Baseline hygiene

Since the linking key is the start height (V3, content), it is enough to obfuscate the start. Both approaches cost only re-downloaded blocks and work in every configuration.

• Randomized overlap: start a random number of blocks before the true resume point, re-fetching blocks already held, so starts stop being exact pointers to previous ends and chaining degrades to approximate, deniable joins.
• Checkpoint snapping: round the start down to a standard checkpoint (an absolute height), so every client whose previous sync ended in the same checkpoint interval emits an identical start — the collision window grows from one block interval to the checkpoint spacing.

Broadcast timing is a V2 (timing) leak at the destination. In-transit mixing does not remove it — the destination still observes wall-clock arrival time — so the wallet must decorrelate broadcasts itself.

• Never send a broadcast over the sync transport or session.
• Decorrelate broadcast times from sync milestones — in particular, do not broadcast immediately upon reaching the tip.
• Use a randomized timer for broadcasts (the note's Defense B for migration rounds), extended to every broadcast.
• Destination splitting: sync from one lightwalletd and broadcast through another.

How aggressively to obfuscate the start is a design choice with a clear qualitative shape but no settled numbers. A larger overlap, or a wider checkpoint spacing, widens the collision window — and therefore the anonymity set of clients emitting an indistinguishable start — at the cost of more re-downloaded blocks. Both approaches cost only re-downloaded blocks and apply in every configuration.

• Trade-off: wider overlap / spacing ⇒ larger anonymity set, but more wasteful re-download.
• Open question: how to set the overlap distribution or the checkpoint spacing, and what each buys quantitatively in terms of anonymity-set size, is left open by the source note — presented here without fixed values.