diff --git a/packages/functions-compiler/README.md b/packages/functions-compiler/README.md
index 7c172d6d..efe77b0b 100644
--- a/packages/functions-compiler/README.md
+++ b/packages/functions-compiler/README.md
@@ -125,6 +125,12 @@ so a caller that needs a whole-app build must reject those itself.
 resolution the compiler itself performs. Install it in the worker or child
 process that runs a compile — not in a process that later needs the network.
 
+`@deno/loader` downloads dependencies through the global `fetch` and never
+retries, so the first compile in a process wraps `globalThis.fetch` once: GETs
+to those same dependency hosts are retried on a network error, 429 or 5xx, and
+each failure is logged as `base44.bundler.dependency_fetch_failed`. Every other
+request passes through untouched.
+
 ### Diagnostics
 
 The compiler ships no tracer and no service credentials. Hosts that want spans
diff --git a/packages/functions-compiler/src/dependency-fetch-retry.ts b/packages/functions-compiler/src/dependency-fetch-retry.ts
new file mode 100644
index 00000000..9a3c0248
--- /dev/null
+++ b/packages/functions-compiler/src/dependency-fetch-retry.ts
@@ -0,0 +1,76 @@
+/**
+ * Retries the dependency downloads `@deno/loader` makes through the global
+ * `fetch`. The loader never retries (its WASM HTTP client: "todo: implement
+ * retrying") and drops the failed download's error, so one registry blip deep
+ * in a large tree (Stagehand: ~350 downloads) fails the build as "Could not
+ * find constraint '<root package>' in the list of packages", or as a missing
+ * module when a tarball was lost.
+ *
+ * Only GETs to the dependency hosts are retried, on a network error, 429 or
+ * 5xx; a 404 is a real answer. Every other request — including the host's own
+ * API calls — passes straight through.
+ */
+
+import {
+  type FetchInput,
+  isDependencyHost,
+  requestUrl,
+} from "./fetch-guard.js";
+import { logEvent } from "./log.js";
+
+const RETRY_DELAYS_MS = [250, 1000];
+
+let installed = false;
+
+/** Wrap `globalThis.fetch` once, before the first loader is created. */
+export function installDependencyFetchRetry(): void {
+  if (installed) return;
+  installed = true;
+  globalThis.fetch = createRetryingFetch(globalThis.fetch.bind(globalThis));
+}
+
+export function createRetryingFetch(
+  originalFetch: typeof fetch,
+  delaysMs: readonly number[] = RETRY_DELAYS_MS,
+): typeof fetch {
+  return (async (input: FetchInput, init?: RequestInit) => {
+    const url = requestUrl(input);
+    const method =
+      init?.method ?? (input instanceof Request ? input.method : "GET");
+    if (method.toUpperCase() !== "GET" || !isDependencyHost(url.hostname)) {
+      return originalFetch(input, init);
+    }
+
+    for (let attempt = 0; ; attempt++) {
+      const delay = delaysMs[attempt];
+      let response: Response | undefined;
+      let error: unknown;
+      try {
+        response = await originalFetch(input, init);
+        if (response.status !== 429 && response.status < 500) return response;
+      } catch (err) {
+        error = err;
+      }
+      // The loader swallows this failure, so the log is the only place its
+      // real cause shows.
+      logEvent(
+        delay === undefined ? "error" : "warn",
+        "base44.bundler.dependency_fetch_failed",
+        {
+          url: url.href,
+          attempt: attempt + 1,
+          http_status: response?.status,
+          error: response
+            ? undefined
+            : String((error as Error)?.cause ?? error),
+        },
+      );
+      if (delay === undefined) {
+        if (response) return response;
+        throw error;
+      }
+      await response?.body?.cancel();
+      await new Promise((resolve) => setTimeout(resolve, delay));
+    }
+  }) as typeof fetch;
+}
diff --git a/packages/functions-compiler/src/esbuild/deno-resolver.ts b/packages/functions-compiler/src/esbuild/deno-resolver.ts
index 4807167f..1ba09360 100644
--- a/packages/functions-compiler/src/esbuild/deno-resolver.ts
+++ b/packages/functions-compiler/src/esbuild/deno-resolver.ts
@@ -36,6 +36,7 @@ import type {
   OnResolveResult,
   Plugin,
 } from "esbuild";
+import { installDependencyFetchRetry } from "../dependency-fetch-retry.js";
 import { lazyDenoLoader } from "../lazy-deps.js";
 import { logEvent } from "../log.js";
 import { USER_NAMESPACE } from "./user-files.js";
@@ -61,6 +62,7 @@ export function denoResolverPlugin(options: DenoResolverOptions = {}): Plugin {
   return {
     name: "deno-resolver",
     async setup(build) {
+      installDependencyFetchRetry();
       deno = await lazyDenoLoader();
       // Security: stop a dependency or data: module from reading host files.
       // Allow file: reads only from where deps live — the global cache, or this
diff --git a/packages/functions-compiler/src/fetch-guard.ts b/packages/functions-compiler/src/fetch-guard.ts
index aabfadb9..58cb17cc 100644
--- a/packages/functions-compiler/src/fetch-guard.ts
+++ b/packages/functions-compiler/src/fetch-guard.ts
@@ -46,7 +46,7 @@ export function createGuardedFetch(
   // `preconnect`), and the guard wraps only the call.
   return (async (input: FetchInput, init?: RequestInit) => {
     const url = requestUrl(input);
-    if (!isAllowedHost(url.hostname)) {
+    if (!isDependencyHost(url.hostname)) {
       logEvent("warn", "base44.bundler.fetch_blocked", { host: url.hostname });
       throw new Error(
         `Blocked fetch to disallowed host "${url.hostname}". Allowed: the npm and jsr registries and the esm.sh / deno.land CDNs — import dependencies via npm:, jsr:, or an https: URL on one of those hosts.`,
@@ -71,15 +71,15 @@ export function createGuardedFetch(
   }) as typeof fetch;
 }
 
