cloudflare__vinext/tests/app-page-execution.test.ts

import { describe, expect, it, vi } from "vite-plus/test";
import {
  buildAppPageFontLinkHeader,
  buildAppPageSpecialErrorResponse,
  probeAppPageComponent,
  probeAppPageLayouts,
  resolveAppPageSpecialError,
  teeAppPageRscStreamForCapture,
} from "../packages/vinext/src/server/app-page-execution.js";
import { readStreamAsText } from "../packages/vinext/src/utils/text-stream.js";

function createStream(chunks: string[]): ReadableStream<Uint8Array> {
  return new ReadableStream({
    start(controller) {
      for (const chunk of chunks) {
        controller.enqueue(new TextEncoder().encode(chunk));
      }
      controller.close();
    },
  });
}

function createMiddlewareContext() {
  const headers = new Headers();
  headers.set("x-middleware-security", "present");
  headers.append("set-cookie", "session=rotated; Path=/; HttpOnly");
  headers.set("vary", "x-auth-state");

  return {
    headers,
    status: 299,
  };
}

describe("app page execution helpers", () => {
  it("parses redirect and access-fallback digests", () => {
    expect(
      resolveAppPageSpecialError({
        digest: "NEXT_REDIRECT;replace;%2Fredirected;308",
      }),
    ).toEqual({
      kind: "redirect",
      location: "/redirected",
      statusCode: 308,
    });

    expect(
      resolveAppPageSpecialError({
        digest: "NEXT_HTTP_ERROR_FALLBACK;403",
      }),
    ).toEqual({
      kind: "http-access-fallback",
      statusCode: 403,
    });

    expect(resolveAppPageSpecialError({ digest: "not-special" })).toBeNull();
  });

  it("builds redirect and fallback responses while preserving fallback context behavior", async () => {
    const clearRequestContext = vi.fn();

    const redirectResponse = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      isRscRequest: false,
      middlewareContext: createMiddlewareContext(),
      request: new Request("https://example.com/start"),
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
      },
    });

    expect(redirectResponse.status).toBe(307);
    expect(redirectResponse.headers.get("location")).toBe("https://example.com/redirected");
    expect(redirectResponse.headers.get("x-middleware-security")).toBe("present");
    expect(redirectResponse.headers.get("vary")).toBe("x-auth-state");
    expect(redirectResponse.headers.getSetCookie()).toContain("session=rotated; Path=/; HttpOnly");
    expect(clearRequestContext).toHaveBeenCalledTimes(1);

    clearRequestContext.mockClear();

    const fallbackResponse = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      isRscRequest: false,
      middlewareContext: createMiddlewareContext(),
      renderFallbackPage(statusCode) {
        return Promise.resolve(
          new Response(`fallback:${statusCode}`, {
            headers: { Vary: "RSC, Accept" },
            status: statusCode,
          }),
        );
      },
      request: new Request("https://example.com/start"),
      specialError: {
        kind: "http-access-fallback",
        statusCode: 404,
      },
    });

    expect(fallbackResponse.status).toBe(404);
    expect(fallbackResponse.headers.get("x-middleware-security")).toBe("present");
    expect(fallbackResponse.headers.get("vary")).toBe("RSC, Accept, x-auth-state");
    expect(fallbackResponse.headers.getSetCookie()).toContain("session=rotated; Path=/; HttpOnly");
    expect(
      fallbackResponse.headers
        .getSetCookie()
        .filter((cookie) => cookie === "session=rotated; Path=/; HttpOnly"),
    ).toHaveLength(1);
    await expect(fallbackResponse.text()).resolves.toBe("fallback:404");
    expect(clearRequestContext).not.toHaveBeenCalled();
  });

  it("prefixes redirect Location with basePath for app-internal paths", async () => {
    // Mirrors Next.js's `addPathPrefix(getURLFromRedirectError(err), basePath)`.
    // `redirect("/about")` from a page mounted under basePath "/blog" should
    // produce `Location: https://example.com/blog/about`, not the raw "/about".
    const clearRequestContext = vi.fn();

    const internalRedirect = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "/about",
        statusCode: 307,
      },
    });

    expect(internalRedirect.headers.get("location")).toBe("https://example.com/blog/about");

