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## Summary Every read-state resync (each reconnect and each resume from background) fetches every read-state blob (kind 30078, `#t: read-state`) from the past week, then opens a live subscription with no `since`, which replays the same blobs again. Merging keeps the newest mark per context, so blobs from before the previous fetch add nothing. Each blob is a whole device's read marks, about 100KB for a heavy reader. A later fetch and the live subscription now start `relayCrossDeviceSkewSeconds` (1860s) before the last successful fetch was sent. The relay rejects a `created_at` more than 900s from its clock, and blobs come from other devices, so a writer 900s slow and this phone 900s fast are at most 1800s apart. Every blob stored since that fetch falls inside the window. A failed fetch keeps the earlier start. The first fetch of a manager still covers the whole horizon. Companion to [#8901](https://github.com/block/buzz/pull/8901) and [#8902](https://github.com/block/buzz/pull/8902), which do the same for the unread catch-up and the latest-message query. Measured on an iPhone 12 mini against the internal relay, resuming after 60s in the background (kind 30078 websocket bytes, instrumented profile build): | | main | this PR | | --- | --- | --- | | Read-state resync on resume | about 1.8MB (91 blobs, fetch plus subscription replay) | 415KB (4 blobs changed since the last fetch) | ## Testing - New test: the first fetch covers the horizon, the live subscription and later fetches start 1860s before the last successful fetch was sent, and a failed fetch keeps that start. Confirmed it fails without the fix and with the earlier 960s window. - New test: after the clock moves back, a resync whose fetch fails isn't retried on every later read; the next reconnect fetches the whole horizon. Confirmed it fails without the fix. - `just mobile-check` and `just mobile-test` pass. - Device: resumed the app on the 12 mini on Wi-Fi; the resync fetched only the 4 blobs stored since the previous fetch, and the live subscription replayed none. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Signed-off-by: Tom Brow <tomb@squareup.com> Co-authored-by: Tom Brow <tomb@squareup.com> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>