diff --git a/.gitignore b/.gitignore
index 69581d85..16d74675 100644
--- a/.gitignore
+++ b/.gitignore
@@ -79,3 +79,9 @@ mobile/ios/bundle_id.local
 
 # Local options / preferences
 /options.lua*
+
+# User-owned ROMs imported for individual mods. Manifests declare the
+# destinations, but source checkouts and packaged mods never ship the files.
+/mods/*/baseroms/
+/imports/baseroms/
+/imports/baseroms-recovery/
diff --git a/docs/modding.md b/docs/modding.md
index 8a1a287c..19c88f0b 100644
--- a/docs/modding.md
+++ b/docs/modding.md
@@ -44,6 +44,25 @@ Every mod contains a root `manifest.json` defining its metadata, supported games
   "optional_dependencies": [
     "gen1_modern_ui"
   ],
+  "required_imports": [
+    {
+      "id": "stadium2",
+      "name": "Pokemon Stadium 2 ROM",
+      "description": "Pokemon Stadium 2 (USA), any supported N64 byte order",
+      "file": "stadium2.z64",
+      "format": "n64",
+      "size": 67108864,
+      "md5": ["00000000000000000000000000000000"]
+    }
+  ],
+  "optional_imports": [
+    {
+      "id": "bonus_source",
+      "name": "Optional bonus source",
+      "file": "bonus.bin",
+      "md5": "00000000000000000000000000000000"
+    }
+  ],
   "conflicts": [],
   "permissions": ["engine_internals"],
   "description": "A brief description of the mod.",
@@ -67,6 +86,8 @@ Every mod contains a root `manifest.json` defining its metadata, supported games
 | `priority` | `integer` | Load priority order (lower numbers load earlier; dependencies always precede dependents regardless of priority). |
 | `dependencies` | `array` | Hard required dependencies. A mod will not load if a required dependency is missing or disabled for the active game. |
 | `optional_dependencies` | `array` | Soft dependencies. Guarantees that if the target mod is present and active, it loads *before* this mod without blocking load if absent. |
+| `required_imports` | `array` | User-supplied files required by this mod. The launcher validates and copies each file into this mod's `baseroms/` directory; the mod does not load while one is missing. |
+| `optional_imports` | `array` | User-supplied files that unlock optional mod functionality. They use the same validation and private-copy flow but never block the mod from loading. |
 | `conflicts` / `incompatible` | `array` | List of mod IDs that cannot run concurrently with this mod. |
 | `permissions` | `array` | Requested privileges (e.g. `["engine_internals"]`, `["network"]`, `["filesystem"]`). |
 | `github` | `string` | GitHub repository (`"owner/repo"`) used for update checks and dependency download links. |
@@ -91,6 +112,42 @@ Dependencies in `dependencies` and `optional_dependencies` can be declared in se
 #### Version-Scoped Dependencies
 When a mod supports multiple games (`"games": ["gen1", "gen2"]`), a dependency can specify `"games": ["gen2"]` to indicate it is only required when booting Gen 2. When booting Gen 1, the engine will ignore the dependency, preventing unnecessary boot blocks on games that do not need it.
 
+### Required user-supplied files
+
+`required_imports` and `optional_imports` keep copyrighted or otherwise user-owned source material
+out of mod archives while giving every platform the same installation flow.
+Each object requires a stable `id`, a display `name`, a destination `file`
+(a filename, never a path), and one MD5 digest or an array of accepted MD5
+digests. `format` is either `"raw"` (the default) or `"n64"`. An optional
+`description` gives players dump or region guidance in the import panel.
+`size` declares the exact canonical byte length; `max_size` declares a smaller
+per-import ceiling when an exact size is not appropriate. Every import also
+has an engine-enforced 128 MiB ceiling and is rejected before hashing when its
+filesystem reports an invalid size.
+
+For `"n64"`, the launcher recognizes `.z64`, `.v64`, and `.n64` byte orders,
+strips a recognized 512-byte copier header, converts the bytes to canonical
+big-endian `.z64` order, and then checks MD5. The canonical bytes are written
+to `mods/<mod-id>/baseroms/<file>`. Each selection is a private grant to that
+mod: the launcher never scans or copies another mod's imported files merely
+because its manifest names the same digest. Mods read the result with their existing scoped `mod:read` API, for
+example `mod:read("baseroms/stadium2.z64")`; no host path or new filesystem
+permission is exposed. Missing `required_imports` block the mod before its
+entry chunk runs; missing `optional_imports` remain visible in the same
+launcher panel but do not block loading.
+
+MD5 here identifies a known dump because ROM databases commonly publish it;
+it is not a security or authenticity guarantee. Do not paste the SHA-1 used by
+Gen1Recomp's own game-ROM importer into an import's `md5` field. Mod archives
+must not include anything beneath `baseroms/`. The engine records a validation
+receipt keyed by file size and modification time so launcher refreshes and
+later boots do not repeatedly hash an unchanged imported ROM.
+
+New mobile code should call `love.system.pickFile("required_import")`. The
+older iOS-only `"stadium"` picker kind remains temporarily for compatibility.
+Android now returns `false` for unknown picker kinds instead of treating them
+as game-ROM picks.
+
 ## Mods and Gold (Gen 2)
 
 The mod API is one API across both generations, but Gold runs its own battle
diff --git a/mobile/android/love/src/jni/love/src/modules/system/System.cpp b/mobile/android/love/src/jni/love/src/modules/system/System.cpp
index b2b4ac5b..fce90d63 100644
--- a/mobile/android/love/src/jni/love/src/modules/system/System.cpp
+++ b/mobile/android/love/src/jni/love/src/modules/system/System.cpp
@@ -192,8 +192,14 @@ bool System::pickFile(const char *kind) const
 			dest = "picked_mod.zip";
 		else if (strcmp(kind, "sav") == 0 || strcmp(kind, "save") == 0)
 			dest = "picked_save.sav";
+		else if (strcmp(kind, "required_import") == 0)
+			dest = "picked_required_import.bin";
 		else if (strcmp(kind, "rom") == 0)
 			dest = "picked_rom.gb";
+		// Unknown kinds used to fall through to the ROM destination. Refuse them
+		// so a newer Lua caller cannot silently route an unrelated file as a ROM.
+		else
+			return false;
 	}
 	return love::android::showFilePicker(dest);
 #else
@@ -202,6 +208,15 @@ bool System::pickFile(const char *kind) const
 #endif
 }
 
+const char *System::pickFileKinds() const
+{
+#ifdef LOVE_ANDROID
+	return "rom,mod,sav,required_import";
+#else
+	return "";
+#endif
+}
+
 bool System::createFile(const char *suggestedName) const
 {
 #ifdef LOVE_ANDROID
diff --git a/mobile/android/love/src/jni/love/src/modules/system/System.h b/mobile/android/love/src/jni/love/src/modules/system/System.h
index ccf3538d..7ab0484a 100644
--- a/mobile/android/love/src/jni/love/src/modules/system/System.h
+++ b/mobile/android/love/src/jni/love/src/modules/system/System.h
@@ -112,10 +112,12 @@ public:
 	 * love::android::showFilePicker and src/import/RomImporter.lua.
 	 *
 	 * @param kind Optional pick kind: nullptr/"rom" -> picked_rom.gb,
-	 *             "mod" -> picked_mod.zip, "sav"/"save" -> picked_save.sav.
+	 *             "mod" -> picked_mod.zip, "sav"/"save" -> picked_save.sav,
+	 *             "required_import" -> picked_required_import.bin.
 	 * @return Whether the picker was shown.
 	 **/
 	virtual bool pickFile(const char *kind = nullptr) const;
+	virtual const char *pickFileKinds() const;
 
 	/**
 	 * Shows the platform's native "create / save a file" UI (Android SAF
diff --git a/mobile/android/love/src/jni/love/src/modules/system/wrap_System.cpp b/mobile/android/love/src/jni/love/src/modules/system/wrap_System.cpp
index fc8c2240..9dfa18ea 100644
--- a/mobile/android/love/src/jni/love/src/modules/system/wrap_System.cpp
+++ b/mobile/android/love/src/jni/love/src/modules/system/wrap_System.cpp
@@ -102,6 +102,12 @@ int w_pickFile(lua_State *L)
 	return 1;
 }
 
+int w_pickFileKinds(lua_State *L)
+{
+	luax_pushstring(L, instance()->pickFileKinds());
+	return 1;
+}
+
 int w_createFile(lua_State *L)
 {
 	const char *suggested = luaL_optstring(L, 1, nullptr);
@@ -222,6 +228,7 @@ static const luaL_Reg functions[] =
 	{ "openURL", w_openURL },
 	{ "vibrate", w_vibrate },
 	{ "pickFile", w_pickFile },
+	{ "pickFileKinds", w_pickFileKinds },
 	{ "createFile", w_createFile },
 	{ "syncHealthSteps", w_syncHealthSteps },
 	{ "restartApp", w_restartApp },
diff --git a/mobile/ios/native/GRPickerBridge.swift b/mobile/ios/native/GRPickerBridge.swift
index c571461b..b51925f6 100644
--- a/mobile/ios/native/GRPickerBridge.swift
+++ b/mobile/ios/native/GRPickerBridge.swift
@@ -5,7 +5,7 @@
 // without updating that patch (see mobile/ios/patch_love_src.py).
 //
 // Contract (mirrors love-android's GameActivity.showFilePicker):
-//   love.system.pickFile("rom"|"mod"|"sav") -> copies the user's pick into
+//   love.system.pickFile("rom"|"mod"|"sav"|"required_import") -> copies the user's pick into
 //   the LÖVE save directory as picked_rom.gb / picked_mod.zip /
 //   picked_save.sav; RomImporter's pending-file scan consumes it.
 //   love.system.createFile(name) -> exports save dir's pending_export.sav
@@ -83,6 +83,8 @@ public final class GRPickerBridge: NSObject {
             types = [.zip]
         case "sav":
             destName = "picked_save.sav"
+        case "required_import":
+            destName = "picked_required_import.bin"
         // A Nintendo 64 cartridge, for mods that build assets out of one --
         // the voxel mod's Pokemon Stadium battle models are the caller this
         // was added for. Its own filename on purpose: an N64 ROM landing on
@@ -135,7 +137,7 @@ public final class GRPickerBridge: NSObject {
     // Kept beside the switch it describes, because the two drifting apart is
     // the only way this can lie.
     @objc public static func supportedPickerKinds() -> NSString {
-        return "rom,mod,sav,stadium" as NSString
+        return "rom,mod,sav,stadium,required_import" as NSString
     }
 