    // External redirects (different origin) must NOT be prefixed — they're
    // outside the app's basePath scope.
    const externalRedirect = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "https://other.example/foo",
        statusCode: 307,
      },
    });

    expect(externalRedirect.headers.get("location")).toBe("https://other.example/foo");

    // Targets that already include the basePath prefix must be left alone
    // (caller already did the work or middleware-driven redirect).
    const alreadyPrefixed = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "/blog/about",
        statusCode: 307,
      },
    });

    expect(alreadyPrefixed.headers.get("location")).toBe("https://example.com/blog/about");

    const alreadyPrefixedRootWithQuery = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "/blog?from=checkout",
        statusCode: 307,
      },
    });

    expect(alreadyPrefixedRootWithQuery.headers.get("location")).toBe(
      "https://example.com/blog?from=checkout",
    );

    const alreadyPrefixedRootWithHash = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "/blog#top",
        statusCode: 307,
      },
    });

    expect(alreadyPrefixedRootWithHash.headers.get("location")).toBe(
      "https://example.com/blog#top",
    );

    // No basePath configured → behavior unchanged (resolves against the
    // request URL as before).
    const unconfigured = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/protected"),
      specialError: {
        kind: "redirect",
        location: "/about",
        statusCode: 307,
      },
    });

    expect(unconfigured.headers.get("location")).toBe("https://example.com/about");

    // Redirect to root ("/") under basePath should land on the basePath itself,
    // not "/blog/" with a trailing slash artifact.
    const rootRedirect = await buildAppPageSpecialErrorResponse({
      basePath: "/blog",
      clearRequestContext,
      isRscRequest: false,
      request: new Request("https://example.com/blog/protected"),
      specialError: {
        kind: "redirect",
        location: "/",
        statusCode: 307,
      },
    });

    expect(rootRedirect.headers.get("location")).toBe("https://example.com/blog");
  });

  it("appends pending cookies (cookies().set during render) to redirect responses", async () => {
    // Mirrors Next.js's `appendMutableCookies(headers, requestStore.mutableCookies)`
    // in app-render.tsx. An auth flow that does
    //   cookies().set("session", "...");
    //   redirect("/dashboard");
    // must keep the Set-Cookie on the 307 — otherwise the redirected
    // request lands without the just-issued session and the user bounces
    // back to login.
    const clearRequestContext = vi.fn();
    const getAndClearPendingCookies = vi.fn(() => [
      "session=fresh; Path=/; HttpOnly",
      "csrf=abc; Path=/",
    ]);

    const redirectWithCookies = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      getAndClearPendingCookies,
      isRscRequest: false,
      request: new Request("https://example.com/login"),
      specialError: {
        kind: "redirect",
        location: "/dashboard",
        statusCode: 307,
      },
    });

    expect(redirectWithCookies.status).toBe(307);
    expect(redirectWithCookies.headers.get("location")).toBe("https://example.com/dashboard");
    const setCookies = redirectWithCookies.headers.getSetCookie();
    expect(setCookies).toContain("session=fresh; Path=/; HttpOnly");
    expect(setCookies).toContain("csrf=abc; Path=/");
    expect(getAndClearPendingCookies).toHaveBeenCalledTimes(1);

    // No accumulated cookies → no Set-Cookie header (and the accumulator
    // is still consulted exactly once).
    getAndClearPendingCookies.mockReturnValue([]);
    const redirectWithoutCookies = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      getAndClearPendingCookies,
      isRscRequest: false,
      request: new Request("https://example.com/login"),
      specialError: {
        kind: "redirect",
        location: "/dashboard",
        statusCode: 307,
      },
    });

    expect(redirectWithoutCookies.headers.getSetCookie()).toEqual([]);

