LibTmux.Internal.FormatProjection.RowSeparator

Randomized per process, not fixed: a caller-controlled name (a window or pane) could otherwise embed a fixed separator deliberately. It carries no #, so tmux cannot expand it, and a value containing it fails decode loudly instead of corrupting a field.

Length is bounded by tmux's MAX_IMSGSIZE command cap, shared with the generation guard on every entity command: 22 hex digits balance collision odds against that budget.