chore: import upstream snapshot with attribution

docs/app/api/docs-chat/route.ts

@@ -0,0 +1,163 @@
+import { NextResponse } from "next/server";
+import { convertToModelMessages, stepCountIs, streamText } from "ai";
+import type { ModelMessage, UIMessage } from "ai";
+import { createBashTool } from "bash-tool";
+import { docs } from "@/lib/docs";
+import { readArticleBySlug } from "@/lib/articles";
+import {
+  docsChatDailyRateLimit,
+  docsChatMinuteRateLimit,
+  isDocsChatRateLimitConfigured,
+} from "@/lib/rate-limit";
+
+export const maxDuration = 60;
+
+const DEFAULT_MODEL = "anthropic/claude-haiku-4.5";
+
+const SYSTEM_PROMPT = `You are a helpful documentation assistant for Zero, a pre-1 experimental programming language project exploring agent-first design. Zero intentionally makes breaking changes while searching for the language, library, and tooling patterns that work best for agents. Security vulnerabilities should be expected; Zero should be run or developed only in safe, non-production environments.
+
+GitHub repository: https://github.com/vercel-labs/zerolang
+Documentation: https://zerolang.ai
+
+You have access to the full Zero documentation via the bash and readFile tools. The docs are available as markdown files in the /workspace/ directory. The file layout matches each page's URL slug — e.g. /workspace/index.md is the home, /workspace/getting-started.md is /getting-started, /workspace/modules/parse.md is /modules/parse.
+
+When answering questions:
+- Use the bash tool to list files (ls /workspace/) or search for content (grep -r "keyword" /workspace/)
+- Use the readFile tool to read specific documentation pages (e.g. readFile with path "/workspace/getting-started.md")
+- Do NOT use bash to write, create, modify, or delete files (no tee, cat >, sed -i, echo >, cp, mv, rm, mkdir, touch, etc.) — you are read-only
+- Always base your answers on the actual documentation content
+- Be concise and accurate
+- If the docs don't cover a topic, say so honestly
+- Do NOT include source references or file paths in your response
+- Do NOT use emojis in your responses
+- When showing Zero projection syntax, use \`\`\`zero fenced blocks and say it is a human-readable projection of the graph. When showing shell commands, use \`\`\`sh.`;
+
+type DocsFiles = Record<string, string>;
+
+let cachedDocsFiles: DocsFiles | null = null;
+
+async function loadDocsFiles(): Promise<DocsFiles> {
+  if (cachedDocsFiles) return cachedDocsFiles;
+
+  const files: DocsFiles = {};
+  const results = await Promise.allSettled(
+    docs.map(async (doc) => {
+      const md = await readArticleBySlug(doc.slug);
+      if (!md) return null;
+      const fileName = doc.path === "/" ? "/index.md" : `${doc.path}.md`;
+      return { fileName: fileName.replace(/^\//, ""), md };
+    }),
+  );
+  for (const result of results) {
+    if (result.status === "fulfilled" && result.value) {
+      files[result.value.fileName] = result.value.md;
+    }
+  }
+  cachedDocsFiles = files;
+  return files;
+}
+
+function addCacheControl(messages: ModelMessage[]): ModelMessage[] {
+  if (messages.length === 0) return messages;
+  return messages.map((message, index) => {
+    if (index === messages.length - 1) {
+      return {
+        ...message,
+        providerOptions: {
+          ...message.providerOptions,
+          anthropic: { cacheControl: { type: "ephemeral" } },
+        },
+      };
+    }
+    return message;
+  });
+}
+
+function getRateLimitIdentifier(req: Request): string {
+  const forwardedFor = req.headers.get("x-forwarded-for");
+  const realIp = req.headers.get("x-real-ip");
+  return forwardedFor?.split(",")[0]?.trim() || realIp?.trim() || "anonymous";
+}
+
+async function rateLimitRequest(req: Request): Promise<NextResponse | null> {
+  if (!isDocsChatRateLimitConfigured()) {
+    return NextResponse.json(
+      {
+        error: "Chat rate limiting is not configured",
+        message: "Set KV_REST_API_URL and KV_REST_API_TOKEN to enable docs chat.",
+      },
+      { status: 503 },
+    );
+  }
+
+  const identifier = getRateLimitIdentifier(req);
+  let minuteResult;
+  let dailyResult;
+  try {
+    [minuteResult, dailyResult] = await Promise.all([
+      docsChatMinuteRateLimit.limit(identifier),
+      docsChatDailyRateLimit.limit(identifier),
+    ]);
+  } catch (error) {
+    console.error("Docs chat rate limiting failed", error);
+    return NextResponse.json(
+      {
+        error: "Chat rate limiting unavailable",
+        message: "Docs chat is temporarily unavailable because rate limiting could not be applied.",
+      },
+      { status: 503 },
+    );
+  }
+
+  if (minuteResult.success && dailyResult.success) return null;
+
+  const isMinuteLimit = !minuteResult.success;
+  return NextResponse.json(
+    {
+      error: "Rate limit exceeded",
+      message: isMinuteLimit
+        ? "Too many requests. Please wait a moment before trying again."
+        : "Daily limit reached. Please try again tomorrow.",
+    },
+    { status: 429 },
+  );
+}
+
+export async function POST(req: Request) {
+  if (!process.env.AI_GATEWAY_API_KEY && !process.env.VERCEL_OIDC_TOKEN) {
+    return NextResponse.json(
+      { error: "Chat is not configured. Set AI_GATEWAY_API_KEY or configure deployment OIDC." },
+      { status: 503 },
+    );
+  }
+
+  const rateLimitResponse = await rateLimitRequest(req);
+  if (rateLimitResponse) return rateLimitResponse;
+
+  let body: { messages?: UIMessage[] } | null;
+  try {
+    body = (await req.json()) as { messages?: UIMessage[] };
+  } catch {
+    return NextResponse.json({ error: "Invalid JSON body" }, { status: 400 });
+  }
+
+  const messages = Array.isArray(body?.messages) ? body.messages : [];
+
+  const docsFiles = await loadDocsFiles();
+  const {
+    tools: { bash, readFile },
+  } = await createBashTool({ files: docsFiles });
+
+  const result = streamText({
+    model: DEFAULT_MODEL,
+    system: SYSTEM_PROMPT,
+    messages: await convertToModelMessages(messages),
+    stopWhen: stepCountIs(5),
+    tools: { bash, readFile },
+    prepareStep: ({ messages: stepMessages }) => ({
+      messages: addCacheControl(stepMessages),
+    }),
+  });
+
+  return result.toUIMessageStreamResponse();
+}