[kfox]

Builds on #72 (the GEOS 64 user guide); merge that first. Until then this PR also shows its commit.

Saving GeoRAM (SaveRAMBanksReplacing) writes georam.tmp, renames georam.ram to georam.bak, then renames georam.tmp to georam.ram. If power drops between the two renames, there is no georam.ram on the card, and GEOS starts with empty GeoRAM even though the new save (.tmp) and the previous one (.bak) are both there.

With this change, the GeoRAM preload (LoadRAMBanksReplaced in RAMBanks.c, next to the save) falls back when georam.ram is missing:

1. georam.tmp, but only if its size is exactly the full GeoRAM image. Any other size is a torn write and is skipped.
2. otherwise georam.bak.
3. otherwise the same behaviour as before (not found, empty GeoRAM).

The GEOS 64 user guide says that the next launch after a power loss during a save loads the newest complete save. Serial logs which file was loaded. Nothing is renamed or repaired at load time: the next save already handles a missing georam.ram. The .tmp/.bak extensions are now shared constants, so save and load use the same names. The REU preload is unchanged, because the REU saves to numbered files rather than replacing one.

Verification

• npm run build:tr and npm run build:tr-plus: both build.
• npm test: 258 pass, 0 fail.
• No host test harness reaches RAMBanks.c, so the fallback has no automated test.
• Not hardware-tested.

Review

One single-pass code review at medium effort found no defects. It traced every point where power could drop during the save against the new load order. It also noted one limitation: if the GeoRAM size changes between boots (it depends on free RAM), a complete .tmp is skipped and .bak is loaded instead. That is the intended conservative choice.

[SensoriumEmbedded]

Thank you Kelly!
Hardware testing: what I ran

Four card states on a TR+ with this merged onto main, using 512K images whose every page carries a tag so the saved georam.ram shows which file was loaded. All four passed:

• georam.ram missing, complete .tmp plus .bak: serial Not found, loading: /georam.tmp, 512K read; after an Alt save georam.ram held the .tmp image and .bak was untouched.
• georam.ram missing, a 100,000-byte .tmp plus .bak: Skipping /georam.tmp: 100000 Bytes, then the .bak loaded; the save wrote the .bak image to georam.ram.
• georam.ram missing, a .tmp one page too long, no .bak: Skipping /georam.tmp: 524544 Bytes, Not found!, GEOS still started; the save produced a fresh 512K georam.ram.
• georam.ram present plus a stale complete .tmp: georam.ram loaded with no fallback line; the save rotated it to .bak and the .tmp was consumed.