    // Pending cookies must NOT bleed onto http-access-fallback responses —
    // those cookies belong to the rendered boundary, not the bare 401/403/404.
    // Matches Next.js, which only calls appendMutableCookies in the redirect
    // branch.
    getAndClearPendingCookies.mockReturnValue(["should-not-appear=1; Path=/"]);
    const fallbackResponse = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      getAndClearPendingCookies,
      isRscRequest: false,
      request: new Request("https://example.com/protected"),
      specialError: {
        kind: "http-access-fallback",
        statusCode: 401,
      },
    });

    expect(fallbackResponse.headers.getSetCookie()).toEqual([]);
  });

  it("falls back to a plain status response when no fallback page is available", async () => {
    const clearRequestContext = vi.fn();

    const response = await buildAppPageSpecialErrorResponse({
      clearRequestContext,
      isRscRequest: false,
      middlewareContext: createMiddlewareContext(),
      renderFallbackPage() {
        return Promise.resolve(null);
      },
      request: new Request("https://example.com/start"),
      specialError: {
        kind: "http-access-fallback",
        statusCode: 401,
      },
    });

    expect(response.status).toBe(401);
    expect(response.headers.get("x-middleware-security")).toBe("present");
    expect(response.headers.get("vary")).toBe("x-auth-state");
    expect(response.headers.getSetCookie()).toContain("session=rotated; Path=/; HttpOnly");
    await expect(response.text()).resolves.toBe("Unauthorized");
    expect(clearRequestContext).toHaveBeenCalledTimes(1);
  });

  it("encodes redirect digest in flight payload + 200 when buildRscRedirectFlightStream is provided (RSC request)", async () => {
    // Mirrors Next.js's `generateDynamicFlightRenderResult` path: when a
    // server component throws redirect() during RSC rendering, the redirect
    // digest is serialized into the flight stream and the response stays
    // 200. The status line never carries the redirect.
    //
    // See: https://github.com/cloudflare/vinext/issues/1347
    const buildRscRedirectFlightStream = vi.fn(
      (options: { digest: string }) =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode(`E:${options.digest}`));
            controller.close();
          },
        }),
    );

    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream,
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
      },
    });

    expect(response.status).toBe(200);
    expect(response.headers.get("content-type")).toMatch(/^text\/x-component/);
    expect(response.headers.get("location")).toBeNull();
    expect(buildRscRedirectFlightStream).toHaveBeenCalledTimes(1);
    expect(buildRscRedirectFlightStream).toHaveBeenCalledWith({
      digest: "NEXT_REDIRECT;replace;/redirected;307;",
    });
    await expect(response.text()).resolves.toBe("E:NEXT_REDIRECT;replace;/redirected;307;");
  });

  it("keeps metadata-originated RSC redirects on the Flight digest path", async () => {
    // Ported from Next.js:
    // test/e2e/app-dir/metadata-streaming/metadata-streaming.test.ts
    //   "should trigger redirection when call redirect"
    //
    // Document requests and RSC navigation requests intentionally diverge:
    // the document path streams a refresh meta tag, while the client router
    // still consumes the redirect digest from the Flight stream.
    const buildRscRedirectFlightStream = vi.fn(
      (options: { digest: string }) =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode(`E:${options.digest}`));
            controller.close();
          },
        }),
    );

    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream,
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
        fromMetadata: true,
      },
    });

    expect(response.status).toBe(200);
    expect(response.headers.get("content-type")).toMatch(/^text\/x-component/);
    expect(response.headers.get("location")).toBeNull();
    expect(buildRscRedirectFlightStream).toHaveBeenCalledTimes(1);
    expect(buildRscRedirectFlightStream).toHaveBeenCalledWith({
      digest: "NEXT_REDIRECT;replace;/redirected;307;",
    });
    await expect(response.text()).resolves.toBe("E:NEXT_REDIRECT;replace;/redirected;307;");
  });

  it("renders a metadata-originated document redirect as an HTML refresh when metadata streams", async () => {
    // Ported from Next.js:
    // test/e2e/app-dir/metadata-streaming/metadata-streaming.test.ts
    //   "should trigger redirection when call redirect"
    //
    // Next.js captures redirect() thrown by generateMetadata() as a streamed
    // server error and injects the canonical refresh meta tag through
    // make-get-server-inserted-html.tsx. The document status stays 200, but it
    // must remain an HTML document so a browser direct visit can follow it.
    const buildRscRedirectFlightStream = vi.fn(
      () =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode("flight-payload"));
            controller.close();
          },
        }),
    );

