folder structure (top level folder = dat entry):
```
app1
depot1
CSM/CSD with all depot chunks
all depot manifests
depot key
depot2
...
possibly sidecar file with update history (for correct manifest combos). current manifest combos can be retreived via steam. could include historical data from steamdb, marked as such.
```
chunks and manifests are to be the raw files from the server
when a new manifest is pushed, the CSM/CSD file would be updated (added as new file, with old file excluded from DoM?) and new manifest file added
unsolved issues:
* tooling to automate all this
* recording package info, so that "trap DLC" DRM can be avoided
* recording achievement info, so that can be used offline with steam emulators
* SmartSteamEmu is closed source and windows only (its apparently the best steam emulator - hooks API calls instead of replacing DLLs, has achievement display)