@@ -170,6 +170,23 @@ export function isExpiredTokenError(error: unknown): boolean {
   return false;
 }
 
+/**
+ * True when `fetch` gave up waiting for response headers (undici's
+ * `HeadersTimeoutError`, 300 seconds by default). The request reached the
+ * server, which is still working on it.
+ */
+export function isHeadersTimeoutError(error: unknown): boolean {
+  let current = error;
+  for (let depth = 0; depth < 6 && current !== null && typeof current === 'object'; depth++) {
+    const { code, name } = current as { code?: unknown; name?: unknown };
+    if (code === 'UND_ERR_HEADERS_TIMEOUT' || name === 'HeadersTimeoutError') {
+      return true;
+    }
+    current = (current as { cause?: unknown }).cause;
+  }
+  return false;
+}
+
 function isPreflightRejection(error: unknown): boolean {
   return (
     error instanceof PlatformApiError &&
@@ -577,6 +594,10 @@ export type ManifestOnlyDeployPayload = DeployUploadPayload;
  * - Only `fetch` rejections (`TypeError` — no HTTP response) are retried.
  *   A Response of any status means the server answered; surface it
  *   verbatim rather than replay a request it may have accepted.
+ * - A headers timeout is retried too. Every attempt sends the same
+ *   idempotency key, so once an earlier request has created its deployment,
+ *   a receipt-aware platform answers the retry with that deployment's
+ *   receipt and the CLI follows it to the real result.
  * - A rejected fetch does NOT prove the request never arrived — the
  *   connection may have dropped after delivery. Arbitration is left to
  *   the server's precheck, the only atomic (project-locked) verdict: if
@@ -590,6 +611,11 @@ export type ManifestOnlyDeployPayload = DeployUploadPayload;
  */
 const DEPLOY_POST_MAX_RETRIES = 3;
 const DEPLOY_POST_BACKOFF_MS = [1000, 5000, 10000];
+/**
+ * Every transport failure is retried, so a `TypeError` thrown by the deploy
+ * POST always comes after this many attempts.
+ */
+export const DEPLOY_POST_ATTEMPTS: number = DEPLOY_POST_MAX_RETRIES + 1;
 const DEPLOY_OBSERVATION_TIMEOUT_MS = 30_000;
 const DEPLOY_OBSERVATION_DEADLINE_MS = 30 * 60_000;
 const DEPLOY_OBSERVATION_BACKOFF_MS = [1000, 2000, 5000, 10_000, 30_000];
 
@@ -1,4 +1,10 @@
-import { isCliOutdatedError, parsePlatformErrorBody, PlatformApiError } from './client.ts';
+import {
+  DEPLOY_POST_ATTEMPTS,
+  isCliOutdatedError,
+  isHeadersTimeoutError,
+  parsePlatformErrorBody,
+  PlatformApiError,
+} from './client.ts';
 import { platformErrorMessage } from './platform-errors.ts';
 
 const BODY_SNIPPET_MAX = 200;
@@ -27,6 +33,31 @@ function appendTrailingLines(
   return appendLogLine(appendDeploymentLine(message, deploymentId), logPath);
 }
 
