Guarantee the post-battle fade-in by moving it into BattleState:finish()

pushBattle wrapped onFinish to push Transition.battleReturn on any
non-lose result, but that only fires for callers that route through
pushBattle correctly. Moving the same push into BattleState:finish()
instead -- the one choke point every battle (wild, trainer, walk-up,
scripted, link) already passes through on exit -- makes the fade
unconditional rather than dependent on each call site's wiring.

src/battle/BattleState.lua

@@ -4430,7 +4430,21 @@ function BattleState:finish()
   require("src.core.Music").restoreMap(self.data)
   self.game.stack:pop()
   Runtime.emit("battle.ended", { battle = self, result = self.result or "run" })
-  if self.onFinish then self.onFinish(self.result or "run") end
+  -- Coming back from the battle screen is a fade, not a cut: EnterMap sees
+  -- BIT_BATTLE_OVER_OR_BLACKOUT set and runs MapEntryAfterBattle
+  -- (home/overworld.asm:22, :749-753) = GBFadeInFromWhite.  This is the one
+  -- choke point every battle -- wild, trainer, walk-up, scripted, link --
+  -- passes through on its way out, so the fade is guaranteed here rather
+  -- than depending on each caller having wrapped onFinish correctly.
+  local result = self.result or "run"
+  local onFinish = self.onFinish
+  if result == "lose" then
+    -- the blackout path warps to the heal point with its own transition
+    if onFinish then onFinish(result) end
+    return
+  end
+  self.game.stack:push(require("src.render.Transition").battleReturn(self.game,
+    function() if onFinish then onFinish(result) end end))
 end
 
 -- ---------------------------------------------------------------------

src/world/OverworldController.lua

@@ -718,32 +718,10 @@ function OverworldState:pushBattle(battle)
     require("src.core.Music").playBattle(Game.data, battle:computeMusicKind())
   end
 
-  -- Coming back from the battle screen is a fade, not a cut: EnterMap sees
-  -- BIT_BATTLE_OVER_OR_BLACKOUT set and runs MapEntryAfterBattle
-  -- (home/overworld.asm:22, :749-753) = GBFadeInFromWhite, behind the
-  -- `ld c, 10 / call DelayFrames` at :351-352.
-  --
-  -- It is wrapped around onFinish here, at the one funnel every battle goes
-  -- through, rather than inside afterBattle: a script-driven win defers
-  -- afterBattle into ctx.afterScript so an evolution screen cannot be buried
-  -- under the trainer's follow-up text (see Commands.start_battle), and the
-  -- fade inherited that deferral -- on a rival battle it fired after the
-  -- post-battle dialogue AND the walk-off, instead of when the battle ended.
-  --
-  -- The rest of onFinish runs as the fade's onDone, which is also the
-  -- hardware order: MapEntryAfterBattle fades the map back in, and only then
-  -- does the map script get to run.  The overworld is frozen meanwhile --
-  -- StateStack updates the top state only -- so nothing moves under it.
-  local finish = battle.onFinish
-  battle.onFinish = function(result)
-    if result == "lose" then
-      -- the blackout path warps to the heal point with its own transition
-      if finish then finish(result) end
-      return
-    end
-    Game.stack:push(require("src.render.Transition").battleReturn(Game,
-      function() if finish then finish(result) end end))
-  end
+  -- The fade back in from white on the way out is BattleState:finish()'s
+  -- job now -- the one choke point every battle passes through on exit,
+  -- guaranteed regardless of which caller pushed the battle -- so this
+  -- function only owns the entry wipe.
   Game.stack:push(BattleTransition.new(Game, function()
     Game.stack:push(battle)
   end, {