fix(installer): use Limine on 32-bit UEFI firmware

Atom Bay Trail / Cherry Trail mini-PCs and tablets have a 64-bit CPU behind
32-bit UEFI. We picked systemd-boot there (Arch ships no ia32 build), and
archinstall 4.4's GRUB path hardcodes --target=x86_64-efi, so the installed
system could not boot. archinstall's Limine path copies both BOOTIA32.EFI
and BOOTX64.EFI and chooses the entry by /sys/firmware/efi/fw_platform_size;
the default layout's FAT /boot satisfies its layout check. 64-bit UEFI and
BIOS keep systemd-boot / GRUB.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Wq1hzUp4ZmCKHDuLKCnu73

tests/test_app.py

@@ -390,3 +390,16 @@ def test_error_page_offers_retry(monkeypatch, tmp_path):
     html = app_module.app.test_client().get("/install/log").get_data(as_text=True)
     assert "Try again" in html
     assert "next-steps" not in html
+
+
+def test_detect_bootloader_by_firmware(tmp_path):
+    import app as app_module
+
+    efi = tmp_path / "efi"
+    assert app_module._detect_bootloader(efi) == "Grub"  # BIOS / legacy
+    efi.mkdir()
+    assert app_module._detect_bootloader(efi) == "Systemd-boot"  # no bitness file
+    (efi / "fw_platform_size").write_text("64\n")
+    assert app_module._detect_bootloader(efi) == "Systemd-boot"
+    (efi / "fw_platform_size").write_text("32\n")
+    assert app_module._detect_bootloader(efi) == "Limine"

webinstaller/app.py

@@ -515,10 +515,20 @@ def _post_install_commands(hostname, admin_username, admin_password):
     ]
 
 
-def _detect_bootloader():
+def _detect_bootloader(efi_dir=Path("/sys/firmware/efi")):
     # systemd-boot is UEFI-only; on BIOS/legacy it trips HardwareIncompatibilityError
     # inside archinstall. /sys/firmware/efi exists iff we were booted via UEFI.
-    return "Systemd-boot" if Path("/sys/firmware/efi").exists() else "Grub"
+    if not efi_dir.exists():
+        return "Grub"
+    # 64-bit CPU behind 32-bit UEFI (Atom Bay Trail / Cherry Trail mini-PCs
+    # and tablets): Arch ships no ia32 systemd-boot, and archinstall's GRUB
+    # path hardcodes --target=x86_64-efi. Its Limine path installs both
+    # BOOTIA32.EFI and BOOTX64.EFI and picks the entry by firmware bitness.
+    try:
+        bitness = (efi_dir / "fw_platform_size").read_text().strip()
+    except OSError:
+        bitness = "64"
+    return "Limine" if bitness == "32" else "Systemd-boot"
 
 
 def build_archinstall_config(s):