Three bugs preventing any SSE events from reaching clients:
1. SubscriptionRegistry::clone() deep-cloned the DashMaps instead of sharing
them. The sse_handler spawned a task with a disconnected clone, so
subscriptions.update() wrote into a throwaway copy — the fanout always saw
an empty registry and found zero connections to push to. Fixed by wrapping
both DashMaps in Arc so clone() is a cheap pointer copy sharing live state.
2. The SSE event data payload used .join("\ndata: ") to pre-embed the `data:`
prefix into the string, then handed it to axum's Event::data() which does
its own \n-splitting to add `data:` prefixes. This produced double-prefixed
lines (`data: data: elements ...`) that DataStar couldn't parse. Fixed by
using .join("\n") and letting axum format the data lines correctly.
3. The fanout skipped connections with None signals (new connections that had
not yet received a client action). This broke clock-style server-push events
on fresh connections. Fixed by falling back to "{}" instead of continue-ing.
https://claude.ai/code/session_0168cLRd1wr6LK9FjBsjA37W
Claude
0ab0f79749