`SetFont` raised on a `false` flags argument and wrote the height even when the load failed, and only SimpleHTML had `SetSpacing`/`GetSpacing`, so SpellAlert's message frame raised in its OnLoad.
In 1.12.1 `SetFont` (`0x79f210`, the FontString's `0x79d4f0`) reads flags only when `lua_isstring` (`0x79f287`), writes them on every successful load (`0x79f334`), and writes nothing on a failed load or a height ≤ 0 (`0x79f361`, `0x79f2f4`, `0x771571`). Every text table has the spacing pair (`0x79fb40`/`0x79fbe0`; the FontString's clamps at `0x772240`); the line step adds the gap rounded up to a device pixel (`0x5c2070`, `0x5cdc20`), as do the message frames (`0x78899e`, `0x785f06`) and EditBox rows (`0x77d133`).
All seven SetFont bindings share these gates and ask the host's font probe; spacing is stored, inherited, measured and drawn on all six tables.
Tests bite on the parent for each.
Fixes#873Fixes#692Fixes#945🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