+/**
+ * Describe the deepest `cause` of an error in one short line, e.g.
+ * `getaddrinfo ENOTFOUND api.example.com` under `fetch failed`.
+ */
+function describeRootCause(err: Error): string | null {
+  let root: unknown = err;
+  for (let depth = 0; depth < 6; depth++) {
+    const cause = (root as { cause?: unknown }).cause;
+    if (cause === null || typeof cause !== 'object') {
+      break;
+    }
+    root = cause;
+  }
+  if (root === err) {
+    return null;
+  }
+  const { code, message } = root as { code?: unknown; message?: unknown };
+  const text = typeof message === 'string' ? message.trim() : '';
+  const codeText = typeof code === 'string' ? code : '';
+  if (!text) {
+    return codeText || null;
+  }
+  return codeText && !text.includes(codeText) ? `${codeText}: ${text}` : text;
+}
+
 /**
  * Format a server-emitted `event: 'error'` payload with an optional deployment id.
  */
@@ -56,14 +87,18 @@ export function formatConnectionLostMessage(
  * Convert an exception thrown during the deploy NDJSON stream into a
  * user-facing `Error` with a readable message.
  *
- * Three cases:
+ * Four cases:
  *   1. `PlatformApiError` with 409 + a JSON body carrying `{error, deployment}`
  *      — surface the server-supplied error and prefer the body's deployment id.
  *   2. Any other `PlatformApiError` — retain the client's actionable message and
  *      structured error fields; opaque provider failures use a trimmed body snippet.
- *   3. Anything else — preserve the original message under a `Connection lost
- *      during deploy: <original>` prefix so the caller can still tell network,
- *      parse, and transport errors apart.
+ *   3. A headers timeout on the last deploy POST attempt — the platform sent
+ *      no response in time. Explain that the deploy may still finish and how
+ *      to check and retry.
+ *   4. Anything else — preserve the original message, plus its root cause when
+ *      there is one, under a `Connection lost during deploy: <original>`
+ *      prefix so the caller can still tell network, parse, and transport
+ *      errors apart.
  */
 export function formatStreamDeployError(
   err: unknown,
@@ -98,10 +133,23 @@ export function formatStreamDeployError(
     return err;
   }
 
+  if (isHeadersTimeoutError(err)) {
+    const lines = [
+      `deploy: The Void platform did not respond while preparing the deploy. Tried ${DEPLOY_POST_ATTEMPTS} times; the last try waited 5 minutes.`,
+      'It may still finish. Check `void project status`, then run `void deploy` again to retry.',
+    ];
+    if (logPath) {
+      lines.push('If this keeps happening, share the detailed log below.');
+    }
+    return new Error(appendTrailingLines(lines.join('\n'), deploymentId, logPath));
+  }
+
   const original = err instanceof Error ? err.message : String(err);
+  const rootCause = err instanceof Error ? describeRootCause(err) : null;
+  const detail = rootCause && rootCause !== original ? ` (${rootCause})` : '';
   return new Error(
     appendTrailingLines(
-      `deploy: Connection lost during deploy: '${original}'.`,
+      `deploy: Connection lost during deploy: '${original}'${detail}.`,
       deploymentId,
       logPath,
     ),
 
@@ -1,5 +1,9 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from 'vite-plus/test';
-import { PlatformClient, type ManifestOnlyDeployPayload } from '../../src/cli/client.ts';
+import {
+  DEPLOY_POST_ATTEMPTS,
+  PlatformClient,
+  type ManifestOnlyDeployPayload,
+} from '../../src/cli/client.ts';
 import type { DeployManifest } from '../../src/cli/types.ts';
 import { withPlatformDiscovery } from '../helpers/platform-discovery.ts';
 
@@ -296,7 +300,9 @@ describe('PlatformClient.finalizeDeploy', () => {
       posts++;
       if (posts === 1) {
         return Promise.reject(
-          new TypeError('fetch failed', { cause: new Error('read ECONNRESET') }),
+          new TypeError('fetch failed', {
+            cause: Object.assign(new Error('read ECONNRESET'), { code: 'ECONNRESET' }),
+          }),
         );
       }
       return Promise.resolve(
@@ -450,6 +456,85 @@ describe('PlatformClient.finalizeDeploy', () => {
     expect(fetchMock).toHaveBeenCalledTimes(1);
   });
 
