A peer's cursor now rides the live tip while drawing. The cursor and the in-progress shape travelled on two throttles at different rates (100 ms vs 80 ms) with no ordering between them, so the dot lagged the dragged corner by up to hundreds of milliseconds — sitting mid-edge while the tip moved on. Every pointermove now POSTs one fused ephemeral frame (normalized cursor plus the whole shape); peers render dot and corner from the same instant, so they cannot skew apart.
A retried frame no longer drags the dot back in time. The presence retry re-sent the original body up to 600 ms later and the receiver applied it unconditionally, so a late retry overwrote fresher positions. Frames carry the sender-captured cts (new PresenceMsg field, relayed untouched — the server still re-stamps only ts) and a per-user guard drops anything older than the last applied frame, for cursor and draft alike. Covered by two red-proofed two-context Playwright tests (dot-on-tip while held; aborted-frame retry exercised and dropped).