fix(avatar): retry blob fetch with backoff to handle CDN propagation

[Copilot]

onUploadCompleted fetches the uploaded blob via its CDN URL to convert it to WebP, but in production the CDN hasn't propagated the file yet, returning a 404. Preview deployments don't exhibit this due to different CDN caching behavior.

• New lib/utils/fetch-with-retry.ts: Retries fetch with exponential backoff (1s → 2s → 4s, 3 retries max)
• app/api/avatar/upload/route.ts: fetch(blob.url) → fetchWithRetry(blob.url)

// Before: immediate fetch fails if CDN hasn't propagated
const response = await fetch(blob.url);

// After: retries with exponential backoff
const response = await fetchWithRetry(blob.url);

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
rxlab-auth	Ready	Preview, Comment	Mar 8, 2026 0:13am

[Copilot]

Pull request overview

This PR addresses intermittent production 404s during avatar processing by adding a retrying fetch helper with exponential backoff, and using it when re-fetching the newly uploaded blob for WebP conversion.

Changes:

• Added fetchWithRetry utility to retry fetch() with exponential backoff.
• Added unit tests for fetchWithRetry using bun:test.
• Updated avatar upload onUploadCompleted to use fetchWithRetry(blob.url) instead of a single fetch(blob.url).

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
lib/utils/fetch-with-retry.ts	Introduces a reusable fetch-with-retries helper used to mitigate CDN propagation delays.
lib/utils/fetch-with-retry.test.ts	Adds unit tests covering success, retry, and exhaustion paths.
app/api/avatar/upload/route.ts	Switches blob download to the retrying fetch helper in onUploadCompleted.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

fetchWithRetry retries on any non-2xx response and does not retry when fetch() throws (e.g., transient network/DNS errors). Since this helper is intended for CDN propagation (typically 404) it should either accept a retry predicate or restrict retries to expected retriable cases (e.g., 404/5xx), and treat thrown fetch errors as retryable too.

Suggested change

	export async function fetchWithRetry(
	url: string,
	maxRetries: number = 3,
	baseDelayMs: number = 1000
	): Promise<Response> {
	let lastResponse: Response = await fetch(url);
	for (let attempt = 1; attempt <= maxRetries; attempt++) {
	if (lastResponse.ok) {
	return lastResponse;
	}
	const delay = baseDelayMs * Math.pow(2, attempt - 1);
	await new Promise((resolve) => setTimeout(resolve, delay));
	lastResponse = await fetch(url);
	}
	return lastResponse;
	/**
	* Decide whether a given HTTP status code should be retried.
	* For CDN propagation we primarily expect 404s until the asset is available,
	* and 5xx responses may also be transient.
	*/
	function shouldRetryStatus(status: number): boolean {
	return status === 404 || status >= 500;
	}
	export async function fetchWithRetry(
	url: string,
	maxRetries: number = 3,
	baseDelayMs: number = 1000
	): Promise<Response> {
	let lastResponse: Response | null = null;
	let lastError: unknown | null = null;
	const attemptFetch = async () => {
	try {
	lastResponse = await fetch(url);
	lastError = null;
	} catch (err) {
	lastResponse = null;
	lastError = err;
	}
	};
	// Initial attempt before applying any delay.
	await attemptFetch();
	for (let attempt = 1; attempt <= maxRetries; attempt++) {
	if (lastResponse) {
	if (lastResponse.ok) {
	return lastResponse;
	}
	// If the status is not considered retriable, stop retrying.
	if (!shouldRetryStatus(lastResponse.status)) {
	return lastResponse;
	}
	} else if (lastError && attempt > maxRetries) {
	// No response and we've exhausted retries: rethrow the last error.
	throw lastError;
	}
	const delay = baseDelayMs * Math.pow(2, attempt - 1);
	await new Promise((resolve) => setTimeout(resolve, delay));
	await attemptFetch();
	}
	// After all retries, return the last response if we have one,
	// otherwise rethrow the last encountered error.
	if (lastResponse) {
	return lastResponse;
	}
	if (lastError) {
	throw lastError;
	}
	// Fallback: this should be unreachable, but keep type-safety.
	throw new Error("fetchWithRetry failed without a response or error");

[Copilot]

On failed attempts, the previous Response body is discarded without being consumed/cancelled before the next fetch(). In Node/undici this can keep connections open and lead to resource/socket exhaustion under load. Cancel or drain lastResponse.body before sleeping/retrying (ideally in a try/finally).