+  function headersTimeoutError() {
+    const cause = Object.assign(new Error('Headers Timeout Error'), {
+      name: 'HeadersTimeoutError',
+      code: 'UND_ERR_HEADERS_TIMEOUT',
+    });
+    return { cause, error: new TypeError('fetch failed', { cause }) };
+  }
+
+  const idempotencyKeys = () =>
+    deployPostCalls().map(
+      ([, init]) => (init.headers as Record<string, string>)['x-void-deploy-idempotency-key'],
+    );
+
+  it('retries a headers timeout with the same idempotency key, then rethrows it', async () => {
+    const { cause, error } = headersTimeoutError();
+    fetchMock.mockRejectedValue(error);
+
+    vi.useFakeTimers();
+    const cliLog = makeCliLog();
+    const client = new PlatformClient(token, { apiUrl, cliLog });
+    try {
+      const assertion = expect(
+        client.finalizeDeploy(projectId, makePayload()).next(),
+      ).rejects.toMatchObject({ message: 'fetch failed', cause });
+      await vi.runAllTimersAsync();
+      await assertion;
+
+      expect(deployPostCalls()).toHaveLength(4);
+      expect(DEPLOY_POST_ATTEMPTS).toBe(4);
+      expect(new Set(idempotencyKeys()).size).toBe(1);
+      const retries = cliLog.warn.mock.calls.filter(([msg]) => msg === 'deploy_fetch_retry');
+      expect(retries.map(([, fields]) => fields?.delayMs)).toEqual([1000, 5000, 10000]);
+      expect(cliLog.error).toHaveBeenCalledWith(
+        'deploy_fetch_rejected',
+        expect.any(TypeError),
+        expect.objectContaining({ attempts: 4 }),
+      );
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
+  it('follows the existing deployment receipt returned to a retry after a headers timeout', async () => {
+    const done = {
+      event: 'done',
+      deployment: 'dpl_existing',
+      url: 'https://x.void.app',
+      urls: [],
+      assets: 1,
+      workers: 1,
+      seq: 3,
+    };
+    fetchMock
+      .mockRejectedValueOnce(headersTimeoutError().error)
+      .mockResolvedValueOnce(
+        ndjsonStreamResponse([
+          { event: 'start', deploymentId: 'dpl_existing', seq: 1 },
+          { event: 'worker_upload', seq: 2 },
+          done,
+        ]),
+      );
+
+    vi.useFakeTimers();
+    try {
+      const deploy = collectDeploy();
+      await vi.runAllTimersAsync();
+      expect(await deploy).toEqual([
+        { event: 'start', deploymentId: 'dpl_existing' },
+        { event: 'worker_upload', seq: 2 },
+        done,
+      ]);
+      expect(deployPostCalls()).toHaveLength(2);
+      const [first, second] = idempotencyKeys();
+      expect(second).toBe(first);
+    } finally {
+      vi.useRealTimers();
+    }
+  });
+
   it('does not retry HTTP error responses — the server answered', async () => {
     fetchMock.mockResolvedValue(new Response('busted', { status: 503 }));
     const client = makeClient();
 
@@ -63,6 +63,71 @@ describe('formatStreamDeployError', () => {
     expect(formatted.message).toContain('fetch failed');
   });
 