     @objc(presentExportWithName:saveDir:)
diff --git a/mobile/ios/patch_love_src.py b/mobile/ios/patch_love_src.py
index e9a90a43..0ddbdc5b 100644
--- a/mobile/ios/patch_love_src.py
+++ b/mobile/ios/patch_love_src.py
@@ -89,7 +89,8 @@ int w_pickFile(lua_State *L)
 	return gr_callBridge(L, "GRPickerBridge", "presentPickerWithKind:saveDir:", kind);
 }
 
-// love.system.pickFileKinds() -> "rom,mod,sav,stadium", or nil off iOS.
+// love.system.pickFileKinds() -> the comma-separated kinds supported by the
+// Swift bridge (including required_import), or nil off iOS.
 //
 // So a caller can ask what this build's picker understands BEFORE opening it.
 // An unknown kind is refused (GRPickerBridge), and a refusal looks exactly
diff --git a/src/import/LauncherView.lua b/src/import/LauncherView.lua
index 05f66799..a8477d7e 100644
--- a/src/import/LauncherView.lua
+++ b/src/import/LauncherView.lua
@@ -638,6 +638,7 @@ end
 
 local function modStatusColor(status)
   if status == "ok" then return Strings("Ready"), PAL.green end
+  if status == "needs_import" then return Strings("Import required"), PAL.yellow end
   if status == "conflict" then return Strings("Conflict"), PAL.red end
   -- not a fault: the mod is intact, this is simply not a game it is for
   -- (src/mods/ModTargets.lua)
@@ -2767,11 +2768,14 @@ local function buildModActionsModal(imp, m)
   local hasGit = mod.github and mod.github ~= ""
   local depSpecs = mod.dependencySpecs or (mod.manifest and mod.manifest.dependencySpecs)
   local hasDeps = depSpecs and #depSpecs > 0
+  local imports = mod.imports or mod.requiredImports
+  local hasImports = imports and #imports > 0
   local info = hasGit and imp:_modUpdateInfo(mod.id)
   local pad = math.floor(18 * m.s)
   local w = math.floor(440 * m.s)
   local gap = math.floor(8 * m.s)
-  local nBtns = (hasGit and 2 or 0) + (hasDeps and 1 or 0) + 2
+  local nBtns = (hasGit and 2 or 0) + (hasDeps and 1 or 0)
+    + (hasImports and 1 or 0) + 2
   local h = pad + Kit.textHeight("button") + math.floor(4 * m.s)
     + Kit.textHeight("small") + math.floor(12 * m.s)
     + nBtns * (m.btnH + gap) - gap + pad
@@ -2821,6 +2825,19 @@ local function buildModActionsModal(imp, m)
         end })
     cy = cy + m.btnH + gap
   end
+  if hasImports then
+    local missing = tonumber(mod.missingRequiredImports) or 0
+    local label = missing > 0
+      and Strings("Imported files (%d required)", missing)
+      or Strings("Imported files")
+    btn(imp, px + pad, cy, pw - 2 * pad, m.btnH, "modact-imports",
+      label, { kind = missing > 0 and "warn" or "accent", font = "small",
+        action = function()
+          imp._modImports = id
+          imp._modActions = nil
+        end })
+    cy = cy + m.btnH + gap
+  end
   local armed = deleteArmed(imp, "mod", id, nil)
   btn(imp, px + pad, cy, pw - 2 * pad, m.btnH, "modact-del",
     DELETE_LABEL(armed), {
@@ -2837,6 +2854,109 @@ local function buildModActionsModal(imp, m)
       action = function() imp._modActions = nil end })
 end
 
+-- Imported files declared by one installed mod.  The engine picks, validates,
+-- canonicalizes and copies; this surface never exposes a host path to mod code.
+local function buildRequiredImportsModal(imp, m)
+  local mod
+  for _, candidate in ipairs(imp.mods or {}) do
+    if candidate.id == imp._modImports then mod = candidate break end
+  end
+  if not mod then imp._modImports = nil return end
+  local imports = mod.imports or mod.requiredImports or {}
+  local pad, gap = math.floor(18 * m.s), math.floor(8 * m.s)
+  local w = math.floor(540 * m.s)
+  local notice = imp.requiredImportNotice
+  if not notice or notice.modId ~= mod.id then notice = nil end
+  local noticeText
+  if notice then
+    local importName = notice.importId
+    for _, row in ipairs(imports) do
+      if row.id == notice.importId then importName = row.name break end
+    end
+    noticeText = Strings("%s rejected: %s", importName, notice.text)
+  end
+  local noticeW = w - 2 * pad
+  local noticeH = noticeText and Kit.wrapHeight("small", noticeText, noticeW, 2) or 0
+  local rowH = math.max(math.floor(70 * m.s), m.btnH)
+  local perPage = math.min(4, math.max(1, #imports))
+  local pagerH = #imports > perPage and math.max(Kit.tapMin(), math.floor(30 * m.s)) or 0
+  local h = pad + Kit.textHeight("button") + math.floor(4 * m.s)
+    + Kit.textHeight("small") + math.floor(12 * m.s)
+    + noticeH + (noticeH > 0 and gap or 0)
+    + perPage * rowH + math.max(0, perPage - 1) * gap
+    + (pagerH > 0 and (gap + pagerH) or 0) + gap + m.btnH + pad
+  local px, py, pw = modalPanel(m, w, h)
+  local cy = py + pad
+  Kit.text("button", Kit.ellipsize("button", mod.name, pw - 2 * pad),
+    px + pad, cy, PAL.heading)
+  cy = cy + Kit.textHeight("button") + math.floor(4 * m.s)
+  Kit.text("small", Strings("User-supplied files are validated by MD5 and copied into this mod only."),
+    px + pad, cy, PAL.muted)
+  cy = cy + Kit.textHeight("small") + math.floor(12 * m.s)
+  if noticeText then
+    cy = cy + Kit.textWrapped("small", noticeText, px + pad, cy,
+      pw - 2 * pad, PAL.red, 2) + gap
+  end
+
+  local pageKey = "required-imports-" .. mod.id
+  local cur = page(imp, pageKey)
+  local first, last, bounded = Kit.pageBounds(cur, #imports, perPage)
+  setPage(imp, pageKey, bounded)
+  for i = first, last do
+    local row = imports[i]
+    local importId = row.id
+    Kit.card(px + pad, cy, pw - 2 * pad, rowH, row.present and "muted" or false)
+    local innerX = px + pad + math.floor(12 * m.s)
+    local actionW = math.floor(108 * m.s)
+    local removeW = row.present and math.floor(86 * m.s) or 0
+    local actionX = px + pw - pad - math.floor(10 * m.s) - actionW
+    if removeW > 0 then actionX = actionX - removeW - math.floor(6 * m.s) end
+    local textW = actionX - innerX - math.floor(8 * m.s)
+    Kit.text("small", Kit.ellipsize("small", row.name, textW), innerX,
+      cy + math.floor(8 * m.s), PAL.heading)
+    local stateY = cy + math.floor(8 * m.s) + Kit.textHeight("small")
+      + math.floor(3 * m.s)
+    if row.description and row.description ~= "" then
+      Kit.text("micro", Kit.ellipsize("micro", row.description, textW),
+        innerX, stateY, PAL.muted)
+      stateY = stateY + Kit.textHeight("micro") + math.floor(2 * m.s)
+    end
+    local state = row.present and Strings("Ready - %s", row.file)
+      or (row.error and Strings("Invalid file - choose again")
+        or (row.required and Strings("Required - %s", row.file)
+          or Strings("Optional - %s", row.file)))
+    Kit.text("micro", Kit.ellipsize("micro", state, textW), innerX, stateY,
+      row.present and PAL.green or (row.required and PAL.yellow or PAL.muted))
+    btn(imp, actionX, cy + (rowH - m.btnH) / 2, actionW, m.btnH,
+      "req-pick-" .. mod.id .. "-" .. importId,
+      row.present and Strings("Replace") or Strings("Choose file"), {
+        kind = row.present and "ghost" or "accent", font = "small",
+        action = function() imp:chooseRequiredImport(mod.id, importId) end })
+    if row.present then
+      local deleteId = mod.id .. ":" .. importId
+      local armed = deleteArmed(imp, "required-import", deleteId, nil)
+      btn(imp, actionX + actionW + math.floor(6 * m.s),
+        cy + (rowH - m.btnH) / 2, removeW, m.btnH,
+        "req-remove-" .. mod.id .. "-" .. row.id, DELETE_LABEL(armed), {
+          kind = "danger", font = "small", keepArm = true,
+          action = function()
+            imp:pressDelete("required-import", deleteId, nil, function()
+              imp:_removeRequiredImport(mod.id, importId)
+            end)
+          end })
+    end
+    cy = cy + rowH + gap
+  end
+  if pagerH > 0 then
+    local newPage = Kit.pager(px + pad, cy, pw - 2 * pad, bounded,
+      #imports, perPage, pageKey)
+    setPage(imp, pageKey, newPage)
+    cy = cy + pagerH + gap
+  end
+  btn(imp, px + pad, cy, pw - 2 * pad, m.btnH, "req-close", Strings("Close"), {
+    font = "small", action = function() imp._modImports = nil end })
+end
+
 -- Per-mod popup for FIND MODS: the row is a plain click, and Install /
 -- Details / Source live here instead of crowding every row.
 local function buildFindEntryModal(imp, m)
@@ -3377,7 +3497,8 @@ local function modalUp(imp)
     or imp._indexPrompt or imp._modConfirm or imp._modReleaseNotes
     or imp._appPatchNotes
     or imp._findDetails or imp._modVersions or imp._modDepResolver or imp._sortPopup
-    or imp._filterPopup or imp._modScopePopup or imp._indexManage or imp._modActions
+    or imp._filterPopup or imp._modScopePopup or imp._indexManage
+    or imp._modActions or imp._modImports
     or imp._modHeaderActionsPopup or imp._profilesPopup or imp._singleProfileActions or imp._profileSavePrompt
     or imp._profileRenamePrompt or imp._findEntry or imp._gameManage) ~= nil
 end
@@ -3509,6 +3630,7 @@ local function buildModals(imp, m)
   end
   if imp._modVersions then buildVersionsModal(imp, m) return true end
   if imp._modDepResolver then buildDepResolverModal(imp, m) return true end
+  if imp._modImports then buildRequiredImportsModal(imp, m) return true end
   -- The lighter popups come after the deep ones on purpose: opening
   -- Versions or Details from inside an actions popup draws the deeper modal
   -- while the popup's own state stays set, so closing the deep one drops
diff --git a/src/import/RomImporter.lua b/src/import/RomImporter.lua
index 4666f226..1b178af4 100644
--- a/src/import/RomImporter.lua
+++ b/src/import/RomImporter.lua
@@ -344,6 +344,14 @@ local function readExternalPath(path)
   return data
 end
 
