feat(switch): switch handheld 720p / docked 1080p at runtime

Unlock love-nx SDL dock/undock resizing and sync via NxDisplay so
booting docked is not stuck on the conf 720p hint.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/core/NxDisplay.lua

@@ -0,0 +1,96 @@
+-- Switch-only display size: handheld 1280x720, docked (TV) 1920x1080.
+-- love-nx's SDL backend can auto-resize on dock/undock when the window is
+-- resizable; this module also syncs on boot and every frame so a docked
+-- launch is not stuck at the conf.lua 720p hint until the next mode change.
+
+local Platform = require("src.core.Platform")
+
+local NxDisplay = {}
+
+NxDisplay.HANDHELD_W, NxDisplay.HANDHELD_H = 1280, 720
+NxDisplay.DOCKED_W, NxDisplay.DOCKED_H = 1920, 1080
+
+-- AppletOperationMode from libnx: Handheld = 0, Console (docked) = 1.
+local MODE_HANDHELD = 0
+local MODE_CONSOLE = 1
+
+-- Test hooks (nil = use live Platform / FFI / love.window).
+NxDisplay._forceNXForTests = nil
+NxDisplay._operationModeForTests = nil
+
+local ffiOk, ffiC
+
+local function ensureFfi()
+  if ffiOk ~= nil then return ffiOk end
+  ffiOk = false
+  local ok, ffi = pcall(require, "ffi")
+  if not ok or not ffi then return false end
+  -- Redefinition is fine across hot reload / tests; we only need the symbol.
+  pcall(ffi.cdef, [[
+    unsigned char appletGetOperationMode(void);
+  ]])
+  local probeOk = pcall(function()
+    return ffi.C.appletGetOperationMode
+  end)
+  if not probeOk then return false end
+  ffiC = ffi.C
+  ffiOk = true
+  return true
+end
+
+local function isNX()
+  if NxDisplay._forceNXForTests ~= nil then
+    return not not NxDisplay._forceNXForTests
+  end
+  return Platform.isNX()
+end
+
+-- Returns AppletOperationMode or nil when unavailable.
+function NxDisplay.operationMode()
+  if NxDisplay._operationModeForTests ~= nil then
+    return NxDisplay._operationModeForTests
+  end
+  if not ensureFfi() or not ffiC then return nil end
+  local ok, mode = pcall(function()
+    return tonumber(ffiC.appletGetOperationMode())
+  end)
+  if not ok then return nil end
+  return mode
+end
+
+-- Map operation mode → framebuffer size. Unknown / nil → handheld 720p.
+function NxDisplay.desiredSize(mode)
+  if mode == nil then mode = NxDisplay.operationMode() end
+  if mode == MODE_CONSOLE then
+    return NxDisplay.DOCKED_W, NxDisplay.DOCKED_H
+  end
+  return NxDisplay.HANDHELD_W, NxDisplay.HANDHELD_H
+end
+
+-- Apply handheld/dock size when on NX and the window differs. No-op elsewhere.
+-- Returns true when setMode ran.
+function NxDisplay.sync()
+  if not isNX() then return false end
+  if not (love and love.window and love.window.getMode and love.window.setMode) then
+    return false
+  end
+  local wantW, wantH = NxDisplay.desiredSize()
+  local curW, curH, flags = love.window.getMode()
+  flags = flags or {}
+  if curW == wantW and curH == wantH
+     and flags.fullscreen == false and flags.resizable == true then
+    return false
+  end
+  flags.fullscreen = false
+  flags.resizable = true
+  love.window.setMode(wantW, wantH, flags)
+  return true
+end
+
+function NxDisplay._resetForTests()
+  NxDisplay._forceNXForTests = nil
+  NxDisplay._operationModeForTests = nil
+  ffiOk, ffiC = nil, nil
+end
+
+return NxDisplay