    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream,
      clearRequestContext: vi.fn(),
      isRscRequest: false,
      request: new Request("https://example.com/start"),
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
        fromMetadata: true,
      },
    });

    expect(response.status).toBe(200);
    expect(response.headers.get("content-type")).toContain("text/html");
    expect(buildRscRedirectFlightStream).not.toHaveBeenCalled();
    await expect(response.text()).resolves.toContain(
      '<meta id="__next-page-redirect" http-equiv="refresh" content="1;url=/redirected"/>',
    );
  });

  it("uses an HTTP redirect for metadata-originated redirects when metadata streaming is disabled", async () => {
    // Ported from Next.js:
    // test/e2e/app-dir/metadata-streaming/metadata-streaming.test.ts
    //   "should render blocking 307 response status when html limited bots access redirect"
    const buildRscRedirectFlightStream = vi.fn(
      () =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode("flight-payload"));
            controller.close();
          },
        }),
    );

    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream,
      clearRequestContext: vi.fn(),
      isRscRequest: false,
      request: new Request("https://example.com/start"),
      serveStreamingMetadata: false,
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
        fromMetadata: true,
      },
    });

    expect(response.status).toBe(307);
    expect(response.headers.get("location")).toBe("https://example.com/redirected");
    expect(buildRscRedirectFlightStream).not.toHaveBeenCalled();
  });

  it("preserves the 307/308 status code in the encoded digest (permanentRedirect)", async () => {
    const captured: { digest: string }[] = [];
    const buildRscRedirectFlightStream = (opts: { digest: string }) => {
      captured.push(opts);
      return new ReadableStream<Uint8Array>({
        start(controller) {
          controller.close();
        },
      });
    };

    await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream,
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: {
        kind: "redirect",
        location: "/permanent-target",
        statusCode: 308,
      },
    });

    expect(captured).toEqual([{ digest: "NEXT_REDIRECT;replace;/permanent-target;308;" }]);
  });

  it("falls back to 307 when buildRscRedirectFlightStream is absent (backward compat)", async () => {
    // Callers that don't yet plumb the flight-stream builder keep the legacy
    // behavior: HTTP 307 with a Location header. Keeps non-app-router callers
    // (and any test helpers) working without changes.
    const response = await buildAppPageSpecialErrorResponse({
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: {
        kind: "redirect",
        location: "/redirected",
        statusCode: 307,
      },
    });

    expect(response.status).toBe(307);
    expect(response.headers.get("location")).toMatch(/redirected\?_rsc/);
  });

  it("canonicalizes same-origin RSC redirect locations to Next-style RSC URLs", async () => {
    const response = await buildAppPageSpecialErrorResponse({
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc", {
        headers: {
          Accept: "text/x-component",
          RSC: "1",
          "Next-Router-State-Tree": "tree",
        },
      }),
      specialError: {
        kind: "redirect",
        location: "/redirected?tab=1",
        statusCode: 307,
      },
    });

    expect(response.status).toBe(307);
    expect(response.headers.get("location")).toMatch(
      /^https:\/\/example\.com\/redirected\?tab=1&_rsc=/,
    );
  });

  it("probes layouts from inner to outer and stops on a handled special response", async () => {
    const probedLayouts: number[] = [];

    const result = await probeAppPageLayouts({
      layoutCount: 3,
      async onLayoutError(error, layoutIndex) {
        expect(error).toBeInstanceOf(Error);
        return layoutIndex === 1 ? new Response("layout-fallback", { status: 404 }) : null;
      },
      probeLayoutAt(layoutIndex) {
        probedLayouts.push(layoutIndex);
        if (layoutIndex === 1) {
          throw new Error("layout failed");
        }
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
    });

    expect(probedLayouts).toEqual([2, 1]);
    expect(result.response?.status).toBe(404);
    await expect(result.response?.text()).resolves.toBe("layout-fallback");
  });

  it("does not await async page probes when a loading boundary is present", async () => {
    const onError = vi.fn();

    const response = await probeAppPageComponent({
      awaitAsyncResult: false,
      onError,
      probePage() {
        return new Promise<void>(() => {});
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
    });

    expect(response).toBeNull();
    expect(onError).not.toHaveBeenCalled();
  });

  it("produces fused ssrStream + sideStream when capturing (#981)", async () => {
    const capture = teeAppPageRscStreamForCapture(createStream(["flight-", "chunk"]), true);

    // ssrStream is for createFromReadableStream (SSR)
    expect(capture.ssrStream).toBeInstanceOf(ReadableStream);
    // sideStream is for embed+capture
    expect(capture.sideStream).toBeInstanceOf(ReadableStream);

