bugfix(savegame): Guard GameLogic xfer version bump with RETAIL_COMPATIBLE_XFER_SAVE

[bobtista]

Summary

• Guards the xfer version bump in GameLogic::xfer behind RETAIL_COMPATIBLE_XFER_SAVE, replacing the unconditional bump from fix(object): Save and load game object list in correct order #2161
• When retail compatible: keeps original version (10 for GeneralsMD, 9 for Generals), saves objects in forward order, and always reverses the object list after load to fix the prepend-induced reversal
• When not retail compatible: bumps the version (11 for GeneralsMD, 10 for Generals), saves objects in reverse order so they load in correct order without post-load fixup

Test plan

• Save and load a game, verify object list order is correct
• Load a pre-existing save file, verify it loads without error and object order is correct

[greptile-apps]

Greptile Summary

This PR refines the fix from #2161 by guarding the Xfer version bump and reverse-save iteration behind #if !RETAIL_COMPATIBLE_XFER_SAVE rather than committing to a permanent version bump. Since RETAIL_COMPATIBLE_XFER_SAVE defaults to 1 in Core/GameEngine/Include/Common/GameDefines.h, default builds retain version 9 (Generals) / version 10 (Zero Hour) compatibility with retail saves, while the post-load list reversal is now unconditionally applied to all saves at or below those version thresholds to correct prepend-induced ordering.

• Version gating: currentVersion is now 9 (Generals) or 10 (Zero Hour) in default builds, restoring the ability to load those saves with unmodified retail code.
• Save-path branching: Forward-order iteration is used in the retail-compatible path; reverse-order iteration is preserved under #if !RETAIL_COMPATIBLE_XFER_SAVE.
• Load-path unification: The in-place linked-list reversal now applies to all version ≤ 9/10 saves, covering both old retail saves and new retail-compatible saves; no reversal is done for version 10/11 (non-retail path) saves that were already saved in reverse order.
• Saves created under PR fix(object): Save and load game object list in correct order #2161 (version 10 / 11 in Generals / Zero Hour respectively) will trigger XFER_INVALID_VERSION when loaded by a default (RETAIL_COMPATIBLE_XFER_SAVE=1) build, as currentVersion is now lower than the stored version. This is an acknowledged and intentional trade-off noted in the PR description.

Confidence Score: 4/5

• Safe to merge for default builds; the logic covering all three save/load version scenarios is correct and well-documented.
• The core logic — guarding the version bump and reverse-iteration behind RETAIL_COMPATIBLE_XFER_SAVE, then unconditionally reversing at load time for all sub-threshold versions — is verified correct for every scenario (old retail saves, new retail-compatible saves, new non-retail saves). The only known breakage (saves from the narrow PR fix(object): Save and load game object list in correct order #2161 window) is intentional and documented. No new serialized fields are introduced.
• No files require special attention; both changed files are symmetric mirrors of the same fix.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[GameLogic::xfer called] --> B{XFER_SAVE or XFER_LOAD?}

    B -->|SAVE| C{RETAIL_COMPATIBLE_XFER_SAVE?}
    C -->|Yes - version 9/10| D[Iterate forward: getFirstObject → getNextObject]
    C -->|No - version 10/11| E[Find lastObj, iterate backward: getPrevObject]
    D --> F[Write objects newest-first]
    E --> G[Write objects oldest-first]

    B -->|LOAD| H[Create & prepend each object during load]
    H --> I{saved version <= 9 or <= 10?}
    I -->|Yes - forward-saved file| J[Reverse linked list in-place]
    I -->|No - reverse-saved file version 10+/11+| K[No reversal needed]
    J --> L[List order: newest at head]
    K --> L

Loading

_{Last reviewed commit: 805d193}

[xezon]

Looks correct to me.

Did you test it? Does it work?