test(imaging): retry transient edge failures instead of flaking the suite

The cross-browser imaging job runs against the public origin, so every request
goes through Cloudflare. One chromium run of "rejects malformed figures ›
missing figure" came back 525 (Cloudflare: TLS handshake to the origin failed)
after a 40s stall — the request never reached the CMS, so a 400 was impossible
to observe and the assertion was effectively testing the network. It passed on
both firefox and webkit, which is the signature of an edge hiccup rather than a
regression.

`e2e/imaging/imaging-target.ts` now owns `getThroughEdge` / `fetchThroughEdge`,
which retry on the statuses that mean "the app was never reached"
(502/503/504 plus Cloudflare's 520-527) with a short backoff, and both
edge-fronted specs use them. A genuinely broken edge still exhausts the retries
and fails the run, so nothing is masked.

Verified: 84 passed / 21 skipped / 0 failed against epicnabbo.nl with
IMAGING_EDGE=1 across chromium, firefox and webkit.

e2e/imaging/imaging-target.ts

@@ -1,3 +1,5 @@
+import type { APIRequestContext, APIResponse } from "@playwright/test";
+
 /**
  * Where the imaging specs are pointed.
  *
@@ -12,6 +14,56 @@
  */
 export const IS_EDGE = process.env.IMAGING_EDGE === "1";
 
+/**
+ * Failures that mean "the request never reached the app".
+ *
+ * Cloudflare answers the 520-527 family when its own handshake to the origin
+ * fails, and gateways add 502/503/504. Retrying those is not papering over a
+ * bug: the assertion under test is about the CMS, and a 525 says nothing about
+ * it. A genuinely broken edge still exhausts the retries and fails the test.
+ */
+const TRANSIENT_EDGE_STATUSES = new Set([
+	502, 503, 504, 520, 521, 522, 523, 524, 525, 526, 527,
+]);
+const EDGE_RETRY_ATTEMPTS = 3;
+const EDGE_RETRY_DELAY_MS = 500;
+
+async function withEdgeRetry(
+	send: () => Promise<APIResponse>,
+): Promise<APIResponse> {
+	let response = await send();
+	for (
+		let attempt = 1;
+		attempt < EDGE_RETRY_ATTEMPTS &&
+		TRANSIENT_EDGE_STATUSES.has(response.status());
+		attempt += 1
+	) {
+		await new Promise((resolve) =>
+			setTimeout(resolve, EDGE_RETRY_DELAY_MS * attempt),
+		);
+		response = await send();
+	}
+	return response;
+}
+
+/** GET that survives a transient edge/transport failure. */
+export function getThroughEdge(
+	request: APIRequestContext,
+	url: string,
+	options: Parameters<APIRequestContext["get"]>[1] = {},
+): Promise<APIResponse> {
+	return withEdgeRetry(() => request.get(url, options));
+}
+
+/** POST/OPTIONS/… counterpart of `getThroughEdge`. */
+export function fetchThroughEdge(
+	request: APIRequestContext,
+	url: string,
+	options: Parameters<APIRequestContext["fetch"]>[1] = {},
+): Promise<APIResponse> {
+	return withEdgeRetry(() => request.fetch(url, options));
+}
+
 // The exact figure that regressed in production: the game client appends a
 // trailing `.<n>` segment that the renderer ignores, but the previous
 // validation regex rejected with a 400.