+local function externalFileSize(path)
+  local file = io.open(path, "rb")
+  if not file then return nil end
+  local size = file:seek("end")
+  file:close()
+  return size
+end
+
 local function readDroppedFile(file)
   local ok, openError = file:open("r")
   if not ok then return nil, openError end
@@ -981,6 +989,25 @@ local function findPendingSav(preferAny, skip)
   return nil
 end
 
+local function pickerHasKind(kind)
+  local fn = love.system.pickFileKinds
+  if type(fn) ~= "function" then return false end
+  local ok, kinds = pcall(fn)
+  if not ok or type(kinds) ~= "string" then return false end
+  for token in kinds:gmatch("[^,%s]+") do
+    if token == kind then return true end
+  end
+  return false
+end
+
+local function findPendingRequiredImport()
+  local names = { "picked_required_import.bin", "picked_stadium.z64" }
+  for _, name in ipairs(names) do
+    if love.filesystem.getInfo(name, "file") then return name end
+  end
+  return nil
+end
+
 -- Retire an Android pick once it has been through the installer / importer,
 -- whether or not it worked: a pick left on disk wins the scans above forever,
 -- so the next tap re-runs the same failing file and the picker never reopens
@@ -1112,6 +1139,39 @@ local function chooseSav()
   return nil
 end
 
+-- Generic user-supplied dependency picker. Keep the native prompt entirely
+-- engine-owned: manifest labels are untrusted and must never enter shell
+-- command templates. The LÖVE modal already shows the specific import name.
+local function chooseRequiredFile()
+  local prompt = shellSafe(Strings("Choose required mod file"))
+  local platform = love.system.getOS()
+  if platform == "OS X" then
+    return commandOutput(
+      ([[osascript -e 'POSIX path of (choose file with prompt "%s")' 2>/dev/null]])
+        :format(prompt))
+  elseif platform == "Windows" then
+    local script = table.concat({
+      "Add-Type -AssemblyName System.Windows.Forms;",
+      "$d=New-Object System.Windows.Forms.OpenFileDialog;",
+      "$d.Title='" .. prompt .. "';",
+      "$d.Filter='All files (*.*)|*.*';",
+      "if($d.ShowDialog() -eq 'OK'){",
+      "$t=Join-Path $env:TEMP 'pokeport_required_import.bin';",
+      "Copy-Item -LiteralPath $d.FileName -Destination $t -Force;",
+      "[Console]::OutputEncoding=[Text.Encoding]::UTF8;",
+      "[Console]::Write($t)}",
+    })
+    return commandOutput(
+      'powershell -NoProfile -STA -Command "' .. script .. '"')
+  elseif platform == "Linux" then
+    local path = commandOutput(
+      ([[zenity --file-selection --title="%s" 2>/dev/null]]):format(prompt))
+    if path then return path end
+    return commandOutput([[kdialog --getopenfilename "$HOME" 2>/dev/null]])
+  end
+  return nil
+end
+
 -- The self-updater only surfaces on the real distributed build: a fused,
 -- interactive launcher with no scripted-run override.  A dev / source checkout
 -- (unfused, where Boot.run already no-ops) or an autopilot / driver /
@@ -1230,7 +1290,9 @@ function RomImporter.new(onComplete, opts)
     -- (refreshed lazily on first draw and after any toggle/install/delete);
     -- modScroll is the current paged list's inner scroll offset (px, clamped
     -- in draw); modNotice is the last install/delete result { ok, text }.
-    mods = nil, modScroll = 0, modNotice = nil,
+    -- requiredImportNotice stays inside the imported-files modal so validation
+    -- failures are visible beside the file picker that caused them.
+    mods = nil, modScroll = 0, modNotice = nil, requiredImportNotice = nil,
     -- Which game the MODS panel is answering for (a GameVersion id, nil =
     -- every game).  Rows resolve their enable-state and their "runs here"
     -- verdict against it (src/mods/ModTargets.lua).
@@ -1420,7 +1482,13 @@ function RomImporter:focus(f)
     local text = "Could not read the picked file. Reopen the picker and choose "
       .. "it with the Files (Documents) app, or copy it into: "
       .. love.filesystem.getSaveDirectory()
-    if pickError:find("picked_mod", 1, true) then
+    if pickError:find("picked_required_import", 1, true)
+        or pickError:find("picked_stadium", 1, true) then
+      self.modNotice = { ok = false, text = text }
+      self.pickerPendingKind = nil
+      self.pickerPendingModId = nil
+      self.pickerPendingImportId = nil
+    elseif pickError:find("picked_mod", 1, true) then
       self.modNotice = { ok = false, text = text }
     elseif pickError:find("picked_save", 1, true) then
       local version = self.androidPendingVersion or self:_savedropTarget()
@@ -1431,6 +1499,20 @@ function RomImporter:focus(f)
     end
     return
   end
+  local requiredName = findPendingRequiredImport()
+  if requiredName then
+    local modId, importId = self.pickerPendingModId, self.pickerPendingImportId
+    self.pickerPendingKind = nil
+    self.pickerPendingModId, self.pickerPendingImportId = nil, nil
+    local imported = modId and importId
+      and self:_importRequiredSource(modId, importId, requiredName)
+    consumePick(self, requiredName, requiredName, imported)
+    if not modId or not importId then
+      self.modNotice = { ok = false,
+        text = "A picked dependency file had no pending mod request and was discarded." }
+    end
+    return
+  end
   local modName = findPendingMod(false, self.pickSkip)
   if modName then
     self:_installMod(modName)
@@ -1738,6 +1820,152 @@ function RomImporter:chooseMod()
   if path then self:_installMod(path) end
 end
 
+local function requiredManifest(self, modId)
+  for _, row in ipairs(self.mods or {}) do
+    if row.id == modId then return row.manifest, row end
+  end
+  return nil
+end
+
+local function requiredSpec(manifest, importId)
+  for _, candidate in ipairs(require("src.mods.RequiredImports").specs(manifest)) do
+    if candidate.id == importId then return candidate end
+  end
+  return nil
+end
+
+local function requiredImportNotice(self, modId, importId, text)
+  self.requiredImportNotice = {
+    modId = modId,
+    importId = importId,
+    text = tostring(text),
+  }
+end
+
+function RomImporter:_importRequiredData(modId, importId, data)
+  local manifest = requiredManifest(self, modId)
+  if not manifest then
+    self.modNotice = { ok = false, text = "Required import failed: mod not found." }
+    return nil
+  end
+  local ok, result = require("src.mods.RequiredImports")
+    .importData(manifest, importId, data)
+  if ok then
+    self.requiredImportNotice = nil
+    self.modNotice = { ok = true, text = "Imported " .. tostring(importId)
+      .. " for " .. tostring(manifest.name or manifest.id) .. "." }
+    self:_refreshMods()
+    return true
+  end
+  -- Keep validation feedback on the imported-files page.  A general Mods-page
+  -- notice is hidden by this modal and made MD5 failures especially easy to miss.
+  requiredImportNotice(self, modId, importId, result)
+  self.modNotice = nil
+  return nil
+end
+
+function RomImporter:_importRequiredSource(modId, importId, source)
+  local manifest = requiredManifest(self, modId)
+  local spec = manifest and requiredSpec(manifest, importId)
+  if not spec then
+    requiredImportNotice(self, modId, importId, "Import declaration was not found.")
+    self.modNotice = nil
+    return nil
+  end
+  local info = love.filesystem.getInfo(source, "file")
+  local size = info and info.size or externalFileSize(source)
+  local sizeErr = require("src.mods.RequiredImports").sizeError(spec, size, false)
+  if sizeErr then
+    requiredImportNotice(self, modId, importId, sizeErr)
+    self.modNotice = nil
+    return nil
+  end
+  local data = love.filesystem.read(source)
+  if not data then data = readExternalPath(source) end
+  if not data then
+    requiredImportNotice(self, modId, importId, "Could not read the selected file.")
+    self.modNotice = nil
+    return nil
+  end
+  return self:_importRequiredData(modId, importId, data)
+end
+
+function RomImporter:_removeRequiredImport(modId, importId)
+  local manifest = requiredManifest(self, modId)
+  if not manifest then return end
+  local ok, err = require("src.mods.RequiredImports").remove(manifest, importId)
+  if ok then
+    self.requiredImportNotice = nil
+    self.modNotice = { ok = true, text = "Deleted " .. tostring(importId) .. "." }
+    self:_refreshMods()
+  else
+    requiredImportNotice(self, modId, importId, err)
+    self.modNotice = nil
+  end
+end
+
+-- Select and validate one manifest-declared file.  NX has no host picker, so
+-- its equivalent is an engine-owned imports/baseroms inbox that can be filled
+-- over MTP; every other native/mobile picker lands on the same validation path.
+function RomImporter:chooseRequiredImport(modId, importId)
+  if self.workState == "working" then return end
+  local manifest = requiredManifest(self, modId)
+  if not manifest then return end
+  local spec = requiredSpec(manifest, importId)
+  if not spec then return end
+
+  if self.isNX then
+    local inbox = "imports/baseroms"
+    love.filesystem.createDirectory(inbox)
+    local lastError
+    for _, name in ipairs(love.filesystem.getDirectoryItems(inbox) or {}) do
+      if name:sub(1, 1) ~= "." then
+        local path = inbox .. "/" .. name
+        local info = love.filesystem.getInfo(path, "file")
+        local sizeErr = info and require("src.mods.RequiredImports")
+          .sizeError(spec, info.size, false)
+        local data = not sizeErr and love.filesystem.read(path) or nil
+        if data and self:_importRequiredData(modId, importId, data) then return end
+        if sizeErr then lastError = sizeErr
+        elseif self.requiredImportNotice
+            and self.requiredImportNotice.modId == modId
+            and self.requiredImportNotice.importId == importId then
+          lastError = self.requiredImportNotice.text
+        end
+      end
+    end
+    requiredImportNotice(self, modId, importId, lastError
+      or "No matching file in imports/baseroms/. Copy it there over MTP, then try again.")
+    self.modNotice = nil
+    return
+  end
+  if self.nativePicker then
+    if self.mobileFileBridge and not pickerHasKind("required_import") then
+      requiredImportNotice(self, modId, importId,
+        "This app build cannot pick required mod files yet. Update the app and try again.")
+      self.modNotice = nil
+      return
+    end
+    self.pickerPendingKind = "required_import"
+    self.pickerPendingModId = modId
+    self.pickerPendingImportId = importId
+    if not pickFile("required_import") then
+      self.pickerPendingKind = nil
+      self.pickerPendingModId = nil
+      self.pickerPendingImportId = nil
+      requiredImportNotice(self, modId, importId, "Could not open the file picker.")
+      self.modNotice = nil
+    elseif self.android then
+      self.pickPending = true
+      self.pickTimer = 0
+    end
+    return
+  end
+
+  local path = chooseRequiredFile()
+  if path then self:_importRequiredSource(modId, importId, path) end
+end
+
 -- Which game a dropped .sav imports into: a .sav has no version signature of
 -- its own, so it lands on the active game tab.  When a non-game tab (mods) is
 -- showing, default to red -- the always-present first game -- rather than
@@ -2045,7 +2273,8 @@ function RomImporter:_pollPickedFiles(dt)
   if not found then
     for _, name in ipairs(love.filesystem.getDirectoryItems("")) do
       local n = name:lower()
-      if n:match("%.gbc?$") or n == "picked_mod.zip" or n == "picked_save.sav" then
+      if n:match("%.gbc?$") or n == "picked_mod.zip" or n == "picked_save.sav"
+          or n == "picked_required_import.bin" or n == "picked_stadium.z64" then
         found = true
         break
       end
@@ -2174,7 +2403,12 @@ function RomImporter:update(dt)
       local version = self.pickerPendingVersion
       self.pickerPendingKind = nil
       self.pickerPendingVersion = nil
-      if kind == "mod" then
+      if kind == "required_import" then
+        local modId, importId = self.pickerPendingModId, self.pickerPendingImportId
+        self.pickerPendingModId, self.pickerPendingImportId = nil, nil
+        if modId and importId then self:_importRequiredSource(modId, importId, path) end
+        if Platform.isUWP() then os.remove(path) end
+      elseif kind == "mod" then
         self:_installMod(path)
         if Platform.isUWP() and self.modNotice and self.modNotice.ok then
           os.remove(path)
@@ -2196,7 +2430,10 @@ function RomImporter:update(dt)
         local version = self.pickerPendingVersion or self:_savedropTarget()
         self.pickerPendingKind = nil
         self.pickerPendingVersion = nil
-        if kind == "mod" then
+        if kind == "required_import" then
+          self.modNotice = { ok = false, text = errorText }
+          self.pickerPendingModId, self.pickerPendingImportId = nil, nil
+        elseif kind == "mod" then
           self.modNotice = { ok = false, text = errorText }
         elseif kind == "sav" then
           self.saveNotice[version] = { ok = false, text = errorText }
diff --git a/src/mods/LauncherMods.lua b/src/mods/LauncherMods.lua
index 4f7f2ba8..87e51acb 100644
--- a/src/mods/LauncherMods.lua
+++ b/src/mods/LauncherMods.lua
@@ -38,6 +38,7 @@ local Version = require("src.core.Version")
 local SaveData = require("src.core.SaveData")
 local GameVersion = require("src.core.GameVersion")
 local CacheFs = require("src.import.CacheFs")
+local RequiredImports = require("src.mods.RequiredImports")
 
