nameplates: let each plate watch its own unit

The central handler registered UNIT_AURA, UNIT_FLAGS and the four
UNIT_SPELLCAST_* globally, so every unit event in the world woke it for a
"^nameplate" prefix test, and each of the four branches that survived the test
then resolved the plate back out of arg1 -- UnitGUID + plateByGuid, or
GetNamePlateForUnit.

Register them per plate instead, on the plate's own frame against its own
token. The token is the subscription, so the event only reaches the plate it
concerns and `this` is already that plate: the aura branch is now one
assignment where it used to be a prefix test, an API call and a table lookup.

This is also what makes the approach viable at all. A central listener would
have had to name every token it might care about, and nameplate slots have no
cap -- Events.cpp keeps them in a vector that grows by push_back, with only a
"<80 even in AV-scale scenes" comment for sizing. Any nameplate1..N list would
have been a guess that fails silently in exactly the crowded scenes where
plates matter.

Lifecycle: NAME_PLATE_UNIT_ADDED points the registrations at the new token,
replacing the previous unit rather than stacking, since RegisterUnitEvent over
an already-filtered registration swaps the units. NAME_PLATE_UNIT_REMOVED
unregisters, which is required -- freed slots are reused, and a stale token
would feed the frame another unit's events.

PLAYER_LOGOUT now tears down the plates too. It silenced only the central
frame before; leaving forty plate frames dispatching through logout is the
crash 132 that branch exists to prevent.

modules/nameplates.lua

@@ -5,10 +5,7 @@ pfUI:RegisterModule("nameplates", function ()
   -- Local function references for performance
   local GetTime = GetTime
   local UnitName = UnitName
-  local UnitClass = UnitClass
-  local UnitLevel = UnitLevel
   local UnitIsPlayer = UnitIsPlayer
-  local UnitIsDead = UnitIsDead
   local UnitAffectingCombat = UnitAffectingCombat
   local UnitIsUnit = UnitIsUnit
   local UnitCanAssist = UnitCanAssist
@@ -498,13 +495,10 @@ nameplates:RegisterEvent("PARTY_MEMBERS_CHANGED")
 nameplates:RegisterEvent("NAME_PLATE_CREATED")
 nameplates:RegisterEvent("NAME_PLATE_UNIT_ADDED")
 nameplates:RegisterEvent("NAME_PLATE_UNIT_REMOVED")
-nameplates:RegisterEvent("UNIT_AURA")
-nameplates:RegisterEvent("UNIT_FLAGS")
 nameplates:RegisterEvent("UPDATE_MOUSEOVER_UNIT")
-nameplates:RegisterEvent("UNIT_SPELLCAST_START")
-nameplates:RegisterEvent("UNIT_SPELLCAST_CHANNEL_START")
-nameplates:RegisterEvent("UNIT_SPELLCAST_STOP")
-nameplates:RegisterEvent("UNIT_SPELLCAST_CHANNEL_STOP")
+-- UNIT_AURA / UNIT_FLAGS / UNIT_SPELLCAST_* are registered per plate, on the
+-- plate's own frame, against its own token -- see OnCreate and
+-- NAME_PLATE_UNIT_ADDED.
 nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
   
   nameplates:SetScript("OnEvent", function()
@@ -516,6 +510,15 @@ nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
       if nameplates.mouselook then
         nameplates.mouselook:SetScript("OnUpdate", nil)
       end
+      -- The plates hold their own unit subscriptions now, so silencing this
+      -- frame alone would leave them dispatching through logout -- exactly what
+      -- this branch exists to prevent.
+      for plate in pairs(registry) do
+        if plate.nameplate then
+          plate.nameplate:UnregisterAllEvents()
+          plate.nameplate:SetScript("OnEvent", nil)
+        end
+      end
       return
 
     elseif event == "PLAYER_GUILD_UPDATE" and arg1 == 'player' then
@@ -591,6 +594,16 @@ nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
         local guid = UnitGUID(arg1)
         plate.nameplate.cachedGuid = guid
         plate.nameplate.unit = arg1
+
+        -- Point this plate's own subscriptions at the token it just took. On a
+        -- recycled frame these replace the previous unit rather than stacking:
+        -- RegisterUnitEvent on an already-filtered registration swaps the units.
+        plate.nameplate:RegisterUnitEvent("UNIT_AURA", arg1)
+        plate.nameplate:RegisterUnitEvent("UNIT_FLAGS", arg1)
+        plate.nameplate:RegisterUnitEvent("UNIT_SPELLCAST_START", arg1)
+        plate.nameplate:RegisterUnitEvent("UNIT_SPELLCAST_CHANNEL_START", arg1)
+        plate.nameplate:RegisterUnitEvent("UNIT_SPELLCAST_STOP", arg1)
+        plate.nameplate:RegisterUnitEvent("UNIT_SPELLCAST_CHANNEL_STOP", arg1)
         plate.nameplate.creatureType = nil  -- recompute for the new unit
         plate.nameplate.totemIcon = nil
         plate.nameplate.totemSpell = nil
@@ -621,14 +634,9 @@ nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
         if plate and plate.nameplate and plate.nameplate.cachedGuid == guid then
           plate.nameplate.cachedGuid = nil
           plate.nameplate.unit = nil
-        end
-      end
-
-    elseif event == "UNIT_FLAGS" then
-      if arg1 and strfind(arg1, "^nameplate") then
-        local plate = C_NamePlate.GetNamePlateForUnit(arg1)
-        if plate and plate.nameplate then
-          plate.nameplate.eventcache = true
+          -- Drop the subscriptions with the token: this slot is now free and the
+          -- next plate to take it would otherwise feed this frame its events.
+          plate.nameplate:UnregisterAllEvents()
         end
       end
 
