fix(collab): stop content duplication + fix false unreachable probe

[thetechjon]

Two runtime bugs in the live-collaboration feature, exposed now that beta sets NEXT_PUBLIC_YJS_WS_URL.

BUG 1 — false "Live: unreachable" pill (src/hooks/useCollaboration.ts)

Root cause. The Phase-A connectivity probe opened new WebSocket(url) against the bare configured URL (wss://<host>/<token>, no room). The Cloudflare worker (collab-server/src/index.ts) reads the last path segment as the room and the second-to-last as the auth token. A single-segment path therefore has no token -> the worker returns 403 -> the probe reported the server unreachable, even though the real document binding (which dials <url>/<room> via WebsocketProvider) authenticates fine.

Fix. The probe now dials a dedicated __probe__ room (buildProbeUrl), so it hits the /<token>/<room> shape the worker requires and the socket is accepted. The worker's auth-token check is untouched. The pill's exposed url stays the bare configured value (used in the tooltip).

BUG 2 — content DUPLICATION / data integrity (src/components/editor/CodeMirrorEditor.tsx)

Root cause. The CodeMirror editor was created with value={initialContent} and the collab binding seeded the same note body into the Y.Text. yCollab's ySync plugin only registers an observer on construction — it never reconciles the editor's existing doc against the (empty) Y.Text. So when the seed-on-empty inserted the body into Y.Text after the first sync, the observer replayed that insert on top of the body already in the editor -> the body rendered twice, and the doubled text was what got saved back to the note (and would sync to GitHub = corruption).

Fix. When collab is enabled (getConfiguredUrl() != null — the exact gate the collab effect uses), the editor is built empty and the Y.Text becomes the single source of content. The seeder sees its body exactly once; a joiner (empty local note) receives the shared body over the wire exactly once and never re-seeds. With collab off (NEXT_PUBLIC_YJS_WS_URL unset) the editor is byte-for-byte unchanged. The seed-on-empty logic in collabExtension.ts was already correct and is left as-is.

Tests

• useCollaboration.test.ts: buildProbeUrl produces /<token>/<room>; the hook dials /__probe__, not the bare URL.
• collabNoDoubling.test.tsx (new): mounts a real EditorView + the real yCollab binding (only the websocket transport faked). After binding + sync the editor holds the body exactly once for the seeder (fresh room) and a joiner (content arriving over the wire), with a regression guard proving that initializing the editor with the body reproduces the doubling.

Playwright verification (two contexts, same room)

Ran the dev server with the real worker (NEXT_PUBLIC_YJS_WS_URL=wss://collab.noteser.app/<token>) and drove two browser contexts on the same room via the share link (?collab=<collabId>) — see e2e/_verify_collab.spec.ts.

• Before (root cause / unit regression guard): editor initialized with the body doubles it post-sync; bare-URL probe -> 403 -> pill "unreachable".
• After (observed, green run): pill shows "Live: on"; opening the note shows the body exactly once in both clients; typing in context A appears live in context B; the content saved back to the store is the single correct body; no CSP/WebSocket console errors.

Gates

npm run lint clean · npx tsc --noEmit zero errors · full jest --ci green (3008 passed, no flake).

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