    // Both streams should contain identical data (teed from same source)
    const ssrText = await readStreamAsText(capture.ssrStream);
    const sideText = await readStreamAsText(capture.sideStream!);
    expect(ssrText).toBe("flight-chunk");
    expect(sideText).toBe("flight-chunk");
  });

  it("bypasses tee when not capturing (#981)", async () => {
    const stream = createStream(["no-capture"]);
    const capture = teeAppPageRscStreamForCapture(stream, false);

    // When not capturing, no tee — the original stream is returned as ssrStream
    expect(capture.ssrStream).toBe(stream);
    expect(capture.sideStream).toBeUndefined();
  });

  it("tracks per-layout dynamic usage when classification options are provided", async () => {
    const result = await probeAppPageLayouts({
      layoutCount: 3,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [2, "dynamic"],
        ]),
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/blog", "layout:/blog/post"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          return Promise.resolve({ result: fn(), dynamicDetected: false });
        },
      },
    });

    expect(result.response).toBeNull();
    // Layout 0 is build-time static, layout 2 is build-time dynamic
    // Layout 1 has no build-time classification, probed with no dynamic detected
    expect(result.layoutFlags).toEqual({
      "layout:/": "s",
      "layout:/blog": "s",
      "layout:/blog/post": "d",
    });
  });

  it("detects dynamic usage per-layout through isolated scope", async () => {
    let probeCallCount = 0;
    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          probeCallCount++;
          const result = fn();
          // Simulate: second probe call (layout 0, since we iterate inner-to-outer)
          // detects dynamic usage
          return Promise.resolve({
            result,
            dynamicDetected: probeCallCount === 2,
          });
        },
      },
    });

    expect(result.response).toBeNull();
    expect(result.layoutFlags).toEqual({
      "layout:/": "d",
      "layout:/dashboard": "s",
    });
  });

  it("returns empty layoutFlags when classification options are absent (backward compat)", async () => {
    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
    });

    expect(result.response).toBeNull();
    expect(result.layoutFlags).toEqual({});
  });

  it("defaults to dynamic flag when probe throws a non-special error", async () => {
    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        // Non-special error — return null (don't short-circuit)
        return Promise.resolve(null);
      },
      probeLayoutAt(layoutIndex) {
        if (layoutIndex === 1) throw new Error("use() outside render");
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          // Re-throw so the catch path in probeAppPageLayouts fires
          return Promise.resolve(fn()).then((result) => ({ result, dynamicDetected: false }));
        },
      },
    });

    expect(result.response).toBeNull();
    // Layout 1 threw → conservatively flagged as dynamic
    expect(result.layoutFlags["layout:/dashboard"]).toBe("d");
    // Layout 0 probed successfully
    expect(result.layoutFlags["layout:/"]).toBe("s");
  });

  it("isolates dynamic usage across throwing layout probes", async () => {
    let dynamicUsageDetected = false;

    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt(layoutIndex) {
        if (layoutIndex === 1) {
          dynamicUsageDetected = true;
          throw new Error("layout failed after headers()");
        }
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        async runWithIsolatedDynamicScope(fn) {
          const priorDynamic = dynamicUsageDetected;
          dynamicUsageDetected = false;
          try {
            const result = await fn();
            const detectedInScope = dynamicUsageDetected;
            dynamicUsageDetected = false;
            return { result, dynamicDetected: detectedInScope };
          } finally {
            dynamicUsageDetected = false;
            if (priorDynamic) dynamicUsageDetected = true;
          }
        },
      },
    });

    expect(result.response).toBeNull();
    expect(result.layoutFlags).toEqual({
      "layout:/": "s",
      "layout:/dashboard": "d",
    });
  });

  it("skips probe for build-time classified layouts", async () => {
    let probeCalls = 0;
    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [1, "dynamic"],
        ]),
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/admin"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          probeCalls++;
          return Promise.resolve({ result: fn(), dynamicDetected: false });
        },
      },
    });

    expect(probeCalls).toBe(0);
    expect(result.layoutFlags).toEqual({
      "layout:/": "s",
      "layout:/admin": "d",
    });
  });

  it("returns special error response when build-time classified layout throws during error probe", async () => {
    const layoutError = new Error("layout failed");
    const specialResponse = new Response("layout-fallback", { status: 404 });

