the live log showed the client requesting a full sector state every
500ms - one per turn, in lockstep with the heartbeat. the heartbeat
verifies the client's predicted checksum against ours, and the sim is
not yet bit-exact, so most turns mismatch, flip the client out of sync,
and it re-downloads the whole state. that resync storm is the "86%,
70%..." loading flicker at battle start and it hard-resets the battle
scene every turn, so nothing on screen can settle.
the heartbeat now stays off unless SCROLL_HEARTBEAT=1. this returns the
client to the snapshot-only path (a hard reset every 4 ticks, but no
per-turn off-sync request). turn it back on once checksums reliably
agree.
c18ce37a42