fs rewrite stage 1: persistent block device (bounce buffer, cart SRAM)

- blk.asm: read_block/write_block move 256-byte blocks between battery-backed
  cart-RAM banks (8-11, the 'disk') and a WRAM bounce buffer. Banking is hidden
  in those two routines; they inline the 'restore my bank' step so they never
  touch the stack while the disk bank is mapped over the process's $A000 window
  (the stack lives there too -- a call/ret would rug-pull it).
- format-on-first-boot: superblock magic in block 0; otherwise the disk persists.
- cart RAM bumped to 128 KiB (-r 4); process banks 0-7, disk banks 8-11.
- debug tool 'blk fill/peek' + syscalls to validate round-trip and persistence.
- verified: round-trip incl. cross-bank (block 100 -> bank 11); block survives a
  reboot via .sav; magic intact (no reformat on 2nd boot).
- old WRAM 8-slot FS still backs the tools until stages 2-3.

1 files changed, 8 insertions, 1 deletions

diff --git a/src/boot.asm b/src/boot.asm
index 7c175ce..1f4a048 100644
--- a/src/boot.asm
+++ b/src/boot.asm
@@ -49,7 +49,14 @@ KernelInit:
     call ClearKernelRAM
     call CopyHramCode           ; move context-switch trampoline into HRAM
     call ProcInit               ; wipe process table
-    call fs_init                ; set up the RAM filesystem
+    ; point wCurProc at the (zeroed) kernel PCB so disk I/O during boot restores
+    ; RAM bank 0 after each block transfer (wKernelPCB.PROC_RAMB = 0).
+    ld a, LOW(wKernelPCB)
+    ld [wCurProc], a
+    ld a, HIGH(wKernelPCB)
+    ld [wCurProc+1], a
+    call blk_init               ; format the disk if needed (persists otherwise)
+    call fs_init                ; (legacy WRAMX filesystem, still used by tools)
 
     ; --- spawn the init task (pid 1); it fork()s the rest ---
     ld hl, TaskInit