    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError(error) {
        return Promise.resolve(error === layoutError ? specialResponse : null);
      },
      probeLayoutAt(layoutIndex) {
        if (layoutIndex === 1) throw layoutError;
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [1, "static"],
        ]),
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/admin"][layoutIndex];
        },
        runWithIsolatedDynamicScope() {
          throw new Error("isolated scope must not run for build-time classified layouts");
        },
      },
    });

    // The special-error response from the throwing layout short-circuits the
    // loop. The flag for layout 1 is still recorded (set before the error
    // probe runs), and layout 0 is never reached.
    expect(result.response).toBe(specialResponse);
    expect(result.layoutFlags).toEqual({ "layout:/admin": "s" });
  });

  it("does not read build-time reasons when debugClassification is absent", async () => {
    const throwingReasons = {
      get() {
        throw new Error("build-time reasons should stay dormant when debug is disabled");
      },
    } as unknown as ReadonlyMap<number, { layer: "segment-config"; key: "dynamic"; value: string }>;

    await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [1, "dynamic"],
        ]),
        buildTimeReasons: throwingReasons,
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/admin"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          return Promise.resolve({ result: fn(), dynamicDetected: false });
        },
      },
    });
  });

  it("emits a debug reason per layout when debugClassification is provided with build-time reasons", async () => {
    const calls: Array<{ layoutId: string; reason: unknown }> = [];

    await probeAppPageLayouts({
      layoutCount: 3,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [1, "dynamic"],
          [2, "static"],
        ]),
        buildTimeReasons: new Map([
          [0, { layer: "segment-config", key: "dynamic", value: "force-static" }],
          [1, { layer: "segment-config", key: "dynamic", value: "force-dynamic" }],
          [2, { layer: "module-graph", result: "static" }],
        ]),
        debugClassification(layoutId, reason) {
          calls.push({ layoutId, reason });
        },
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/admin", "layout:/admin/posts"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          return Promise.resolve({ result: fn(), dynamicDetected: false });
        },
      },
    });

    expect(calls).toHaveLength(3);
    const byId = Object.fromEntries(calls.map((c) => [c.layoutId, c.reason]));
    expect(byId["layout:/"]).toEqual({
      layer: "segment-config",
      key: "dynamic",
      value: "force-static",
    });
    expect(byId["layout:/admin"]).toEqual({
      layer: "segment-config",
      key: "dynamic",
      value: "force-dynamic",
    });
    expect(byId["layout:/admin/posts"]).toEqual({
      layer: "module-graph",
      result: "static",
    });
  });

  it("emits runtime-probe reason for layouts resolved by the Layer 3 probe", async () => {
    const calls: Array<{ layoutId: string; reason: unknown }> = [];
    let probeCalls = 0;

    await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        // No buildTimeClassifications → every layout takes the runtime path.
        debugClassification(layoutId, reason) {
          calls.push({ layoutId, reason });
        },
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          probeCalls++;
          // probeAppPageLayouts iterates inner-to-outer:
          // first call → layout 1 (dashboard) → dynamic
          // second call → layout 0 (root) → static
          return Promise.resolve({ result: fn(), dynamicDetected: probeCalls === 1 });
        },
      },
    });

    expect(calls).toHaveLength(2);
    const byId = Object.fromEntries(calls.map((c) => [c.layoutId, c.reason]));
    expect(byId["layout:/dashboard"]).toEqual({
      layer: "runtime-probe",
      outcome: "dynamic",
    });
    expect(byId["layout:/"]).toEqual({
      layer: "runtime-probe",
      outcome: "static",
    });
  });

  it("flips a build-time static layout to dynamic when a runtime observation is unsafe for static reuse", async () => {
    // Parity guard for the observation override: a layout the build classified
    // `static` is downgraded to `"d"` at request time when
    // `isLayoutObservationDynamic` reports the observed render is unsafe for
    // static reuse (finite revalidate, cache tags, request APIs, param scope,
    // etc.). The emitted debug reason switches from the stale build-time reason
    // to `runtime-probe`/`dynamic` so the flag and reason stay in agreement.
    const calls: Array<{ layoutId: string; reason: unknown }> = [];

