Switch default signaling to reachable public relays

[lsegal]

Root cause

Write's default signaling relay, wss://y-webrtc-eu.fly.dev, is offline (hostname resolves, connections time out). The hosted embed on write.subscript.to sets no signaling-url, so browsers opening a Share Draft link never find each other.

Change

Per the instruction on #7 ("find another public signaling server"), I probed public y-webrtc relays with a live two-client subscribe/publish relay test (2026-10-03):

Relay	Result
wss://y-webrtc-signaling.fly.dev	✅ relays messages
wss://y-webrtc.fly.dev	✅ relays messages
wss://y-webrtc-eu.fly.dev (old default)	❌ connect error
wss://signaling.yjs.dev, y-webrtc-signaling-{eu,us}.herokuapp.com, y-webrtc-signaling-{eu,us}.fly.dev, y-webrtc-us.fly.dev	❌ connect error

• app/src/lib/config.ts: default signalingUrl is now wss://y-webrtc-signaling.fly.dev,wss://y-webrtc.fly.dev. Write already accepts a comma-separated list and y-webrtc connects to every relay concurrently, so either one being down doesn't break sharing.
• Extracted the existing comma-splitting into an exported signalingUrls() helper so it can be tested.
• app/.env.example, signaling/README.md, and the root README no longer describe wss://y-webrtc-eu.fly.dev; they document the new defaults (the root README's config table previously listed the wrong default too). signaling/README.md now notes these are community relays with no uptime guarantee.

User impact

Share Draft links connect peers again without any self-hosted signaling. The hosted write.subscript.to page picks this up once it's rebuilt with this version of the embed bundle (it currently bakes in the old default).

Tests

• New app/src/lib/config.test.ts: default relays, old relay absent, comma-separated override parsing.
• pnpm run lint and pnpm run test (16 files, 47 tests) pass locally.
• End-to-end: ran pnpm dev with no .env.local (so only the new defaults), opened /#room=<random> in two isolated headless Chrome contexts. Both showed 2 in room, and edits synced A→B and B→A.

Changelog

No changelog entry: the project has no changelog.

Screenshots

Not applicable: no UI code changed.

Closes #7

Agents: claude-code (claude-opus-5-5)

[lsegal]

Merged. The new default relays are verified locally (two isolated Chrome contexts showed 2 in room and synced edits both ways), but write.subscript.to serves a prebuilt embed bundle that still has wss://y-webrtc-eu.fly.dev baked in. CI can't cover the remaining checks.

Manual verification

• Rebuild and redeploy the hosted embed on write.subscript.to from main (pnpm build:embed, then publish the bundle). Alternatively, set signaling-url="wss://y-webrtc-signaling.fly.dev,wss://y-webrtc.fly.dev" on the hosted <subscript-write> element.
• Check that the served /assets/subscript-write-*.js no longer contains y-webrtc-eu.fly.dev.
• Open the same Share Draft link in two browsers on write.subscript.to. Both should show "2 in room" and sync edits both ways.
• Optional, for long-term reliability: the new defaults are community-run relays with no uptime guarantee. Deploying signaling/ (pnpm deploy:signaling) on the account that serves write.subscript.to and setting the hosted signaling-url to it would remove that dependency.