 local LauncherMods = {}
 
@@ -459,13 +460,38 @@ function LauncherMods.list(version)
   local ok, result = pcall(function()
     local options = SaveData.loadOptions()
     local manifests = discover()
+    -- Imports are private player grants. Never scan or copy another mod's
+    -- baseroms: a matching public digest is not permission to share the file.
+    local importState = {}
+    for _, manifest in ipairs(manifests) do
+      local rows, missing, missingOptional = RequiredImports.inspect(manifest)
+      importState[manifest.id] = { rows = rows, missing = missing,
+        missingOptional = missingOptional }
+    end
     -- The first build containing game-specific switches turns the old shared
     -- state into one explicit answer per installed mod and game.  Saving here
     -- means users who only visit the launcher still receive the migration.
     if SaveData.migrateModEnablement(options, manifests) then
       SaveData.saveOptions(options)
     end
-    return LauncherMods.deriveList(manifests, options, version)
+    local rows = LauncherMods.deriveList(manifests, options, version)
+    for _, row in ipairs(rows) do
+      local state = importState[row.id]
+        or { rows = {}, missing = 0, missingOptional = 0 }
+      local imports, missing = state.rows, state.missing
+      row.requiredImports, row.missingRequiredImports = imports, missing
+      row.imports = imports
+      row.missingOptionalImports = state.missingOptional or 0
+      if missing > 0 and row.status == "ok" then
+        row.status = "needs_import"
+        local first
+        for _, import in ipairs(imports) do
+          if not import.present then first = import break end
+        end
+        row.statusDetail = "Needs import: " .. (first and first.name or "required file")
+      end
+    end
+    return rows
   end)
   if not ok then
     -- a single bad options/mod file must not blank the launcher
@@ -677,6 +703,26 @@ local function copyTree(src, dst)
   return true
 end
 
+-- User-supplied baseroms are install state, not package content.  Snapshot
+-- them before replacing a mod tree so an update cannot make the player select
+-- the same cartridge again (or destroy their only reusable copy if the new
+-- archive later fails to copy).
+local function snapshotTree(path, into, relative)
+  local fs = love.filesystem
+  into, relative = into or {}, relative or ""
+  local info = fs.getInfo(path)
+  if not info then return into end
+  if info.type == "directory" then
+    for _, name in ipairs(fs.getDirectoryItems(path) or {}) do
+      local rel = relative == "" and name or (relative .. "/" .. name)
+      snapshotTree(path .. "/" .. name, into, rel)
+    end
+  elseif relative ~= "" and into[relative] == nil then
+    into[relative] = fs.read(path)
+  end
+  return into
+end
+
 -- Delete an installed mod subtree.  Enumeration stays on love.filesystem (the
 -- portable game folder is on its read path), but the deletes go through
 -- CacheFs so a portable install's real files actually go away instead of
@@ -919,14 +965,28 @@ function LauncherMods._installZipInner(source, opts)
     return nil, ("zip is for '%s', expected '%s'")
       :format(manifest.id, opts.expectId)
   end
+  local packagedBaseroms = root .. "/baseroms"
+  if fs.getInfo(packagedBaseroms, "directory")
+      and #(fs.getDirectoryItems(packagedBaseroms) or {}) > 0 then
+    cleanup()
+    return nil, "mod archives must not include user-supplied baseroms/ files"
+  end
 
   local dest = "mods/" .. manifest.id
+  local baseromRecovery = "imports/baseroms-recovery/" .. manifest.id
   local existing, installedSomewhere = sameIdTrees(fs, manifest.id)
   if installedSomewhere and not opts.replace then
     cleanup()
     return nil, "a mod named '" .. manifest.id .. "' is already installed"
   end
+  local preservedBaseroms = {}
+  -- A previous failed update may have staged the user's files outside mods/ so
+  -- discovery cannot mistake recovery debris for an installed mod.
+  snapshotTree(baseromRecovery, preservedBaseroms)
   if #existing > 0 then
+    for _, path in ipairs(existing) do
+      snapshotTree(path .. "/baseroms", preservedBaseroms)
+    end
     -- drop every old tree before copy -- mods/<id> and any same-id folder
     -- under another name, or the survivor keeps winning discover()'s
     -- first-id-wins race after the "successful" update (#801).  A tree with
@@ -950,6 +1010,28 @@ function LauncherMods._installZipInner(source, opts)
   CacheFs.prefix = ""
   local copied, copyErr = copyTree(root, dest)
   if not copied then removeTree(dest) end
+  local preserveErr
+  for rel, bytes in pairs(preservedBaseroms) do
+    if bytes ~= nil then
+      local restored, restoreErr = CacheFs.write(dest .. "/baseroms/" .. rel, bytes)
+      if not restored and not preserveErr then
+        preserveErr = "could not preserve baseroms/" .. rel .. ": "
+          .. tostring(restoreErr)
+      end
+    end
+  end
+  if preserveErr then
+    -- Do not report a successful update that discarded user-owned input, and
+    -- do not leave a manifest-less baseroms tree that resembles an install.
+    removeTree(dest)
+    removeTree(baseromRecovery)
+    for rel, bytes in pairs(preservedBaseroms) do
+      if bytes ~= nil then CacheFs.write(baseromRecovery .. "/" .. rel, bytes) end
+    end
+    copied, copyErr = nil, preserveErr
+  elseif copied then
+    removeTree(baseromRecovery)
+  end
   CacheFs.prefix = savedPrefix
   if not copied then
     cleanup()
diff --git a/src/mods/Loader.lua b/src/mods/Loader.lua
index 8854b9bb..1a46dbf9 100644
--- a/src/mods/Loader.lua
+++ b/src/mods/Loader.lua
@@ -4,6 +4,7 @@ local SaveData = require("src.core.SaveData")
 local Data = require("src.core.Data")
 local GameVersion = require("src.core.GameVersion")
 local Version = require("src.core.Version")
+local RequiredImports = require("src.mods.RequiredImports")
 local Assets = require("src.render.Assets")
 local ModUI = require("src.ui.ModUI")
 local DateTime = require("src.core.DateTime")
@@ -565,7 +566,24 @@ function Loader:_validate()
     elseif manifest.assets_transforms
         and not self:_exists(mod.path .. "/" .. manifest.assets_transforms) then
       reason = "assets_transforms file missing: " .. manifest.assets_transforms
-    elseif manifest.game_version and not devEngine() then
+    end
+    if not reason and #(manifest.required_imports or {}) > 0 then
+      for _, import in ipairs(manifest.required_imports) do
+        local path = mod.path .. "/baseroms/" .. import.file
+        if not self:_exists(path) then
+          reason = "required import missing: " .. import.name
+          break
+        end
+        local valid, importErr = RequiredImports.validateStored(
+          manifest, import, self.fs)
+        if not valid then
+          reason = "required import invalid: " .. import.name
+            .. " (" .. tostring(importErr) .. ")"
+          break
+        end
+      end
+    end
+    if not reason and manifest.game_version and not devEngine() then
       local ok, err = Semver.satisfies(Version.engine, manifest.game_version)
       if not ok then
         reason = ("needs game version %s, engine is %s")
diff --git a/src/mods/Manifest.lua b/src/mods/Manifest.lua
index 95383cde..1fef0295 100644
--- a/src/mods/Manifest.lua
+++ b/src/mods/Manifest.lua
@@ -132,13 +132,97 @@ local function mergeConflictLists(conflicts, incompatible)
   return out
 end
 