@@ -643,48 +651,6 @@ nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
         if pn then pn.eventcache = true end
       end
 
-    elseif event == "UNIT_SPELLCAST_START" or event == "UNIT_SPELLCAST_CHANNEL_START" then
-      -- ClassicAPI fires UNIT_SPELLCAST_* per unit token, including the caster's
-      -- "nameplateN". The payload has no timing, so poll it (PollCastInfo picks
-      -- cast vs channel) and cache -- only for a unit we have a plate for, so
-      -- the table stays bounded to on-screen casters.
-      if arg1 and strfind(arg1, "^nameplate") then
-        local guid = UnitGUID(arg1)
-        local plate = guid and plateByGuid[guid]
-        if plate then
-          castState[guid] = PollCastInfo(arg1)
-          if castState[guid] then
-            plate.castUpdate = true  -- bypass the throttle so the bar shows now
-          end
-        end
-      end
-
-    elseif event == "UNIT_SPELLCAST_STOP" or event == "UNIT_SPELLCAST_CHANNEL_STOP" then
-      -- Cast/channel ended (natural, interrupted, or cancelled -- the poll fires
-      -- STOP for all three). Clear the cached cast and refresh its plate.
-      if arg1 and strfind(arg1, "^nameplate") then
-        local guid = UnitGUID(arg1)
-        if guid and castState[guid] then
-          castState[guid] = nil
-          local plate = plateByGuid[guid]
-          if plate then plate.castUpdate = true end
-        end
-      end
-
-    elseif event == "UNIT_AURA" then
-      -- ClassicAPI: fires with arg1 == "nameplateN" when a unit's aura set
-      -- changes (add/remove/modify). Flag the matching plate so OnUpdate does a
-      -- fresh C_UnitAuras read next tick instead of waiting on the 0.5s
-      -- throttle -- covers expirations, dispels, refreshes, and stack changes
-      -- in one event. Guard on the token prefix (UNIT_AURA also fires for
-      -- target/party/raid).
-      if arg1 and strfind(arg1, "^nameplate") then
-        local plate = C_NamePlate.GetNamePlateForUnit(arg1)
-        if plate and plate.nameplate then
-          plate.nameplate.auraUpdate = true
-        end
-      end
-
     elseif event == "PLAYER_TARGET_CHANGED" then
       frameState.targetGuid = UnitGUID('target')
       -- Flag the target's plate for update
@@ -766,6 +732,40 @@ nameplates:RegisterEvent("PLAYER_GUILD_UPDATE")
     nameplate.cache = {}
     nameplate.original = {}
 
+    -- Each plate watches its own unit. With RegisterUnitEvent the token IS the
+    -- subscription, so there is no central listener sifting every unit event in
+    -- the world for a "^nameplate" prefix and then resolving the plate back out
+    -- of arg1 -- the event arrives only at the plate it concerns, and `this` is
+    -- already that plate. NAME_PLATE_UNIT_ADDED points the registration at the
+    -- new token; _REMOVED drops it, which matters because freed slots are
+    -- reused and a stale token would feed this frame another unit's events.
+    nameplate:SetScript("OnEvent", function()
+      if event == "UNIT_AURA" then
+        -- a fresh C_UnitAuras read next tick rather than waiting out the 0.5s
+        -- throttle -- covers expiry, dispels, refreshes and stack changes
+        this.auraUpdate = true
+      elseif event == "UNIT_FLAGS" then
+        this.eventcache = true
+      elseif event == "UNIT_SPELLCAST_START" or event == "UNIT_SPELLCAST_CHANNEL_START" then
+        -- the payload carries no timing, so poll it (PollCastInfo picks cast
+        -- vs channel)
+        local guid = this.cachedGuid
+        if guid then
+          castState[guid] = PollCastInfo(this.unit)
+          if castState[guid] then
+            this.castUpdate = true -- bypass the throttle so the bar shows now
+          end
+        end
+      elseif event == "UNIT_SPELLCAST_STOP" or event == "UNIT_SPELLCAST_CHANNEL_STOP" then
+        -- ended: natural, interrupted or cancelled -- the poll fires STOP for all
+        local guid = this.cachedGuid
+        if guid and castState[guid] then
+          castState[guid] = nil
+          this.castUpdate = true
+        end
+      end
+    end)
+
     -- create shortcuts for all known elements and disable them
     nameplate.original.healthbar, nameplate.original.castbar = parent:GetChildren()
     DisableObject(nameplate.original.healthbar)