-type FetchInput = Parameters<typeof fetch>[0];
+export type FetchInput = Parameters<typeof fetch>[0];
 
-function requestUrl(input: FetchInput): URL {
+export function requestUrl(input: FetchInput): URL {
   if (input instanceof URL) return input;
   if (typeof input === "string") return new URL(input);
   return new URL(input.url);
 }
 
-function isAllowedHost(hostname: string): boolean {
+export function isDependencyHost(hostname: string): boolean {
   return ALLOWED_HOST_SUFFIXES.some(
     (suffix) => hostname === suffix || hostname.endsWith(`.${suffix}`),
   );
diff --git a/packages/functions-compiler/test/dependency-fetch-retry.e2e.test.ts b/packages/functions-compiler/test/dependency-fetch-retry.e2e.test.ts
new file mode 100644
index 00000000..9373938d
--- /dev/null
+++ b/packages/functions-compiler/test/dependency-fetch-retry.e2e.test.ts
@@ -0,0 +1,55 @@
+/**
+ * One transient registry failure deep in a dependency tree must not fail the
+ * build. `@deno/loader` never retries, and reports the lost download as "Could
+ * not find constraint '<root package>' in the list of packages" — the Stagehand
+ * package-matrix row flaked on exactly that in CI.
+ */
+
+import { mkdtempSync, rmSync } from "node:fs";
+import { tmpdir } from "node:os";
+import path from "node:path";
+
+import { afterAll, beforeAll, expect, it } from "vitest";
+
+import { bundle } from "../src/bundler";
+
+// is-odd@3.0.1 depends on is-number; its metadata fails once.
+const FLAKY_URL = "https://registry.npmjs.org/is-number";
+
+let denoDir: string;
+let realFetch: typeof fetch;
+let flakyHits = 0;
+beforeAll(() => {
+  // A cold cache, so the loader really downloads is-number.
+  denoDir = mkdtempSync(path.join(tmpdir(), "bundler-retry-"));
+  process.env.DENO_DIR = denoDir;
+  // Replaced before the first bundle, as a host's fetch would be.
+  realFetch = globalThis.fetch;
+  globalThis.fetch = (async (
+    input: string | URL | Request,
+    init?: RequestInit,
+  ) => {
+    if (String(input) === FLAKY_URL && flakyHits++ === 0) {
+      return new Response("upstream unavailable", { status: 503 });
+    }
+    return realFetch(input, init);
+  }) as typeof fetch;
+});
+afterAll(() => {
+  globalThis.fetch = realFetch;
+  delete process.env.DENO_DIR;
+  rmSync(denoDir, { recursive: true, force: true });
+});
+
+it("retries a dependency download that failed transiently", async () => {
+  const result = await bundle({
+    entry: "main.ts",
+    files: {
+      "main.ts": `import isOdd from "npm:is-odd@3.0.1";
+Deno.serve(() => new Response(String(isOdd(3))));`,
+    },
+  });
+
+  expect(result.ok ? [] : result.errors).toEqual([]);
+  expect(flakyHits).toBe(2);
+});
diff --git a/packages/functions-compiler/test/dependency-fetch-retry.test.ts b/packages/functions-compiler/test/dependency-fetch-retry.test.ts
new file mode 100644
index 00000000..ff17e1a3
--- /dev/null
+++ b/packages/functions-compiler/test/dependency-fetch-retry.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it, vi } from "vitest";
+
+import { createRetryingFetch } from "../src/dependency-fetch-retry";
+
+const PACKUMENT = "https://registry.npmjs.org/zod";
+
+const retryingOver = (original: () => Promise<Response>) =>
+  createRetryingFetch(original as unknown as typeof fetch, [0, 0]);
+
+describe("dependency fetch retry", () => {
+  it("retries network errors and 5xx, then gives up with the last answer", async () => {
+    const original = vi
+      .fn()
+      .mockRejectedValueOnce(new TypeError("fetch failed"))
+      .mockResolvedValue(new Response("", { status: 503 }));
+
+    const res = await retryingOver(original)(PACKUMENT);
+
+    expect(res.status).toBe(503);
+    expect(original).toHaveBeenCalledTimes(3);
+  });
+
+  it("leaves a 404 and the host's own requests alone", async () => {
+    const unavailable = vi.fn(async () => new Response("", { status: 503 }));
+    await retryingOver(unavailable)("https://app.base44.com/api/apps");
+    await retryingOver(unavailable)(PACKUMENT, { method: "POST" });
+    expect(unavailable).toHaveBeenCalledTimes(2);
+
+    const missing = vi.fn(async () => new Response("", { status: 404 }));
+    await retryingOver(missing)(PACKUMENT);
+    expect(missing).toHaveBeenCalledTimes(1);
+  });
+});