fix: give the bare platform menu its default

With nothing detected, the menu had no Enter default, while --help and
the --dest menu name RetroArch as the fallback. Its title now also says
why the question is asked.

install.ps1

@@ -11,7 +11,7 @@
 
     $ErrorActionPreference = "Stop"
     $defaultInstallUrl = "https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-    $defaultInstallSha256 = "d32af09905abef095c8e5e8fa832fbc76d1556e9cd099b81227d68d1d66d2915"
+    $defaultInstallSha256 = "8cfe5cb80b8df7f8c2736cfe5855a768c3eacad6ebf5bfd7336b3b4f5a4d5d76"
     $maximumInstallerBytes = 2MB
     $installerExit = 0
     $installer = if ($PSScriptRoot) { Join-Path $PSScriptRoot "install.py" } else { $null }

install.py

@@ -5603,7 +5603,8 @@ def _choose_platform(title: str, default: str = "") -> str:
 
 def _prompt_manual_platform(os_type: str) -> list[tuple[str, Path]]:
     """Ask for a platform and a BIOS directory when nothing was detected."""
-    plat = _choose_platform("Choose the platform to install for:")
+    plat = _choose_platform("No supported platform found here. Choose the one to "
+                            "install for:", "retroarch")
     default_dest = _default_dest(os_type, plat)
     raw = ""
     while not raw:

install.sh

@@ -18,7 +18,7 @@ esac
 TEMP_INSTALLER=""
 TEMP_DIRECTORY=""
 DEFAULT_INSTALL_URL="https://raw.githubusercontent.com/Abdess/retrobios/main/install.py"
-DEFAULT_INSTALL_SHA256="d32af09905abef095c8e5e8fa832fbc76d1556e9cd099b81227d68d1d66d2915"
+DEFAULT_INSTALL_SHA256="8cfe5cb80b8df7f8c2736cfe5855a768c3eacad6ebf5bfd7336b3b4f5a4d5d76"
 MAX_INSTALLER_BYTES=2097152
 
 cleanup() {

tests/test_install.py

@@ -1808,6 +1808,16 @@ class TestManualPlatformPrompt(unittest.TestCase):
             chosen, [("retroarch", Path.home() / ".config" / "retroarch" / "system")]
         )
 
+    def test_enter_takes_retroarch_as_the_dest_menu_does(self):
+        """The --dest menu offered `[Enter for RetroArch]` and this one, the
+        same list, had no default."""
+        answers = iter(["", ""])
+        out = io.StringIO()
+        with unittest.mock.patch("builtins.input", lambda _prompt="": next(answers)), \
+                contextlib.redirect_stdout(out):
+            chosen = install._prompt_manual_platform("linux")
+        self.assertEqual(chosen[0][0], "retroarch")
+
     def test_name_and_explicit_directory(self):
         answers = iter(["batocera", "~/my bios"])
         with unittest.mock.patch("builtins.input", lambda _prompt="": next(answers)):