D028 - The param.sfo reader comes from SELFish, the in-place writer stays

Status: decided Date: 2026-09-26

param.sfo is read through selfish_title::sfo::Sfo. pros_core::sfo keeps only what Prosperous adds: the account id rendered as hex, and set, which overwrites one value in place within the room the file already has.

Why: platform formats come from SELFish, and a second layout table drifts. graft depends on editing a save rather than rebuilding it, because a reassembled file still parses and is refused later by the target with nothing pointing at the wrong byte.

Rejected:

• A parser of Prosperous's own: a duplicate of a platform format.
• Sfo::to_bytes for writes: re-serialises the whole file.