Every hard-won rule, in one place:
- -Os only. -O2 miscompiles this kernel. This is not negotiable and it is not a suggestion.
- The kernel ceiling is 560KB and it is physics, not policy. Twice tested, twice failed. Past that you're in BIOS scratch memory.
- When you run out of space, move assets to disk. This has worked every single time it's been tried, from the Raycaster in V22 to the wallpapers in V46.
- 16-bit vs 32-bit encoding matters more than it looks. One wrong prefix byte in a far jump is a triple fault.
- The BIOS will clobber your unreal-mode segments during disk reads. There is no clever way around this.
- Boot-time and desktop-time are different worlds. A decoder that's perfectly safe once the desktop is up will destroy the kernel stack at boot.
- Config bugs hide behind cosmetic complaints. "The wallpaper isn't right" turned out to be three separate CMOS collisions.
- Every edit gets asserted. Search-and-replace with a hard assertion that exactly one match was found — if the assertion fails, nothing is written, and the unchanged binary size gives it away immediately.
- Back up at every verified boot. Not at every good idea. At every green light from real hardware.