fix(studio): poll background generation and handle gateway failures

packages/design-studio/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@wrnexus/design-studio",
-  "version": "0.1.6",
+  "version": "0.1.7",
   "private": true,
   "type": "module",
   "main": "src/index.ts",

packages/design-studio/src/generation-transport.ts

@@ -0,0 +1,72 @@
+/** Read gateway failures without exposing an HTML error page as a JSON parse error. */
+export async function generationResponse(response: Response): Promise<any> {
+  const text = await response.text();
+  let value: any;
+  try {
+    value = JSON.parse(text);
+  } catch {
+    throw Error(
+      [502, 503, 504].includes(response.status)
+        ? `The deployment gateway could not complete this request (HTTP ${response.status}). Try again shortly.`
+        : `The generation server returned an unreadable response (HTTP ${response.status}). Reload after deploying the latest server.`,
+    );
+  }
+  if (!response.ok)
+    throw Error(
+      typeof value?.error === "string"
+        ? value.error
+        : `Generation request failed (HTTP ${response.status}).`,
+    );
+  return value;
+}
+
+export async function requestGeneration(
+  url: URL,
+  input: unknown,
+  signal: AbortSignal,
+  transport: typeof fetch = fetch,
+) {
+  let jobUrl: URL | undefined;
+  const deadline = AbortSignal.any([signal, AbortSignal.timeout(75_000)]);
+  try {
+    let result = await generationResponse(
+      await transport(url, {
+        method: "POST",
+        headers: { "content-type": "application/json", prefer: "respond-async" },
+        body: JSON.stringify(input),
+        signal: deadline,
+      }),
+    );
+    if (!result.job) return result; // Compatible with local engines and older synchronous servers.
+    if (typeof result.job.id !== "string" || !/^[a-f0-9-]{36}$/.test(result.job.id))
+      throw Error("Invalid generation job response.");
+    jobUrl = new URL(url.href.replace(/\/$/, "") + "/jobs/" + result.job.id);
+    while (true) {
+      await new Promise<void>((resolve, reject) => {
+        const aborted = () => {
+          clearTimeout(timer);
+          reject(deadline.reason);
+        };
+        const timer = setTimeout(() => {
+          deadline.removeEventListener("abort", aborted);
+          resolve();
+        }, 1000);
+        if (deadline.aborted) aborted();
+        else deadline.addEventListener("abort", aborted, { once: true });
+      });
+      result = await generationResponse(
+        await transport(jobUrl, { signal: deadline, cache: "no-store" }),
+      );
+      if (result.status === "complete") return result.result;
+      if (result.status === "failed" || result.status === "cancelled")
+        throw Error(result.error ?? "Generation did not complete.");
+      if (result.status !== "pending") throw Error("Invalid generation job status.");
+    }
+  } finally {
+    if (jobUrl && deadline.aborted) {
+      void transport(jobUrl, { method: "DELETE", signal: AbortSignal.timeout(3000) }).catch(
+        () => {},
+      );
+    }
+  }
+}

packages/design-studio/src/guidance.ts

@@ -1,3 +1,4 @@
+import { requestGeneration } from "./generation-transport.ts";
 import {
   DEFAULT_DESIGN_BRIEF,
   type DesignBrief,
@@ -280,21 +281,18 @@ export function setupGuidance(
     render();
     try {
       await hooks.review?.(undefined);
-      const response = await fetch(new URL("./api/generate", document.baseURI), {
-        method: "POST",
-        headers: { "content-type": "application/json" },
-        body: JSON.stringify({
+      const result = await requestGeneration(
+        new URL("./api/generate", document.baseURI),
+        {
           system,
           locks,
           brief: requestedBrief,
           baseRevision,
           kind,
           instruction: kind === "edit" ? value("edit-instruction").value : undefined,
-        }),
+        },
         signal,
-      });
-      const result = await response.json();
-      if (!response.ok) throw Error(result.error ?? "Generation failed.");
+      );
       if (current !== epoch || signal.aborted) return;
       if (result.diagnostics.length) {
         status =

packages/design-studio/test/generation-transport.test.ts

@@ -0,0 +1,66 @@
+import { expect, test } from "bun:test";
+import { generationResponse, requestGeneration } from "../src/generation-transport.ts";
+
+test("HTML gateway failures produce a clear diagnostic rather than a JSON syntax error", async () => {
+  for (const status of [502, 503, 504])
+    await expect(
+      generationResponse(new Response("<html>Gateway error</html>", { status })),
+    ).rejects.toThrow(`HTTP ${status}`);
+  await expect(
+    generationResponse(new Response("<html>private proxy text</html>", { status: 504 })),
+  ).rejects.not.toThrow("private proxy text");
+});
+test("generation uses short job polls and preserves legacy response compatibility", async () => {
+  const batch = { alternatives: [1, 2, 3], diagnostics: [] };
+  let calls = 0;
+  const transport = (async (_url: unknown, init?: RequestInit) => {
+    calls++;
+    if (calls === 1) {
+      expect(new Headers(init?.headers).get("prefer")).toBe("respond-async");
+      return Response.json(
+        { job: { id: "11111111-1111-4111-8111-111111111111" } },
+        { status: 202 },
+      );
+    }
+    expect(init?.method).toBeUndefined();
+    return Response.json({ status: "complete", result: batch });
+  }) as unknown as typeof fetch;
+  expect(
+    await requestGeneration(
+      new URL("https://example.test/design-studio/api/generate"),
+      {},
+      new AbortController().signal,
+      transport,
+    ),
+  ).toEqual(batch);
+  expect(calls).toBe(2);
+  expect(
+    await requestGeneration(
+      new URL("https://example.test/api/generate"),
+      {},
+      new AbortController().signal,
+      (async () => Response.json(batch)) as unknown as typeof fetch,
+    ),
+  ).toEqual(batch);
+});
+test("cancelling a pending job sends cancellation without replacing a draft", async () => {
+  const controller = new AbortController();
+  let cancelled = false;
+  const transport = (async (_url: unknown, init?: RequestInit) => {
+    if (init?.method === "DELETE") {
+      cancelled = true;
+      return Response.json({ status: "cancelled" });
+    }
+    controller.abort();
+    return Response.json({ job: { id: "11111111-1111-4111-8111-111111111111" } }, { status: 202 });
+  }) as unknown as typeof fetch;
+  await expect(
+    requestGeneration(
+      new URL("https://example.test/api/generate"),
+      {},
+      controller.signal,
+      transport,
+    ),
+  ).rejects.toBeDefined();
+  expect(cancelled).toBe(true);
+});