="text-muted-foreground">{icon}</div>}
+        <div className="space-y-1">
+          <h3 className="font-medium text-sm">{title}</h3>
+          {description && (
+            <p className="text-muted-foreground text-sm">{description}</p>
+          )}
+        </div>
+      </>
+    )}
+  </div>
+);
+
+export type ConversationScrollButtonProps = ComponentProps<typeof Button>;
+
+export const ConversationScrollButton = ({
+  className,
+  ...props
+}: ConversationScrollButtonProps) => {
+  const { isAtBottom, scrollToBottom } = useStickToBottomContext();
+
+  const handleScrollToBottom = useCallback(() => {
+    scrollToBottom();
+  }, [scrollToBottom]);
+
+  return (
+    !isAtBottom && (
+      <Button
+        className={cn(
+          "absolute bottom-4 left-[50%] translate-x-[-50%] rounded-full dark:bg-background dark:hover:bg-muted",
+          className
+        )}
+        onClick={handleScrollToBottom}
+        size="icon"
+        type="button"
+        variant="outline"
+        {...props}
+      >
+        <ArrowDownIcon className="size-4" />
+      </Button>
+    )
+  );
+};
+
+const getMessageText = (message: UIMessage): string =>
+  message.parts
+    .filter((part) => part.type === "text")
+    .map((part) => part.text)
+    .join("");
+
+export type ConversationDownloadProps = Omit<
+  ComponentProps<typeof Button>,
+  "onClick"
+> & {
+  messages: UIMessage[];
+  filename?: string;
+  formatMessage?: (message: UIMessage, index: number) => string;
+};
+
+const defaultFormatMessage = (message: UIMessage): string => {
+  const roleLabel =
+    message.role.charAt(0).toUpperCase() + message.role.slice(1);
+  return `**${roleLabel}:** ${getMessageText(message)}`;
+};
+
+export const messagesToMarkdown = (
+  messages: UIMessage[],
+  formatMessage: (
+    message: UIMessage,
+    index: number
+  ) => string = defaultFormatMessage
+): string => messages.map((msg, i) => formatMessage(msg, i)).join("\n\n");
+
+export const ConversationDownload = ({
+  messages,
+  filename = "conversation.md",
+  formatMessage = defaultFormatMessage,
+  className,
+  children,
+  ...props
+}: ConversationDownloadProps) => {
+  const handleDownload = useCallback(() => {
+    const markdown = messagesToMarkdown(messages, formatMessage);
+    const blob = new Blob([markdown], { type: "text/markdown" });
+    const url = URL.createObjectURL(blob);
+    const link = document.createElement("a");
+    link.href = url;
+    link.download = filename;
+    document.body.append(link);
+    link.click();
+    link.remove();
+    URL.revokeObjectURL(url);
+  }, [messages, filename, formatMessage]);
+
+  return (
+    <Button
+      className={cn(
+        "absolute top-4 right-4 rounded-full dark:bg-background dark:hover:bg-muted",
+        className
+      )}
+      onClick={handleDownload}
+      size="icon"
+      type="button"
+      variant="outline"
+      {...props}
+    >
+      {children ?? <DownloadIcon className="size-4" />}
+    </Button>
+  );
+};