fix: block y-websocket auto-reconnect during async IMS refresh

[chrischrischris]

Why

Three remaining bugs around the IMS token refresh path that survived #937 / #941. Together they explain a continuous baseline of HEAD 401s on da-admin (660k/day in Coralogix) even after those PRs landed.

Bug 1 — Race between async refresh and y-websocket's 100ms reconnect timer

y-websocket's onclose schedules setTimeout(setupWS, 2^wsUnsuccessfulReconnects * 100ms) synchronously. On a 4401 close the upgrade returns 101 + immediate close, so onopen briefly fires and wsUnsuccessfulReconnects stays at 0 — backoff is 100ms, shorter than a typical adobeIMS.refreshToken() round-trip. The auto-reconnect fired with the still-stale token and burned 2–3 HEAD 401s on da-admin per token expiry per tab.

Bug 2 — Concurrent close handlers racing lastSentToken

Because bug 1 produced multiple 4401 closes back-to-back, multiple async handlers ran concurrently. Handler A finishes first and writes lastSentToken = X2. Handler B (started during A's await) then sees fresh === lastSentToken (X2 === X2) and incorrectly concludes "no new token", sets shouldConnect = false, and shows the auth banner — even though the refresh worked.

Bug 3 — checkDoc doubles the HEAD volume on auth-close

createAwarenessStatusWidget has a second connection-close listener that calls checkDoc(path) → daFetch(path, { method: 'HEAD' }) on every close. On a 4401/4403 the doc is fine — da-collab signalled an auth failure — so this just fires another HEAD on da-admin which daFetch's refresh-and-retry compounds further.

What

• Flip shouldConnect=false synchronously before the first await in the close handler. The pending setTimeout(setupWS) becomes a no-op, eliminating bugs 1 and 2 (no concurrent close handlers because no auto-reconnects fire during the refresh window).
• Drive the reconnect ourselves via provider.connect() once we have the fresh token.
• Skip checkDoc when the close code is 4401/4403.

Trust model

Unchanged. 4403 still stops reconnection. 4401 with no new token still bails and surfaces the modal. Anonymous users still bail without showing the modal.

Tests

• New: Blocks y-websocket auto-reconnect during the in-flight refresh on 4401 — controls refreshToken via an unresolved promise and asserts shouldConnect===false during the await, then true after.
• New: Skips checkDoc HEAD on auth-close codes (4401/4403) — patches window.fetch and asserts no HEAD is issued on 4401/4403, but is on 1006.
• All existing close-handler tests still pass.

🤖 Generated with Claude Code

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• c0e3fd6 ✅ (latest)