+local scrubUtf8 -- shared by required-import labels and top-level strings
+
+-- User-supplied files a mod needs beside its own source.  The launcher owns
+-- the picker and the copy; the mod only reads the resulting
+-- <mod>/baseroms/<file> through its existing scoped mod:read surface.  MD5 is
+-- deliberately the manifest vocabulary here: ROM preservation databases and
+-- the mods consuming these files commonly identify dumps by MD5, and the
+-- digest is an identity check rather than a security boundary.
+local function parseImports(value, field, required)
+  field = field or "required_imports"
+  local out, ids, files = {}, {}, {}
+  for _, entry in ipairs(array(value)) do
+    assert(type(entry) == "table", field .. " entries must be objects")
+    local id = entry.id
+    assert(type(id) == "string" and id:match("^[%w_%-]+$"),
+      field .. " id must contain only letters, numbers, _ or -")
+    assert(not ids[id], "duplicate " .. field .. " id: " .. id)
+    ids[id] = true
+
+    local file = entry.file
+    assert(type(file) == "string" and file ~= "",
+      field .. " file is required")
+    file = SafePath.require(file, field .. " file")
+    assert(not file:find("/", 1, true),
+      field .. " file must be a filename inside baseroms")
+    assert(file:sub(1, 1) ~= ".",
+      field .. " file must not use a hidden metadata filename")
+    assert(not files[file], "duplicate " .. field .. " file: " .. file)
+    files[file] = true
+
+    local hashes = entry.md5
+    if type(hashes) == "string" then hashes = { hashes } end
+    assert(type(hashes) == "table" and #hashes > 0,
+      field .. " md5 must be a hash or non-empty array")
+    local accepted, seen = {}, {}
+    for _, digest in ipairs(hashes) do
+      assert(type(digest) == "string" and digest:match("^[%x]+$")
+          and #digest == 32, field .. " md5 values must be 32 hex characters")
+      digest = digest:lower()
+      if not seen[digest] then
+        seen[digest] = true
+        accepted[#accepted + 1] = digest
+      end
+    end
+
+    local format = entry.format or "raw"
+    assert(format == "raw" or format == "n64",
+      field .. " format must be raw or n64")
+    local name = entry.name or id
+    assert(type(name) == "string" and name ~= "",
+      field .. " name must be a non-empty string")
+    local description = entry.description or entry.hint
+    if description ~= nil then
+      assert(type(description) == "string" and description ~= "",
+        field .. " description must be a non-empty string")
+    end
+    local size = entry.size
+    local maxSize = entry.max_size
+    local function validateSize(value, label)
+      if value == nil then return end
+      assert(type(value) == "number" and value > 0 and value % 1 == 0,
+        field .. " " .. label .. " must be a positive integer")
+      assert(value <= 128 * 1024 * 1024,
+        field .. " " .. label .. " exceeds the 128 MiB hard limit")
+    end
+    validateSize(size, "size")
+    validateSize(maxSize, "max_size")
+    assert(not (size and maxSize) or size <= maxSize,
+      field .. " size must not exceed max_size")
+    out[#out + 1] = {
+      id = id,
+      name = scrubUtf8(name),
+      description = scrubUtf8(description),
+      file = file,
+      md5 = accepted,
+      format = format,
+      size = size,
+      max_size = maxSize,
+      required = required ~= false,
+    }
+  end
+  return out
+end
+
 -- Drop bytes that are not valid UTF-8 (malformed sequences, overlongs,
 -- surrogates, > U+10FFFF) and a leading BOM.  LÖVE's text renderer raises
 -- "Invalid UTF-8" from love.graphics.print/printf, so any manifest string a
 -- panel may draw must be scrubbed here -- the one place every mod manifest
 -- passes through -- or a single mangled description crashes the whole MODS
 -- panel instead of misrendering one card.
-local function scrubUtf8(s)
+scrubUtf8 = function(s)
   if type(s) ~= "string" then return s end
   s = s:gsub("^\239\187\191", "")
   local out, i, n = {}, 1, #s
@@ -290,6 +374,19 @@ function Manifest.validate(raw, path)
 
   local conflicts = mergeConflictLists(raw.conflicts, raw.incompatible)
 
