Validate save imports by main-data checksum, not raw file size

The SAVE FILES card only accepted saves of exactly 32768 bytes and
refused anything else. importToSlot now classifies a non-32768 file by
the integrity of its main-data checksum instead:

- Oversize + valid checksum -> an emulator RTC footer, so the launcher
  asks for confirmation, then truncates to 32768 on force.
- Oversize + invalid checksum -> rejected.
- Undersize + valid checksum -> imports zero-padded; otherwise refused.

Adds the "Oversized save file" confirm modal, a new vendor-oracle test
built by gen1lib (PKHeX-derived) run as its own Lua 5.4 tier, oversize/
truncated policy tests, and the LUA54 wiring in test.sh.

# Conflicts:
#	src/import/LauncherView.lua

src/import/LauncherView.lua

@@ -1505,6 +1505,8 @@ local function buildConfirmModal(imp, m)
           imp:_confirmModUpdate(c.id, c.release)
         elseif c.kind == "enableAll" then
           imp:_setAllMods(true, true)
+        elseif c.kind == "importOversize" then
+          imp:_importSave(c.version, c.source, true)
         else
           imp:_toggleMod(c.id, true)
         end

src/import/RomImporter.lua

@@ -1564,7 +1564,7 @@ end
 -- the target tab forward so the notice (and, on success, the new active slot)
 -- is visible.  Requires the ROM to be imported first, since a save is only
 -- playable with its game's data present.
-function RomImporter:_importSave(version, source)
+function RomImporter:_importSave(version, source, force)
   if self.workState == "working" then return end
   if GameVersion.VERSIONS[self.tab] or self.tab == "mods" then
     self.tab = version
@@ -1574,15 +1574,35 @@ function RomImporter:_importSave(version, source)
       .. GameVersion.info(version).displayName .. " ROM before importing a save." }
     return
   end
-  local ok, res = require("src.import.SaveFileIO").importToSlot(source, version)
+  local ok, res, info = require("src.import.SaveFileIO").importToSlot(source, version, force)
   if ok then
     self:_refreshSlots(version)
     self.activeSlot[version] = res
     self.slotScroll[version] = math.huge   -- pin the new row on screen (clamped in draw)
     self.saveNotice[version] = { ok = true, text = "Imported save into " .. tostring(res) .. "." }
-  else
-    self.saveNotice[version] = { ok = false, text = tostring(res) }
+    return
   end
+  if res == nil and info and info.needsConfirm then
+    -- A .sav larger than 32 KB whose first 32768 bytes checksum: the surplus
+    -- is almost certainly an emulator RTC footer, so ask before truncating.
+    -- The yes arm re-enters with force=true; cancel leaves the file untouched.
+    self._modConfirm = {
+      kind = "importOversize",
+      version = version,
+      source = source,
+      title = "Oversized save file",
+      lines = {
+        ("This save is %d bytes; a cartridge save is exactly %d bytes (32 KB).")
+          :format(info.size, 32768),
+        "It may come from a ROM that saved the battery image with an emulator.",
+        "The extra bytes would be discarded.",
+        "Import it anyway?",
+      },
+      yesLabel = "Import anyway",
+    }
+    return
+  end
+  self.saveNotice[version] = { ok = false, text = tostring(res) }
 end
 
 -- "Import save" button: open a native .sav picker and import the pick.

src/import/SaveFileIO.lua

@@ -64,18 +64,34 @@ local function readSource(source)
   return nil, "could not read the save file: " .. tostring(openErr)
 end
 
--- importToSlot(source, version) -> ok, slotIdOrErr
--- source: an absolute path, a LOVE DroppedFile, or raw 32768 bytes.  On success
+-- importToSlot(source, version, force) -> ok, slotIdOrErr | (false, nil, info)
+-- source: an absolute path, a LOVE DroppedFile, or raw bytes.  On success
 -- registers a new slot for the version, writes the imported save into it, makes
 -- it the active slot, and returns true + the new slot id.  On any failure
--- returns false + a friendly message.
-function SaveFileIO.importToSlot(source, version)
+-- returns false + a friendly message.  force only matters for a file LARGER
+-- than 32768 bytes whose first 32768 bytes carry a valid main-data checksum
+-- (i.e. a cartridge save padded with an emulator RTC footer): without force
+-- this returns false, nil, { needsConfirm = true, size = #bytes } so the
+-- launcher can ask the player before truncating; with force the extra bytes
+-- are dropped and the 32768-byte save imports.
+function SaveFileIO.importToSlot(source, version, force)
   version = version or GameVersion.get()
   local bytes, readErr = readSource(source)
   if not bytes then return false, readErr end
   if #bytes ~= SAVE_SIZE then
-    return false, ("A save file must be %d bytes (32 KB); this one is %d.")
-      :format(SAVE_SIZE, #bytes)
+    local check = SaveConvert.mainChecksumValid(bytes)
+    if check == nil then
+      return false, ("A save file must be %d bytes (32 KB); this one is %d.")
+        :format(SAVE_SIZE, #bytes)
+    end
+    if check == false then
+      return false, "save data checksum invalid (main data checksum mismatch)"
+    end
+    if #bytes > SAVE_SIZE and not force then
+      return false, nil, { needsConfirm = true, size = #bytes }
+    end
+    bytes = #bytes > SAVE_SIZE and bytes:sub(1, SAVE_SIZE)
+      or (bytes .. string.rep("\0", SAVE_SIZE - #bytes))
   end
   -- 3rd arg: the crosswalk has to come from THIS game's ROM cache.  The
   -- launcher imports before the cache is mounted on the un-prefixed paths, so