diff --git a/src/lib/microcosm/spacedust.ts b/src/lib/microcosm/spacedust.ts
--- a/src/lib/microcosm/spacedust.ts
+++ b/src/lib/microcosm/spacedust.ts
@@ -6,7 +6,7 @@
  *
  * @see spacedust.json at the repo root
  */
-import {MICROCOSM_USER_AGENT, SPACEDUST_URL} from '#/env'
+import {SPACEDUST_URL} from '#/env'
 
 export type SpacedustSubscription = {
   /** Link sources to receive, e.g. `app.bsky.feed.like:subject.uri`. */
@@ -75,17 +75,16 @@
 /**
  * Open a Spacedust subscription. Returns a handle with `.close()`.
  *
- * Note: `User-Agent` can't be set on a browser WebSocket; it's encoded into the
- * protocol field where supported so microcosm can still attribute the client.
+ * Note: do NOT request a WebSocket subprotocol. Spacedust doesn't negotiate one,
+ * and if the client asks for a subprotocol the server doesn't echo back, the
+ * handshake fails ("Server sent no subprotocol"). `User-Agent` can't be set on a
+ * browser WebSocket, so the client is simply not attributed here.
  */
 export function subscribe(
   sub: SpacedustSubscription,
   handlers: SpacedustHandlers,
 ): {close: () => void} {
-  const ws = new WebSocket(buildUrl(sub), [
-    // best-effort attribution; ignored by servers that don't negotiate it
-    MICROCOSM_USER_AGENT.replace(/[^\w.-]/g, '_'),
-  ])
+  const ws = new WebSocket(buildUrl(sub))
 
   ws.onopen = () => handlers.onOpen?.()
   ws.onerror = e => handlers.onError?.(e)