+  local requiredImports = parseImports(raw.required_imports,
+    "required_imports", true)
+  local optionalImports = parseImports(raw.optional_imports,
+    "optional_imports", false)
+  local importIds, importFiles = {}, {}
+  for _, list in ipairs({ requiredImports, optionalImports }) do
+    for _, import in ipairs(list) do
+      assert(not importIds[import.id], "duplicate import id: " .. import.id)
+      assert(not importFiles[import.file], "duplicate import file: " .. import.file)
+      importIds[import.id], importFiles[import.file] = true, true
+    end
+  end
+
   return {
     id = raw.id,
     name = raw.name,
@@ -318,6 +415,8 @@ function Manifest.validate(raw, path)
     permissionSet = permissionSet,
     options_schema = optionalFile(raw.options_schema, "options_schema"),
     assets_transforms = optionalFile(raw.assets_transforms, "assets_transforms"),
+    required_imports = requiredImports,
+    optional_imports = optionalImports,
     -- an env var name, not a path, so it keeps the plain string check
     force_enable_env = optionalString(raw.force_enable_env, "force_enable_env"),
     path = path,
diff --git a/src/mods/RequiredImports.lua b/src/mods/RequiredImports.lua
new file mode 100644
index 00000000..167c263f
--- /dev/null
+++ b/src/mods/RequiredImports.lua
@@ -0,0 +1,295 @@
+-- Engine-owned import handling for files declared by a mod's required or
+-- optional import arrays. Mods never receive host paths or broader
+-- filesystem access: accepted bytes are copied into their own
+-- mods/<id>/baseroms/ tree, where the existing mod:read sandbox can see them.
+
+local CacheFs = require("src.import.CacheFs")
+
+local RequiredImports = {}
+
+local function allSpecs(manifest)
+  local out = {}
+  for _, spec in ipairs((manifest and manifest.required_imports) or {}) do
+    out[#out + 1] = spec
+  end
+  for _, spec in ipairs((manifest and manifest.optional_imports) or {}) do
+    out[#out + 1] = spec
+  end
+  return out
+end
+
+local function isRequired(spec)
+  return spec.required ~= false
+end
+
+RequiredImports.specs = allSpecs
+RequiredImports.MAX_BYTES = 128 * 1024 * 1024
+
+local function sizeLabel(bytes)
+  return ("%.1f MiB"):format(bytes / (1024 * 1024))
+end
+
+-- Check size before a caller reads an external or stored file into one large
+-- Lua string. N64 sources may carry a 512-byte copier header, while stored
+-- files are always canonical and therefore must match the declared size.
+function RequiredImports.sizeError(spec, size, stored)
+  if type(size) ~= "number" then return nil end
+  if size > RequiredImports.MAX_BYTES then
+    return ("file is too large (%s; hard limit is %s)")
+      :format(sizeLabel(size), sizeLabel(RequiredImports.MAX_BYTES))
+  end
+  local headerAllowance = not stored and spec and spec.format == "n64" and 512 or 0
+  if spec and spec.size then
+    if size ~= spec.size and size ~= spec.size + headerAllowance then
+      return ("wrong file size (expected %d bytes%s, got %d)")
+        :format(spec.size, headerAllowance > 0 and " or a 512-byte header" or "", size)
+    end
+  end
+  if spec and spec.max_size and size > spec.max_size + headerAllowance then
+    return ("file is too large for this import (maximum %d bytes, got %d)")
+      :format(spec.max_size, size)
+  end
+  return nil
+end
+
+local N64_MAGIC = {
+  ["\128\55\18\64"] = "z64", -- big endian / canonical
+  ["\55\128\64\18"] = "v64", -- byte-swapped
+  ["\64\18\55\128"] = "n64", -- little endian words
+}
+
+local function n64KindAt(data, offset)
+  return N64_MAGIC[data:sub(offset, offset + 3)]
+end
+
+-- Return canonical big-endian N64 bytes.  A 512-byte copier header is
+-- recognized only when valid N64 magic follows it, so arbitrary data is never
+-- shortened just because its size happens to line up.
+function RequiredImports.normalizeN64(data)
+  if type(data) ~= "string" then return nil, "selected file could not be read" end
+  local offset, kind = 1, n64KindAt(data, 1)
+  if not kind then
+    kind = n64KindAt(data, 513)
+    if kind then offset = 513 end
+  end
+  if not kind then
+    return nil, "expected an N64 ROM (.z64/.v64/.n64); file signature was not recognized"
+  end
+  data = data:sub(offset)
+  if kind == "z64" then return data end
+
+  if kind == "v64" then
+    if #data % 2 ~= 0 then return nil, "byte-swapped N64 ROM has an odd size" end
+    return (data:gsub("(.)(.)", "%2%1"))
+  else
+    if #data % 4 ~= 0 then return nil, "little-endian N64 ROM size is not word aligned" end
+    return (data:gsub("(.)(.)(.)(.)", "%4%3%2%1"))
+  end
+end
+
+function RequiredImports.normalize(spec, data)
+  if spec and spec.format == "n64" then
+    return RequiredImports.normalizeN64(data)
+  end
+  if type(data) ~= "string" then return nil, "selected file could not be read" end
+  return data
+end
+
+local function hexDigest(data, hashFn)
+  if hashFn then return hashFn(data):lower() end
+  if not (love and love.data and love.data.hash and love.data.encode) then
+    return nil, "MD5 support is unavailable in this build"
+  end
+  local digest = love.data.hash("md5", data)
+  if type(digest) == "userdata" and digest.getString then
+    digest = digest:getString()
+  end
+  return love.data.encode("string", "hex", digest):lower()
+end
+
+local function accepts(spec, digest)
+  for _, wanted in ipairs((spec and spec.md5) or {}) do
+    if wanted == digest then return true end
+  end
+  return false
+end
+
+function RequiredImports.path(manifest, spec)
+  return manifest.path .. "/baseroms/" .. spec.file
+end
+
+local function removedMarker(manifest, spec)
+  return manifest.path .. "/baseroms/.required-import-" .. spec.id .. ".removed"
+end
+
+local function receiptPath(manifest, spec)
+  return manifest.path .. "/baseroms/.required-import-" .. spec.id .. ".validated"
+end
+
+RequiredImports.receiptPath = receiptPath
+
+local function parseReceipt(raw)
+  if type(raw) ~= "string" then return nil end
+  local digest, size, modtime = raw:match("^v1\n([%x]+)\n(%d+)\n([^\n]+)\n?$")
+  if not digest then return nil end
+  return digest:lower(), tonumber(size), tonumber(modtime)
+end
+
+local function cachedDigest(manifest, spec, fs, info)
+  -- A size alone cannot detect a same-length replacement. Require modtime as
+  -- well; filesystems that do not expose it simply take the safe hash path.
+  if not (fs and fs.read and info and info.size and info.modtime) then return nil end
+  local digest, size, modtime = parseReceipt(fs.read(receiptPath(manifest, spec)))
+  if digest and size == info.size and modtime == info.modtime
+      and accepts(spec, digest) then
+    return digest
+  end
+  return nil
+end
+
+local function writeReceipt(manifest, spec, digest, info, fs)
+  if not (digest and info and info.size and info.modtime) then return end
+  local path = receiptPath(manifest, spec)
+  local body = ("v1\n%s\n%d\n%s\n")
+    :format(digest, info.size, tostring(info.modtime))
+  if love and fs == love.filesystem then
+    local savedPrefix = CacheFs.prefix
+    CacheFs.prefix = ""
+    CacheFs.write(path, body)
+    CacheFs.prefix = savedPrefix
+  elseif fs and fs.write then
+    fs.write(path, body)
+  end
+end
+
+local function removeReceipt(manifest, spec, fs)
+  local path = receiptPath(manifest, spec)
+  if love and fs == love.filesystem then
+    local savedPrefix = CacheFs.prefix
+    CacheFs.prefix = ""
+    CacheFs.remove(path)
+    CacheFs.prefix = savedPrefix
+  elseif fs and fs.remove then
+    fs.remove(path)
+  end
+end
+
+-- Validate bytes against a declaration.  The returned data is canonicalized
+-- (notably for N64 byte order/header variants) and is what must be stored.
+function RequiredImports.validateData(spec, data, hashFn)
+  local sourceSizeErr = type(data) == "string"
+    and RequiredImports.sizeError(spec, #data, false)
+  if sourceSizeErr then return nil, sourceSizeErr end
+  local normalized, normalizeErr = RequiredImports.normalize(spec, data)
+  if not normalized then return nil, normalizeErr end
+  local storedSizeErr = RequiredImports.sizeError(spec, #normalized, true)
+  if storedSizeErr then return nil, storedSizeErr end
+  local digest, hashErr = hexDigest(normalized, hashFn)
+  if not digest then return nil, hashErr end
+  if not accepts(spec, digest) then
+    return nil, ("MD5 mismatch (got %s)"):format(digest)
+  end
+  return normalized, digest
+end
+
+-- Validate one installed import without reading it when the engine-authored
+-- receipt still matches the file's size and modification time.
+function RequiredImports.validateStored(manifest, spec, fs, hashFn)
+  fs = fs or (love and love.filesystem)
+  if not (fs and fs.getInfo) then return nil, "filesystem is unavailable" end
+  local path = RequiredImports.path(manifest, spec)
+  local info = fs.getInfo(path, "file")
+  if not info then
+    removeReceipt(manifest, spec, fs)
+    return nil, "file is missing"
+  end
+  local sizeErr = RequiredImports.sizeError(spec, info.size, true)
+  if sizeErr then
+    removeReceipt(manifest, spec, fs)
+    return nil, sizeErr
+  end
+  local cached = cachedDigest(manifest, spec, fs, info)
+  if cached then return true, cached, true end
+  removeReceipt(manifest, spec, fs)
+  if not fs.read then return nil, "file could not be read" end
+  local data = fs.read(path)
+  local normalized, detail = RequiredImports.validateStoredData(spec, data, hashFn)
+  if not normalized then return nil, detail end
+  info = fs.getInfo(path, "file") or info
+  info.size = info.size or #data
+  writeReceipt(manifest, spec, detail, info, fs)
+  return true, detail, false
+end
+
+function RequiredImports.validateStoredData(spec, data, hashFn)
+  local normalized, detail = RequiredImports.validateData(spec, data, hashFn)
+  if not normalized then return nil, detail end
+  if normalized ~= data then
+    return nil, "stored N64 ROM is not canonical; choose the source file again"
+  end
+  return normalized, detail
+end
+
+function RequiredImports.inspect(manifest, fs, hashFn)
+  fs = fs or (love and love.filesystem)
+  local rows, missing, missingOptional = {}, 0, 0
+  for _, spec in ipairs(allSpecs(manifest)) do
+    local path = RequiredImports.path(manifest, spec)
+    local suppressed = fs and fs.getInfo
+      and fs.getInfo(removedMarker(manifest, spec), "file") ~= nil
+    local exists = fs and fs.getInfo and fs.getInfo(path, "file") ~= nil
+    local valid, detail = RequiredImports.validateStored(manifest, spec, fs, hashFn)
+    local row = { id = spec.id, name = spec.name, file = spec.file,
+      description = spec.description, format = spec.format, path = path,
+      present = valid == true, digest = valid and detail or nil,
+      error = exists and not valid and detail or nil,
+      suppressed = suppressed, required = isRequired(spec), spec = spec }
+    if not row.present then
+      if row.required then missing = missing + 1
+      else missingOptional = missingOptional + 1 end
+    end
+    rows[#rows + 1] = row
+  end
+  return rows, missing, missingOptional
+end
+
+function RequiredImports.importData(manifest, importId, data, opts)
+  opts = opts or {}
+  local spec
+  for _, candidate in ipairs(allSpecs(manifest)) do
+    if candidate.id == importId then spec = candidate break end
+  end
+  if not spec then return nil, "unknown required import: " .. tostring(importId) end
+  local normalized, digest = RequiredImports.validateData(spec, data, opts.hash)
+  if not normalized then return nil, digest end
+  local savedPrefix = CacheFs.prefix
+  CacheFs.prefix = ""
+  CacheFs.remove(receiptPath(manifest, spec))
+  local ok, err = CacheFs.write(RequiredImports.path(manifest, spec), normalized)
+  if ok then CacheFs.remove(removedMarker(manifest, spec)) end
+  if ok and love and love.filesystem and love.filesystem.getInfo then
+    local info = love.filesystem.getInfo(RequiredImports.path(manifest, spec), "file")
+    writeReceipt(manifest, spec, digest, info, love.filesystem)
+  end
+  CacheFs.prefix = savedPrefix
+  if not ok then return nil, "could not copy import: " .. tostring(err) end
+  return true, digest
+end
+
+function RequiredImports.remove(manifest, importId)
+  for _, spec in ipairs(allSpecs(manifest)) do
+    if spec.id == importId then
+      local savedPrefix = CacheFs.prefix
+      CacheFs.prefix = ""
+      CacheFs.remove(RequiredImports.path(manifest, spec))
+      CacheFs.remove(receiptPath(manifest, spec))
+      local marked, markErr = CacheFs.write(removedMarker(manifest, spec), "removed\n")
+      CacheFs.prefix = savedPrefix
+      if not marked then return nil, "could not remember removal: " .. tostring(markErr) end
+      return true
+    end
+  end
+  return nil, "unknown required import: " .. tostring(importId)
+end
+
+return RequiredImports
diff --git a/tests/launcher_mods_install_zip_test.lua b/tests/launcher_mods_install_zip_test.lua
index e7b117f9..2ef9dd51 100644
--- a/tests/launcher_mods_install_zip_test.lua
+++ b/tests/launcher_mods_install_zip_test.lua
@@ -17,6 +17,7 @@ local ARCHIVE = {
 local files, dirs, arch = {}, {}, {}
 local fileDataMounts, pathMounts, stagedTemps = 0, 0, {}
 local stagedEver = false
+local failWriteOnce
 
 local function resetFs()
   for k in pairs(files) do files[k] = nil end
@@ -25,6 +26,7 @@ local function resetFs()
   fileDataMounts, pathMounts = 0, 0
   stagedTemps = {}
   stagedEver = false
+  failWriteOnce = nil
 end
 
 local function dirChild(key, name)
@@ -45,6 +47,10 @@ end
 local vfs = {}
 
 function vfs.write(name, data)
+  if failWriteOnce == name then
+    failWriteOnce = nil
+    return nil, "simulated write failure"
+  end
   files[name] = data
   if name:match("^mod_import_") then
     stagedTemps[name] = true
@@ -171,6 +177,16 @@ eq(staged, 0, "FileData path leaves no staged temp zip")
 check(files["mods/" .. MOD_ID .. "/manifest.json"] ~= nil,
   "install wrote manifest into mods/")
 
+-- A third-party archive cannot bypass modkit's no-baseroms packaging gate.
+resetFs()
+ARCHIVE[MOD_ID .. "/baseroms/source.z64"] = "packaged rom"
+files["imports/mods/packaged-rom.zip"] = "PK\3\4packaged-rom"
+ok, err = LauncherMods.installZip("imports/mods/packaged-rom.zip")
+check(not ok, "an archive containing baseroms is rejected")
+check(tostring(err):find("must not include", 1, true),
+  "baseroms archive rejection explains the policy")
+ARCHIVE[MOD_ID .. "/baseroms/source.z64"] = nil
+
 -- Fallback: no newFileData → stage temp + path mount
 resetFs()
 vfs.newFileData = nil
@@ -205,6 +221,50 @@ check(files["mods/WildsOfKanto-1.5.0/manifest.json"] == nil,
 check(files["mods/" .. MOD_ID .. "/manifest.json"] ~= nil,
   "replace still lands in mods/<id>")
 
