fix(csp): handle base64-encoded Clerk publishable keys

Investigation with the running container revealed the previous fix
was correct on the deployed server but didn't help the user because
NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY in their .env has the placeholder
'pk_test_...' from .env.example, not the readable form like
'pk_test_useful-louse-74-O42m8W' I tested against. The actual key is
in Clerk's older "encoded" format:

  pk_test_dXNlZnVsLWxvdXNlLTc0LmNsZXJrLmFjY291bnRzLmRldiQ

The base64 portion decodes to the literal FAPI host
'useful-louse-74.clerk.accounts.dev' (with a trailing '$' separator),
which is exactly the host shown in the error message. So script-src
needs to allow exactly that host, and my previous regex only knew
the readable form.

clerkFrontendApiHost() now handles both formats:

  Form 1 (encoded): pk_test_<base64slug>\$
                    /-> decode b64 /-> <slug>.clerk.accounts.dev
                                   (or .clerk.services for ?)
                    Note: the encoded payload always carries the
                    literal hostname regardless of test/live; we
                    accept either well-known TLD suffix on the
                    decoded string.

  Form 2 (readable): pk_test_<slug>-<randomSuffix>
                    /-> <slug>.clerk.accounts.dev
                    Captured greedily (slug may contain digits and
                    hyphens) — kept as a fallback.

Defensive fall-throughs ensure a string that decodes to garbage
(e.g. a readable-form key passed through the b64 regex) doesn't
silently return null — it falls through to form 2.

Verified against four cases:
  pk_test_dXNlZnVsLWxvdXNlLTc0...     -> useful-louse-74.clerk.accounts.dev ✓
  pk_test_useful-louse-74-O42m8W      -> useful-louse-74.clerk.accounts.dev ✓
  pk_live_dXNlZnVsLWxvdXNlLTc0...     -> useful-louse-74.clerk.accounts.dev ✓
  pk_test_invalid-garbage             -> invalid.clerk.accounts.dev (form 2)

The user must rebuild and redeploy for the new CSP header to take
effect — the previously-served header is cached in the running
container's standalone bundle and won't refresh until container
restart with the new build.

next.config.ts

@@ -5,15 +5,43 @@ const s3Host = process.env.S3_ENDPOINT
   : "";
 
 // Derive the Clerk frontend API host from the publishable key so the
-// CSP allowlist always matches the active environment.
+// CSP allowlist always matches the active environment. Clerk supports
-// Clerk key format is:
+// two publishable key formats:
-//   pk_test_<slug>-<randomSuffix>  -> <slug>.clerk.accounts.dev
+//
-//   pk_live_<slug>-<randomSuffix>  -> <slug>.clerk.services
+//   1) "Encoded" form (older):  pk_test_<base64slug>$
-// The slug itself may contain hyphens and digits, so the suffix is
+//      The base64 portion decodes to "<slug>.clerk.accounts.dev" (test)
-// only the final dash-group. The regex greedily captures the slug.
+//      or "<slug>.clerk.services" (live). Trailing '$' is a separator.
+//
+//   2) "Readable" form (newer): pk_test_<slug>-<randomSuffix>
+//      -> <slug>.clerk.accounts.dev (test) or <slug>.clerk.services.
+//      The slug may itself contain hyphens and digits, so only the
+//      final dash-group is captured as the suffix.
 function clerkFrontendApiHost(): string | null {
   const key = process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY;
   if (!key) return null;
+
+  // Form 1: base64-encoded FAPI URL. Match everything between the
+  // 'pk_test_'/'pk_live_' prefix and an optional trailing '$'.
+  const enc = key.match(/^pk_(test|live)_([A-Za-z0-9+/=_-]+)\$?$/);
+  if (enc) {
+    const b64 = enc[2].replace(/-/g, "+").replace(/_/g, "/");
+    if (/^[A-Za-z0-9+/=]+$/.test(b64)) {
+      try {
+        const padded = b64 + "=".repeat((4 - (b64.length % 4)) % 4);
+        const decoded = Buffer.from(padded, "base64").toString("utf8");
+        // If the decoded string doesn't look like a Clerk FAPI host
+        // (e.g. it's garbage from decoding a non-base64 readable-form
+        // key), fall through to form 2 rather than returning null.
+        const fapi = decodeFapiHost(decoded);
+        if (fapi) return fapi;
+      } catch {
+        // fall through to form 2
+      }
+    }
+    // fall through to form 2 if the slug is non-base64 (e.g. readable form)
+  }
+
+  // Form 2: readable slug + random suffix.
   const m = key.match(/^pk_(test|live)_(.+?)-([a-z0-9]+)$/i);
   if (!m) return null;
   const slug = m[2].toLowerCase();
@@ -22,6 +50,20 @@ function clerkFrontendApiHost(): string | null {
     : `${slug}.clerk.services`;
 }
 
+function decodeFapiHost(decoded: string): string | null {
+  // The decoded string is the FAPI host (e.g.
+  // 'useful-louse-74.clerk.accounts.dev$'). Note: the encoded base64
+  // payload always carries the literal FAPI host regardless of test vs
+  // live mode — both `pk_test_...` and `pk_live_...` can decode to an
+  // '.accounts.dev' host when the deployment is on the test endpoint.
+  // We accept either well-known Clerk FAPI host pattern.
+  const host = decoded.trim().replace(/\$$/, "").trim().toLowerCase();
+  if (host.endsWith(".clerk.accounts.dev") || host.endsWith(".clerk.services")) {
+    return host;
+  }
+  return null;
+}
+
 const clerkFapiHost = clerkFrontendApiHost();
 
 const csp = [