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Every mobile resume re-syncs read state and then schedules a read-state publish, whether or not anything changed. Each publish starts by downloading the full read-state snapshot (about 1 MB compressed on a heavy account) and only then finds nothing to send. Together with the re-sync's own snapshot, that is two full downloads per resume, and a third when a publish from before backgrounding retries. The publish now checks first, using the same packing it would publish, and returns before the snapshot when nothing is pending and no slot differs from what was last published. When something did change it behaves exactly as before, snapshot included. Today the snapshot fails before downloading on gzip-serving relays, so this only pays off once [#9089 read-state gzip fix](https://github.com/block/buzz/pull/9089) lands; without this PR, [#9089 read-state gzip fix](https://github.com/block/buzz/pull/9089) roughly doubles resume download on heavy accounts. It has no merge-order dependency. ### Validation - Added test: `a publish with nothing new skips the snapshot`. It publishes a change (one snapshot), publishes again with nothing new (no snapshot, no event), then publishes another change (snapshot and an event carrying both marks). It fails without the early return. - Existing read-state suite passes. - iPhone 12 mini, Profile build, Home backgrounded 12 s and resumed, all socket bytes received in the 15 s after resume: | Build | Download per resume | Snapshot fetches | | --- | --- | --- | | main (snapshot broken) | 3.07 MB | 0 completed | | [#9089 read-state gzip fix](https://github.com/block/buzz/pull/9089) | 6.85 MB | 3 | | [#9089 read-state gzip fix](https://github.com/block/buzz/pull/9089) + [#9090 no read-state replay](https://github.com/block/buzz/pull/9090) | 6.08 MB | 3 | | [#9089 read-state gzip fix](https://github.com/block/buzz/pull/9089) + [#9090 no read-state replay](https://github.com/block/buzz/pull/9090) + this | 2.71 MB | 1 | These are single runs on one account with 28 read-state slots, so treat the numbers as indicative. 🤖 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: studio <dc2fc481343672df31a689840c09299972e704dac592e0da6f18486646a7ee3e@buzz.block.builderlab.xyz>