+-- User-selected baseroms belong to the installation, not the downloaded mod
+-- archive, and survive the same replacement path.
+resetFs()
+files["mods/OldFolder/manifest.json"] =
+  ('{"id":"%s","name":"Old Copy","version":"0.9.0","entry":"main.lua"}')
+    :format(MOD_ID)
+files["mods/OldFolder/main.lua"] = "return function() end\n"
+files["mods/OldFolder/baseroms/stadium2.z64"] = "user-owned-rom"
+files["imports/mods/update-with-rom.zip"] = "PK\3\4update"
+ok, err = LauncherMods.installZip("imports/mods/update-with-rom.zip",
+  { replace = true, expectId = MOD_ID })
+check(ok == true, "replace with a baserom succeeds (" .. tostring(err) .. ")")
+eq(files["mods/" .. MOD_ID .. "/baseroms/stadium2.z64"], "user-owned-rom",
+  "replace preserves user-owned baseroms under the canonical mod folder")
+check(files["mods/OldFolder/baseroms/stadium2.z64"] == nil,
+  "the shadow mod tree is still removed after preservation")
+
+-- A preservation write failure keeps recovery bytes outside mods/, where
+-- discovery cannot mistake a baseroms-only directory for an installed mod.
+resetFs()
+files["mods/OldFolder/manifest.json"] =
+  ('{"id":"%s","name":"Old Copy","version":"0.9.0","entry":"main.lua"}')
+    :format(MOD_ID)
+files["mods/OldFolder/main.lua"] = "return function() end\n"
+files["mods/OldFolder/baseroms/stadium2.z64"] = "user-owned-rom"
+files["imports/mods/preserve-fail.zip"] = "PK\3\4update"
+failWriteOnce = "mods/" .. MOD_ID .. "/baseroms/stadium2.z64"
+ok, err = LauncherMods.installZip("imports/mods/preserve-fail.zip",
+  { replace = true, expectId = MOD_ID })
+check(not ok, "preservation failure rejects the update")
+check(files["mods/" .. MOD_ID .. "/manifest.json"] == nil,
+  "preservation failure leaves no manifest-less tree under mods")
+eq(files["imports/baseroms-recovery/" .. MOD_ID .. "/stadium2.z64"],
+  "user-owned-rom", "preservation failure stages recovery outside mods")
+
+files["imports/mods/preserve-retry.zip"] = "PK\3\4update"
+ok, err = LauncherMods.installZip("imports/mods/preserve-retry.zip",
+  { replace = true, expectId = MOD_ID })
+check(ok == true, "retry restores staged baseroms (" .. tostring(err) .. ")")
+eq(files["mods/" .. MOD_ID .. "/baseroms/stadium2.z64"], "user-owned-rom",
+  "retry restores the recovered baserom into the installed mod")
+check(files["imports/baseroms-recovery/" .. MOD_ID .. "/stadium2.z64"] == nil,
+  "successful retry clears baserom recovery debris")
+
 -- #834: a manifest-less mods/<id> tree (interrupted copy debris) must not
 -- block a plain re-import as "already installed"
 resetFs()
diff --git a/tests/mod_required_imports_tests.lua b/tests/mod_required_imports_tests.lua
new file mode 100644
index 00000000..271465b5
--- /dev/null
+++ b/tests/mod_required_imports_tests.lua
@@ -0,0 +1,256 @@
+package.path = "./?.lua;./?/init.lua;" .. package.path
+love = love or require("tests.love_stub")
+
+local Manifest = require("src.mods.Manifest")
+local RequiredImports = require("src.mods.RequiredImports")
+local Loader = require("src.mods.Loader")
+local S = require("tests.harness").suite("required mod imports")
+local check, eq = S.check, S.eq
+
+local DIGEST = "0123456789abcdef0123456789abcdef"
+local function fakeHash(data)
+  return data:sub(1, 4) == "\128\55\18\64" and DIGEST
+    or "ffffffffffffffffffffffffffffffff"
+end
+
+local manifest = Manifest.validate({
+  id = "stadium_fx", name = "Stadium FX", version = "1.0.0", entry = "main.lua",
+  required_imports = {
+    { id = "stadium2", name = "Stadium 2", file = "stadium2.z64",
+      description = "USA dump", format = "n64", size = 8,
+      md5 = { DIGEST, DIGEST:upper() } },
+  },
+}, "mods/stadium_fx")
+
+eq(#manifest.required_imports, 1, "required import parses")
+eq(#manifest.required_imports[1].md5, 1, "accepted MD5 values normalize and dedupe")
+eq(manifest.required_imports[1].md5[1], DIGEST, "MD5 is lowercase")
+eq(manifest.required_imports[1].description, "USA dump",
+  "import description is preserved for the picker UI")
+eq(manifest.required_imports[1].size, 8, "exact import size parses")
+
+local optionalManifest = Manifest.validate({
+  id = "optional_fx", name = "Optional FX", version = "1.0.0", entry = "main.lua",
+  optional_imports = {
+    { id = "bonus", name = "Bonus ROM", file = "bonus.z64",
+      format = "n64", md5 = DIGEST },
+  },
+}, "mods/optional_fx")
+eq(#optionalManifest.optional_imports, 1, "optional import parses")
+eq(optionalManifest.optional_imports[1].required, false,
+  "optional import is marked non-blocking")
+local optionalRows, optionalMissing, missingOptional =
+  RequiredImports.inspect(optionalManifest, love.filesystem, fakeHash)
+eq(optionalMissing, 0, "missing optional import is not required")
+eq(missingOptional, 1, "missing optional import is reported separately")
+check(not optionalRows[1].required, "optional row is labeled optional")
+
+check(not pcall(Manifest.validate, {
+  id = "bad", name = "Bad", version = "1", entry = "main.lua",
+  required_imports = { { id = "rom", file = "../outside.z64", md5 = DIGEST } },
+}), "required import cannot escape baseroms")
+check(not pcall(Manifest.validate, {
+  id = "bad", name = "Bad", version = "1", entry = "main.lua",
+  required_imports = { { id = "rom", file = "rom.z64", md5 = "short" } },
+}), "malformed MD5 is refused")
+check(not pcall(Manifest.validate, {
+  id = "bad", name = "Bad", version = "1", entry = "main.lua",
+  required_imports = { { id = "rom", file = ".rom.removed", md5 = DIGEST } },
+}), "hidden import filenames cannot collide with engine metadata")
+check(not pcall(Manifest.validate, {
+  id = "bad", name = "Bad", version = "1", entry = "main.lua",
+  required_imports = { { id = "rom", file = "rom.bin", md5 = DIGEST,
+    max_size = RequiredImports.MAX_BYTES + 1 } },
+}), "manifest import sizes cannot exceed the hard limit")
+
+local canonical = "\128\55\18\64ABCD"
+local v64 = "\55\128\64\18BADC"
+local n64 = "\64\18\55\128DCBA"
+check(RequiredImports.importData(optionalManifest, "bonus", canonical,
+  { hash = fakeHash }), "optional import uses the normal validation path")
+eq(RequiredImports.normalizeN64(canonical), canonical, "z64 stays canonical")
+eq(RequiredImports.normalizeN64(v64), canonical, "v64 pair swap canonicalizes")
+eq(RequiredImports.normalizeN64(n64), canonical, "n64 word swap canonicalizes")
+eq(RequiredImports.normalizeN64(string.rep("H", 512) .. v64), canonical,
+  "recognized 512-byte copier header is stripped")
+check(RequiredImports.normalizeN64(string.rep("H", 520)) == nil,
+  "an arbitrary 512-byte prefix is not treated as a copier header")
+
+local ok, digest = RequiredImports.importData(manifest, "stadium2", v64,
+  { hash = fakeHash })
+check(ok, "validated bytes import")
+eq(digest, DIGEST, "import reports canonical digest")
+eq(love.filesystem.read("mods/stadium_fx/baseroms/stadium2.z64"), canonical,
+  "import writes canonical bytes inside the mod")
+local rows, missing = RequiredImports.inspect(manifest, love.filesystem, fakeHash)
+eq(missing, 0, "written import satisfies its declaration")
+check(rows[1].present, "inspection reports ready")
+
+local target = Manifest.validate({
+  id = "other_fx", name = "Other FX", version = "1.0.0", entry = "main.lua",
+  required_imports = {
+    { id = "same_rom", file = "source.z64", format = "n64", md5 = DIGEST },
+  },
+}, "mods/other_fx")
+local targetRows, targetMissing = RequiredImports.inspect(target,
+  love.filesystem, fakeHash)
+eq(targetMissing, 1, "matching hashes do not silently share another mod's import")
+check(not targetRows[1].present,
+  "a mod needs its own explicit player-selected file")
+check(RequiredImports.remove(target, "same_rom"), "a required import can be removed")
+eq(love.filesystem.read("mods/other_fx/baseroms/source.z64"), nil,
+  "remove deletes this mod's private copy")
+check(RequiredImports.importData(target, "same_rom", canonical, { hash = fakeHash }),
+  "choosing the file again clears the removal decision")
+
+local legacy = Manifest.validate({
+  id = "legacy", name = "Legacy", version = "1.0.0", entry = "main.lua",
+}, "mods/legacy")
+local legacyTarget = Manifest.validate({
+  id = "legacy_user", name = "Legacy User", version = "1.0.0", entry = "main.lua",
+  required_imports = {
+    { id = "rom", file = "legacy-source.z64", format = "n64", md5 = DIGEST },
+  },
+}, "mods/legacy_user")
+love.filesystem.write("mods/legacy/baseroms/manually-imported.v64", v64)
+local legacyRows, legacyMissing = RequiredImports.inspect(legacyTarget,
+  love.filesystem, fakeHash)
+eq(legacyMissing, 1, "undeclared files in another mod are never indexed")
+check(not legacyRows[1].present, "legacy baseroms remain private to their mod")
+
+local capped = Manifest.validate({
+  id = "capped", name = "Capped", version = "1.0.0", entry = "main.lua",
+  required_imports = {
+    { id = "small", file = "small.bin", md5 = DIGEST, max_size = 4 },
+  },
+}, "mods/capped")
+local tooLarge, sizeWhy = RequiredImports.validateData(
+  capped.required_imports[1], "12345", fakeHash)
+eq(tooLarge, nil, "per-import size cap rejects before hashing")
+check(tostring(sizeWhy):find("too large", 1, true) ~= nil,
+  "size rejection explains the limit")
+
+-- A successful validation writes an engine receipt. Matching size + modtime
+-- lets later launcher refreshes avoid reading and hashing the ROM again.
+local cacheFiles = {
+  ["mods/cache/baseroms/source.z64"] = canonical,
+}
+local dataReads = 0
+local cacheModtime = 123
+local cacheFs = {
+  getInfo = function(path, kind)
+    local data = cacheFiles[path]
+    if data then return { type = "file", size = #data, modtime = cacheModtime } end
+    return nil
+  end,
+  read = function(path)
+    if path == "mods/cache/baseroms/source.z64" then dataReads = dataReads + 1 end
+    return cacheFiles[path]
+  end,
+  write = function(path, data) cacheFiles[path] = data return true end,
+  remove = function(path) cacheFiles[path] = nil return true end,
+}
+local cacheManifest = Manifest.validate({
+  id = "cache", name = "Cache", version = "1.0.0", entry = "main.lua",
+  required_imports = {
+    { id = "source", file = "source.z64", format = "n64", size = 8,
+      md5 = DIGEST },
+  },
+}, "mods/cache")
+local cacheRows = RequiredImports.inspect(cacheManifest, cacheFs, fakeHash)
+check(cacheRows[1].present, "initial cached import validation succeeds")
+cacheRows = RequiredImports.inspect(cacheManifest, cacheFs, function()
+  error("unchanged cached import should not be hashed again")
+end)
+check(cacheRows[1].present, "validation receipt satisfies the next refresh")
+eq(dataReads, 1, "unchanged imported ROM is read only once")
+cacheFiles["mods/cache/baseroms/source.z64"] = "BADBYTES"
+cacheModtime = 124
+cacheRows = RequiredImports.inspect(cacheManifest, cacheFs, fakeHash)
+check(not cacheRows[1].present, "changed imported ROM bypasses a stale receipt")
+eq(dataReads, 2, "changed imported ROM is read again")
+eq(cacheFiles[RequiredImports.receiptPath(cacheManifest, cacheManifest.required_imports[1])],
+  nil, "stale validation receipt is removed")
+
+local rejected, why = RequiredImports.importData(target, "same_rom", "wrong",
+  { hash = fakeHash })
+eq(rejected, nil, "mismatched selection is rejected")
+check(tostring(why):find("N64 ROM (.z64/.v64/.n64)", 1, true) ~= nil,
+  "normalization failure explains the selected format")
+
+love.filesystem.write("mods/launcher_needs/manifest.json", ([[{
+  "id":"launcher_needs","name":"Launcher Needs","version":"1.0.0",
+  "entry":"main.lua","required_imports":[{"id":"source","name":"Source ROM",
+  "file":"source.bin","md5":"%s"}]
+}]]):format(DIGEST))
+love.filesystem.write("mods/launcher_needs/main.lua", "return function(mod) end")
+local launcherRows = require("src.mods.LauncherMods").list()
+eq(#launcherRows, 1, "launcher keeps a mod with a missing required import visible")
+eq(launcherRows[1].missingRequiredImports, 1,
+  "launcher row carries the missing import count")
+eq(launcherRows[1].status, "needs_import",
+  "missing import changes Ready to Import required")
+check(launcherRows[1].statusDetail:find("Source ROM", 1, true) ~= nil,
+  "launcher warning names the missing file")
+
+local function memfs(files)
+  return {
+    read = function(path) return files[path] end,
+    getInfo = function(path)
+      if files[path] then return { type = "file" } end
+      local prefix = path .. "/"
+      for key in pairs(files) do
+        if key:sub(1, #prefix) == prefix then return { type = "directory" } end
+      end
+    end,
+    getDirectoryItems = function(path)
+      if path == "mods" then
+        local out, seen = {}, {}
+        for key in pairs(files) do
+          local id = key:match("^mods/([^/]+)/manifest%.json$")
+          if id and not seen[id] then seen[id] = true; out[#out + 1] = id end
+        end
+        table.sort(out)
+        return out
+      end
+      return {}
+    end,
+    load = function(path)
+      local source = files[path]
+      if not source then return nil, "missing" end
+      return load(source, path)
+    end,
+  }
+end
+
+local manifestJson = ([[{
+  "id":"needs_rom","name":"Needs ROM","version":"1.0.0","entry":"main.lua",
+  "required_imports":[{"id":"rom","name":"Source ROM","file":"source.bin",
+  "md5":"%s"}]
+}]]):format(DIGEST)
+local loader = Loader.new({ fs = memfs({
+  ["mods/needs_rom/manifest.json"] = manifestJson,
+  ["mods/needs_rom/main.lua"] = "return function(mod) mod.exports.ran = true end",
+}) })
+check(loader:load({}) == false, "missing required import blocks the enabled mod")
+local status = loader:status().available[1]
+eq(status.state, "invalid", "blocked mod reports invalid")
+check(status.error:find("Source ROM", 1, true) ~= nil,
+  "loader failure names the required import")
+check(not (loader.exports.needs_rom and loader.exports.needs_rom.ran),
+  "blocked mod entry never executes")
+
+local optionalJson = ([[{
+  "id":"optional_rom","name":"Optional ROM","version":"1.0.0","entry":"main.lua",
+  "optional_imports":[{"id":"rom","name":"Bonus ROM","file":"bonus.bin",
+  "md5":"%s"}]
+}]]):format(DIGEST)
+local optionalLoader = Loader.new({ fs = memfs({
+  ["mods/optional_rom/manifest.json"] = optionalJson,
+  ["mods/optional_rom/main.lua"] = "return function(mod) mod.exports.ran = true end",
+}) })
+check(optionalLoader:load({}), "missing optional import does not block the mod")
+check(optionalLoader.exports.optional_rom.ran,
+  "mod entry executes without its optional import")
+
+S.finish()
diff --git a/tests/modkit_tests.lua b/tests/modkit_tests.lua
index fc5758cc..ee53aef0 100644
--- a/tests/modkit_tests.lua
+++ b/tests/modkit_tests.lua
@@ -463,6 +463,8 @@ return function(mod)
 end
 ]])
 write(bad .. "/hack.gb", "GBDATA")
+os.execute((mkdir .. " %q"):format(bad .. "/baseroms"))
+write(bad .. "/baseroms/stadium2.z64", "USER ROM")
 write(bad .. "/cachepath.lua",
   'return { pic = "assets/generated/battle/front/mew.png" }')
 
