feat(saves): the resolver answers where a save lives and what it consists of

[danielcopper]

Which files make up a game's save is a hand-maintained table in this repo (domain/save_extensions.py), keyed by system, written from a one-pass core audit. The vendored resolver answers the same question per emulator, from the machine, with provenance. This cut hands the question over and deletes the table.

Pins emu-atlas 0.13.0 as the first commit.

What the table gets wrong today

Measured on a stock RetroDECK against the resolver, for the systems the table has entries for:

system	the table	the machine
Neo Geo Pocket	.flash, from a desk audit	.flash, read out of the core
Amiga	.nvr	no separate save file at all — the writes go into the disk image
Amiga CD32	.nvr	.nvr
3DO	the three default extensions	<rom>.<n>.srm, with a version digit the table never had
Saturn	three extensions, all treated as progress	two are progress, one is console configuration

So for Amiga the plugin searches forever for a file that cannot exist, and for 3DO it searches for a name no core writes. Neither is visible: the search simply finds nothing.

What lands

A new adapter behind a Protocol answers, per ROM and per the emulator that would launch it: the directory, the file set, the granularity, any hole left in the names, the caveats, and the link-resolved backing directory. Services see a domain value object and never a resolver type, as the firmware seam already does.

The save search and the download target take their file set from that answer. A file whose role is configuration rather than progress is not synced — the resolver states the role, and on a stock RetroDECK that is the Saturn console-settings file and MAME's per-game settings file.

The answer also classifies the save into one of five states, and the sync refuses in four of them rather than probing for a file that cannot be there:

1. one file per game — sync as today, any number of files
2. shared card — one file many games write, so per-game sync would overwrite other games' progress
3. the save is inside the game file — there is nothing separate to sync
4. names known, an identifier missing — the resolver names the files but one part of the name comes from the game's own id, which nothing here supplies
5. nothing established — the core was never audited, the emulator has no card, or the directory is known and its file names are not

The state's scope is the emulator, never the platform: PS2 is not unsupported, the standalone PCSX2 is, and the libretro core for the same platform can answer differently.

The states reach the game-detail payload in this cut. Rendering them is the next cut, so nothing about the tab changes yet — what changes is that the sync stops looking where it cannot find anything.

What dies

domain/save_extensions.py and its tests. Nothing replaces it: for the systems it covered, the resolver's answer is at least as good and in four cases better.

Decisions this cut carries

• The question goes to the catalogue entry that would launch the ROM, not to a bare core, so a standalone emulator answers for itself.
• Answers may be cached for display; every sync path asks live, because the user changes core options in the emulator's own quick menu between a launch and the next sync.
• Reads and writes use the path the emulator opens. The link-resolved path is for identity questions only.
• Saves are not zipped. One row per file stays the interoperable shape for the flat sibling files this plugin syncs; the reasoning and the ecosystem measurement are on feat(saves): store multi-file saves as a single zip asset where supported (RomM-native integrity) #1235.

Tests

• The five states, each from a real resolver answer over a fixture machine, including the two shapes inside state 5 (never audited, versus directory known and names not).
• A configuration-role file is offered by the answer and excluded from the synced set.
• A refusal in states 2 to 5 leaves no probe and writes no state.
• The systems the deleted table covered each keep or improve their answer, pinned per system.
• The plugin's platform map produces only systems the resolver knows, minus the two no ES-DE system declares.

Acceptance on the reference machine

A Game Boy Advance game syncs exactly as before. A Saturn game syncs its two progress files and no longer syncs the console-settings file, which is the configuration-role rule above doing its job — the file stays on disk and on the server, it stops being managed. The Neo Geo Pocket file is still found. Nothing is probed for Amiga any more. No game-detail page changes visibly.

Out of scope

Rendering the states (next cut). The stored save directory and the retirement of the path math (the cut after). Offering to switch a core off its shared card (#1645). Zipped saves (#1235). Identity from ROM binaries (#1462). Carrying a save when the emulator changes (#1857). Saves inside the game file (#1856).