feat(mods): expose opt-in final-frame output hooks

tests/engine/gate_gen2_mod_api.lua

@@ -434,7 +434,8 @@ local GEN2_HOOKS = {
   -- pointer with the touch overlay given first refusal, the palette zone list
   -- handed to the present pass, the letterbox and the HUD rect.
   "input.step", "input.pointer",
-  "render.zones", "render.compose", "render.letterbox", "render.hud",
+  "render.zones", "render.compose", "render.output_enabled", "render.output",
+  "render.letterbox", "render.hud",
 }
 
 local function assertShared(name, sites, kind)

tests/engine/gen2_render_output_seam.lua

@@ -0,0 +1,47 @@
+package.path = "./?.lua;./?/init.lua;" .. package.path
+
+local T = require("tests.modkit")
+local Game2 = require("src.core.Game2")
+local Runtime = require("src.mods.Runtime")
+local Hooks = require("src.mods.Hooks")
+
+local savedHooks = Runtime.hooks
+local hooks = Hooks.new()
+Runtime.hooks = hooks
+
+local received
+hooks:wrap("render.output", function(_, context)
+  received = context
+  return true
+end, 0, "test")
+hooks:wrap("render.output_enabled", function() return false end, 0, "test")
+
+local canvas = love.graphics.newCanvas(640, 480)
+local presentCalls = 0
+local game = setmetatable({
+  frameFit = function() return 3, 80, 24, 1, 480, 432 end,
+  presentCanvas = function() presentCalls = presentCalls + 1 return canvas end,
+  drawScene = function() end,
+  drawHud = function() end,
+}, Game2)
+
+Game2.draw(game)
+T.eq(received, nil, "a disabled Gold output hook does not run")
+T.eq(presentCalls, 0, "a disabled Gold output hook keeps the direct path")
+
+hooks:wrap("render.output_enabled", function() return true end, 10, "test")
+Game2.draw(game)
+T.check(received ~= nil, "Gold raises render.output for an enabled subscriber")
+T.eq(received and received.canvas, canvas,
+  "Gold hands render.output the finished present canvas")
+T.eq(received and received.generation, 2,
+  "Gold identifies the output context without changing Gen 1")
+T.eq(received and received.gameX, 80, "Gold output carries the fitted game X")
+T.eq(received and received.gameY, 24, "Gold output carries the fitted game Y")
+T.eq(received and received.gameWidth, 480,
+  "Gold output carries the fitted game width")
+T.eq(received and received.gameHeight, 432,
+  "Gold output carries the fitted game height")
+
+Runtime.hooks = savedHooks
+T.finish("gen2 render output seam")