@@ -474,6 +476,8 @@ check(out:find("MK101", 1, true) ~= nil, "schema typo reported as MK101")
 check(out:find("base_stats", 1, true) ~= nil, "MK101 names the bad field")
 check(out:find("MK301", 1, true) ~= nil, "cache reference reported as MK301")
 check(out:find("MK303", 1, true) ~= nil, "ROM patch file reported as MK303")
+check(out:find("MK307", 1, true) ~= nil,
+  "a user-supplied baseroms file is refused explicitly")
 
 out, code = run(("%s tools/modkit.py pack %q -o %q --base fixture")
   :format(python, bad, root .. "/bad.modpkg"))
diff --git a/tests/rom_importer_android_mod_pick_test.lua b/tests/rom_importer_android_mod_pick_test.lua
index 6e06fece..b958e75b 100644
--- a/tests/rom_importer_android_mod_pick_test.lua
+++ b/tests/rom_importer_android_mod_pick_test.lua
@@ -14,6 +14,7 @@ love.system = love.system or {}
 local saved = {
   getOS = love.system.getOS,
   pickFile = love.system.pickFile,
+  pickFileKinds = love.system.pickFileKinds,
 }
 
 local pickCalls = {}
@@ -22,6 +23,7 @@ love.system.pickFile = function(kind)
   pickCalls[#pickCalls + 1] = kind or "rom"
   return true
 end
+love.system.pickFileKinds = function() return "rom,mod,sav,required_import" end
 
 local function freshImporter(ready)
   return setmetatable({
@@ -94,11 +96,83 @@ eq(ri._imported.source, "picked_save.sav", "focus reads the SAF save filename")
 check(love.filesystem.getInfo("picked_save.sav") == nil,
   "successful focus import removes picked_save.sav")
 
+-- Required mod files use their own safe picker kind and pending filename.
+pickCalls = {}
+ri = freshImporter({ red = true, blue = true })
+ri.nativePicker = true
+ri.mobileFileBridge = true
+ri.mods = { {
+  id = "needs_source",
+  manifest = { id = "needs_source", name = "Needs Source",
+    required_imports = { { id = "source", name = "Source", file = "source.bin",
+      format = "raw", md5 = { "00000000000000000000000000000000" } } } },
+} }
+ri:chooseRequiredImport("needs_source", "source")
+eq(pickCalls[1], "required_import",
+  "required file asks for the dedicated picker kind")
+eq(ri.pickerPendingModId, "needs_source", "pending mod is remembered")
+eq(ri.pickerPendingImportId, "source", "pending import is remembered")
+
+-- A rejected selection stays on the imported-files page, where the player can
+-- see it before choosing another file, instead of behind the modal.
+ri.nativePicker = false
+ri._importRequiredData = RomImporter._importRequiredData
+local savedData = love.data
+love.data = {
+  hash = function() return "not accepted" end,
+  encode = function() return "ffffffffffffffffffffffffffffffff" end,
+}
+ri:_importRequiredData("needs_source", "source", "wrong source bytes")
+love.data = savedData
+check(ri.requiredImportNotice ~= nil,
+  "required import rejection creates an in-modal notice")
+eq(ri.requiredImportNotice.modId, "needs_source",
+  "required import notice identifies its mod")
+eq(ri.requiredImportNotice.importId, "source",
+  "required import notice identifies its file")
+check(ri.requiredImportNotice.text:find("MD5 mismatch", 1, true) ~= nil,
+  "required import notice includes the MD5 failure")
+check(ri.modNotice == nil,
+  "required import rejection is not hidden in the general Mods notice")
+
+-- Reported size is checked before the selected file is read into Lua.
+local savedGetInfo = love.filesystem.getInfo
+love.filesystem.getInfo = function(name, kind)
+  if name == "oversized_required.bin" then
+    return { type = "file", size = 10 }
+  end
+  return savedGetInfo(name, kind)
+end
+ri.mods[1].manifest.required_imports[1].max_size = 4
+ri._importRequiredSource = RomImporter._importRequiredSource
+ri._importRequiredData = function(self) self._oversizedWasRead = true end
+ri:_importRequiredSource("needs_source", "source", "oversized_required.bin")
+check(not ri._oversizedWasRead, "oversized required file is rejected before import")
+check(ri.requiredImportNotice.text:find("too large", 1, true) ~= nil,
+  "oversized required file reports its size error in the modal")
+ri.mods[1].manifest.required_imports[1].max_size = nil
+love.filesystem.getInfo = savedGetInfo
+
+ri.nativePicker = true
+ri._importRequiredSource = function(self, modId, importId, source)
+  self._requiredImported = { modId = modId, importId = importId, source = source }
+  return true
+end
+love.filesystem.write("picked_required_import.bin", "source bytes")
+ri:focus(true)
+check(ri._requiredImported ~= nil, "focus consumes a required-file SAF pick")
+eq(ri._requiredImported.modId, "needs_source", "focus routes to the pending mod")
+eq(ri._requiredImported.importId, "source", "focus routes to the pending declaration")
+check(love.filesystem.getInfo("picked_required_import.bin") == nil,
+  "focus removes the staged required-file pick")
+
 love.system.getOS = saved.getOS
 love.system.pickFile = saved.pickFile
+love.system.pickFileKinds = saved.pickFileKinds
 -- leftover cleanup if a failed assertion left files behind
 love.filesystem.remove("usb_mod.zip")
 love.filesystem.remove("picked_mod.zip")
 love.filesystem.remove("picked_save.sav")
+love.filesystem.remove("picked_required_import.bin")
 
 S.finish()
diff --git a/tools/modkit.py b/tools/modkit.py
index 42fc5acd..64b212d5 100644
--- a/tools/modkit.py
+++ b/tools/modkit.py
@@ -1045,6 +1045,14 @@ def lint_dir(repo, mod_dir, manifest):
     for rel in mod_files(mod_dir):
         path = os.path.join(mod_dir, rel)
         ext = os.path.splitext(rel)[1].lower()
+        # MK307: required_imports are user-owned installation state. Keeping
+        # baseroms in the walk without an explicit gate would let `pack`
+        # silently bundle exactly the ROM this feature exists not to ship.
+        if rel.startswith("baseroms/"):
+            findings.append(Finding(
+                "MK307", "error",
+                "user-supplied baseroms must not be distributed", rel))
+            continue
         # MK301: nothing may live in (or point into) the generated trees
         if rel.startswith(("data/generated/", "assets/generated/")):
             findings.append(Finding(