Hover Master First Aid - Doctor in the House in the bags and the box said the
name, the item level and "Requires First Aid (300)". The line it is carried
for, "Use: Teaches you advanced first aid, allowing a maximum of 375 first aid
skill.", was not there at all.

That line is not the item's. It is the spell's own sentence printed on the
item, and the client does not hold every spell's text at all times: it fetches
one when something asks for it and leaves the line off the tooltip until it
lands. A potion or a trinket reads correctly on the first hover because its
spell is already on the machine. A book teaching something nobody has ever
cast is the case where nothing ever asked, which is why this went unnoticed
while every other Use line in the addon was right.

UI/Scan.lua reads a tooltip once, at the moment the pointer arrives. Thin in
UI/Tip.lua already rebuilds a box that was waiting on an item and could not see
this one: the head band had lines in it and none of them was
RETRIEVING_ITEM_INFO. A box that looks finished and is not needs a second
question rather than a second reading of the same one.

So Scan.Waiting asks it. The item's spell id, whether its text is here, and the
request for one that is not, which are the three calls Syndicator makes on this
client in Search/CheckItem.lua. Thin counts a box waiting on that spell as
thin, SPELL_DATA_LOAD_RESULT joins GET_ITEM_INFO_RECEIVED on the frame that
drives the rebuild, and the box fills in where it stands. A worn slot carries
no link so one is asked for: a trinket you press has a Use line the same as a
book does, and the character sheet is nineteen hovers that all read a slot.

ns.ItemSpell hands back the id beside the name now. Nothing else reads it.

48-tooltip-arrival.lua is the gate, on a book fixture whose spell is not
cached: the first hover draws the client's own text without the Use line and
asks for the spell, and the sentence is in the box after the load lands. The
ask is asserted on its own, because a box that draws nothing and never asks is
a box that will draw nothing forever.

@@ -315,0 +368,4 @@
+	-- the text has landed, which is what UI/Tip.lua listens for.
+	local fetch = space.RequestLoadSpellData
+	if type(fetch) == "function" then
+		pcall(fetch, id)