    const result = await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt() {
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        buildTimeClassifications: new Map([
          [0, "static"],
          [1, "static"],
        ]),
        buildTimeReasons: new Map([
          [0, { layer: "segment-config", key: "dynamic", value: "force-static" }],
          [1, { layer: "segment-config", key: "dynamic", value: "force-static" }],
        ]),
        debugClassification(layoutId, reason) {
          calls.push({ layoutId, reason });
        },
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        // Only the dashboard layout's observation is unsafe for static reuse.
        isLayoutObservationDynamic(layoutId) {
          return layoutId === "layout:/dashboard";
        },
        runWithIsolatedDynamicScope() {
          throw new Error("isolated scope must not run for build-time classified layouts");
        },
      },
    });

    expect(result.response).toBeNull();
    // dashboard: build-time static, but the observation flips it to dynamic.
    // root: build-time static with a safe observation stays static.
    expect(result.layoutFlags).toEqual({
      "layout:/": "s",
      "layout:/dashboard": "d",
    });

    const byId = Object.fromEntries(calls.map((c) => [c.layoutId, c.reason]));
    expect(byId["layout:/dashboard"]).toEqual({
      layer: "runtime-probe",
      outcome: "dynamic",
    });
    // The unflipped layout keeps reporting its build-time reason.
    expect(byId["layout:/"]).toEqual({
      layer: "segment-config",
      key: "dynamic",
      value: "force-static",
    });
  });

  it("emits runtime-probe reason with the error message when the probe throws", async () => {
    const calls: Array<{ layoutId: string; reason: unknown }> = [];

    await probeAppPageLayouts({
      layoutCount: 2,
      onLayoutError() {
        return Promise.resolve(null);
      },
      probeLayoutAt(layoutIndex) {
        if (layoutIndex === 1) throw new Error("headers() outside render");
        return null;
      },
      runWithSuppressedHookWarning(probe) {
        return probe();
      },
      classification: {
        debugClassification(layoutId, reason) {
          calls.push({ layoutId, reason });
        },
        getLayoutId(layoutIndex) {
          return ["layout:/", "layout:/dashboard"][layoutIndex];
        },
        runWithIsolatedDynamicScope(fn) {
          return Promise.resolve(fn()).then((result) => ({ result, dynamicDetected: false }));
        },
      },
    });

    const byId = Object.fromEntries(calls.map((c) => [c.layoutId, c.reason]));
    expect(byId["layout:/dashboard"]).toEqual({
      layer: "runtime-probe",
      outcome: "dynamic",
      error: "headers() outside render",
    });
    expect(byId["layout:/"]).toEqual({
      layer: "runtime-probe",
      outcome: "static",
    });
  });

  it("builds Link headers for preloaded app-page fonts", () => {
    expect(
      buildAppPageFontLinkHeader([
        { href: "/font-a.woff2", type: "font/woff2" },
        { href: "/font-b.woff2", type: "font/woff2" },
      ]),
    ).toBe(
      "</font-a.woff2>; rel=preload; as=font; type=font/woff2; crossorigin, </font-b.woff2>; rel=preload; as=font; type=font/woff2; crossorigin",
    );
  });

  it("emits the `x-edge-runtime: 1` marker on RSC redirect flight responses for edge-runtime routes", async () => {
    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream: ({ digest }) =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode(`E:${digest}`));
            controller.close();
          },
        }),
      clearRequestContext: vi.fn(),
      isEdgeRuntime: true,
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: { kind: "redirect", location: "/redirected", statusCode: 307 },
    });

    expect(response.status).toBe(200);
    expect(response.headers.get("x-edge-runtime")).toBe("1");
  });

  it("omits the `x-edge-runtime` marker on RSC redirect flight responses for nodejs-runtime routes", async () => {
    const response = await buildAppPageSpecialErrorResponse({
      buildRscRedirectFlightStream: ({ digest }) =>
        new ReadableStream<Uint8Array>({
          start(controller) {
            controller.enqueue(new TextEncoder().encode(`E:${digest}`));
            controller.close();
          },
        }),
      clearRequestContext: vi.fn(),
      isRscRequest: true,
      request: new Request("https://example.com/start.rsc"),
      specialError: { kind: "redirect", location: "/redirected", statusCode: 307 },
    });

    expect(response.status).toBe(200);
    expect(response.headers.get("x-edge-runtime")).toBeNull();
  });
});