The era's tenth category was a button in the tree that went nowhere. It now opens onto the
era's own per-addon enable list, rebuilt on show from the AddOn API: one checkbox per
installed addon carrying its `GetAddOnInfo` enabled state, then the Load out of date AddOns
row under it (`checkAddonVersion`, inverted, so checked means "0"). A toggle calls
`EnableAddOn`/`DisableAddOn`, which the host persists to `AddOns.txt` at logout — the
reference's own contract for this screen, where the change lands on the next world entry.
`the_defaults_button_is_armed_by_rows_not_by_a_category` is the invariant that every
category leads somewhere and that Defaults is live on every page with a CVar behind it, and
AddOns is the second category to run its own page after Keybindings. It is exempted from the
`OPTIONS_PAGE_ROWS` half for that reason, and from the Defaults half because an addon's
enabled state is not a CVar: there is nothing there for Defaults to write back.
chairmanpow
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