Display fixes for UTM/Mac black screen issue:
- Remove MULTIBOOT_HEADER_TAG_FRAMEBUFFER from multiboot2 header (was required,
requesting text mode depth=0 which confused GRUB on some platforms)
- Add COM1 serial port (0x3F8) output alongside debugcon for UTM serial capture
- Change VGA background from black to dark blue for diagnostics
- Add early canary write to 0xB8000 ('COS' in magenta) before subsystem init
- print_hex now outputs to both debugcon and COM1
New ls command and SYS_READDIR syscall:
- SYS_READDIR (10): reads directory entries via VFS
- VFS root listing: vfs_readdir handles '/' by iterating mount table
- apps/ls: lists CWD contents, appends '/' for directories
- apps/libc/syscalls.h: readdir() wrapper
When GRUB is configured with multiboot2, it may provide a graphical
(RGB) framebuffer instead of legacy VGA text mode. This happens on
UTM/QEMU on macOS and other configurations where the bootloader
switches to a pixel-based display.
- Parse multiboot2 framebuffer tag in kernel_main to detect display mode
- Identity-map the framebuffer address (often at 0xFD000000+) after
paging is enabled, with write-through caching
- Add framebuffer.h describing the boot-time display info
- Embed 8x16 VGA bitmap font (font8x16.h) for pixel-mode rendering
- Rewrite VGA driver to support both text mode and pixel mode:
- Text mode: unchanged behavior writing to 0xB8000
- Pixel mode: renders characters using the bitmap font to the
GRUB-provided framebuffer, with proper VGA color palette mapping
- Auto-detects mode from fb_info at init time
- Multiboot2 header now requests text mode via framebuffer tag, but
gracefully falls back to pixel rendering if GRUB provides RGB
- Reverted grub.cfg gfxpayload=text (caused display issues on UTM)
Tested: boots in both text mode and graphical framebuffer mode.
- Created VGA driver that writes to the 0xB8000 text-mode framebuffer.
Supports 80x25 display with 16 foreground/background colors, scrolling,
hardware cursor updates, and special characters (\n, \r, \t, \b).
- Provides vga_puts, vga_putchar, vga_put_hex, vga_put_dec, vga_set_color.
- Displays boot banner ("ClaudeOS v0.1 booting...") on screen clear.
- vga_show_mem_stats() prints total RAM, kernel start/end addresses, and
kernel size on the VGA display during boot.
- Registered as the first driver using REGISTER_DRIVER, proving the
driver framework works end-to-end (probe -> init lifecycle).
Tested: driver loads successfully, debug port confirms vga probe/init.
