Fix IClientRemoteStorage FileExists hook ABI for current Steam

[wtfseanscool]

Summary

Updates the IClientRemoteStorage::FileExists hook to match the current Steam client's internal method ABI.

The hook now receives and forwards:

• void* pThis
• AppId_t appId
• uint32_t fileRoot
• const char* pchFile

Instead of reading the AppID from the hard-coded pThis + 0x38 object offset, the hook now uses the explicit AppID argument and substitutes the active-route real AppID when required.

Current Steam validation

Steam build:

1788400362

steamclient64.dll SHA-256:

caba4826aa3501039d095aee1843a6bfb270fb43a3ab4455b2d6733223579fee

SteamUI.dll SHA-256:

cb387adefbbac64a3c1490d4275d00daf3a1e0219b4580726ef7681db7429278

The current IClientRemoteStorage::FileExists target was resolved at:

steamclient64.dll RVA 0x74FFF0

The current-build pattern set was verified against the installed DLLs.

Result:

ALL RUNTIME PATTERNS VALID

Runtime validation

Tested with the locally built Release LumaCore.dll loaded into the current Steam client.

Observed:

• LumaCore.dll loaded successfully into steam.exe
• both current Steam TOMLs loaded from local cache
• hooks_installed = 42
• hooks_missed = []
• steamui_attach_state = attached
• startup injection completed successfully
• cloud/remote-storage path exercised successfully
• Steam remained stable through real launch and cloud-sync testing

Build validation

A clean x64 Release build completed successfully using MSVC and:

LumaCore/build.bat --release-only --no-pause --clean

Scope

This PR contains only the LumaCore hook ABI correction.

The corresponding per-build Steam pattern files are handled separately in the pattern repository consumed by SFF.