+  it('explains a headers timeout after the last retry in plain words and keeps the log line', () => {
+    const err = new TypeError('fetch failed', {
+      cause: Object.assign(new Error('Headers Timeout Error'), {
+        name: 'HeadersTimeoutError',
+        code: 'UND_ERR_HEADERS_TIMEOUT',
+      }),
+    });
+
+    const formatted = formatStreamDeployError(err, null, '/tmp/deploy.jsonl');
+
+    expect(formatted.message).toBe(
+      [
+        'deploy: The Void platform did not respond while preparing the deploy. Tried 4 times; the last try waited 5 minutes.',
+        'It may still finish. Check `void project status`, then run `void deploy` again to retry.',
+        'If this keeps happening, share the detailed log below.',
+        'Detailed log: /tmp/deploy.jsonl',
+      ].join('\n'),
+    );
+  });
+
+  it('omits the log hint for a headers timeout when no log was written', () => {
+    const err = new TypeError('fetch failed', {
+      cause: Object.assign(new Error('Headers Timeout Error'), {
+        code: 'UND_ERR_HEADERS_TIMEOUT',
+      }),
+    });
+
+    const formatted = formatStreamDeployError(err, null, null);
+
+    expect(formatted.message).not.toContain('log');
+    expect(formatted.message).toContain('void project status');
+  });
+
+  it('adds the root cause of a fetch failure', () => {
+    const err = new TypeError('fetch failed', {
+      cause: Object.assign(new Error('getaddrinfo ENOTFOUND api.example.com'), {
+        code: 'ENOTFOUND',
+      }),
+    });
+
+    const formatted = formatStreamDeployError(err, null, '/tmp/deploy.jsonl');
+
+    expect(formatted.message).toBe(
+      "deploy: Connection lost during deploy: 'fetch failed' (getaddrinfo ENOTFOUND api.example.com).\n" +
+        'Detailed log: /tmp/deploy.jsonl',
+    );
+  });
+
+  it('uses the cause code when the root cause has no message', () => {
+    const refused = Object.assign(new AggregateError([], ''), { code: 'ECONNREFUSED' });
+    const closed = Object.assign(new Error('other side closed'), {
+      name: 'SocketError',
+      code: 'UND_ERR_SOCKET',
+    });
+
+    expect(
+      formatStreamDeployError(new TypeError('fetch failed', { cause: refused }), null).message,
+    ).toBe("deploy: Connection lost during deploy: 'fetch failed' (ECONNREFUSED).");
+    expect(
+      formatStreamDeployError(new TypeError('fetch failed', { cause: closed }), null).message,
+    ).toBe(
+      "deploy: Connection lost during deploy: 'fetch failed' (UND_ERR_SOCKET: other side closed).",
+    );
+  });
+
   it('includes the deployment id for generic mid-stream errors when known', () => {
     const err = new Error('reader canceled');
 
 
@@ -1,5 +1,6 @@
 import { and, eq, getTableColumns, lte, ne, or, sql } from 'drizzle-orm';
 import { paginatedR2Delete } from './assets.ts';
+import { R2_CONCURRENCY } from './concurrency.ts';
 import { createDb, type Db, type DbOrTx } from './db.ts';
 import type { DeploymentInput, DeploymentOperation } from './deployment-operation-types.ts';
 import type { ApiEnv } from './env.ts';
@@ -109,14 +110,43 @@ export async function prepareDeploymentInput(
   };
   delete input.body.workerFiles;
   try {
+    // Hash one module at a time so at most one extra copy of module bytes is
+    // alive beside the decoded Blobs; a near-cap request already sits close
+    // to the isolate memory limit.
+    const modules: DeploymentInput['modules'] = [];
     for (let index = 0; index < files.length; index++) {
       const { name, content } = files[index]!;
-      const bytes = await content.arrayBuffer();
-      const digest = await sha256Hex(bytes);
-      const key = `${prefix}${index}`;
-      await r2.put(key, bytes);
-      input.modules.push({ name, key, digest, type: content.type });
+      const digest = await sha256Hex(await content.arrayBuffer());
+      modules.push({ name, key: `${prefix}${index}`, digest, type: content.type });
     }
+    // The request has not answered yet, so upload the Blobs themselves in
+    // parallel. Workers let at most six R2 calls wait for a response at once
+    // (R2_CONCURRENCY); a larger pool would only queue inside the runtime.
+    // After the first failure no new put starts, and every started put
+    // settles before cleanup so none lands under the prefix after it was
+    // deleted.
+    let next = 0;
+    let failed = false;
+    const workers = await Promise.allSettled(
+      Array.from({ length: Math.min(R2_CONCURRENCY, files.length) }, async () => {
+        while (!failed && next < files.length) {
+          const index = next++;
+          try {
+            await r2.put(modules[index]!.key, files[index]!.content);
+          } catch (error) {
+            failed = true;
+            throw error;
+          }
+        }
+      }),
+    );
+    const rejected = workers.find(
+      (result): result is PromiseRejectedResult => result.status === 'rejected',
+    );
+    if (rejected) {
+      throw rejected.reason;
+    }
+    input.modules = modules;
     const identity = JSON.stringify({
       body: input.body,
       modules: input.modules.map(({ name, digest, type }) => ({ name, digest, type })),