docs: sync KB — troubleshooting.md

gaming/troubleshooting.md

@@ -214,45 +214,56 @@ For full HDR setup (vk-hdr-layer, KDE config, per-API env vars), see the **steam
 
 **Diagnostic tip**: Look for rapid retry patterns in Pi-hole logs (same domain queried every 1-3s from the Xbox IP) — this signals a blocked domain causing timeout loops.
 
-## Gray Zone Warfare — EAC Failures on Proton (2026-03-31)
+## Gray Zone Warfare — EAC Failures on Proton (2026-03-31) [RESOLVED]
 
 **Severity:** High — game unplayable online
+**Status:** RESOLVED — corrupted prebuild world cache file
 
-**Problem:** EAC errors when connecting to servers on Linux/Proton. Two error codes observed:
-- `0x0002000F` — "The client failed to register in time" (EAC timeout)
-- `0x00020011` — "The client failed to start the session" (EAC session init failure)
+**Problem:** EAC errors when connecting to servers on Linux/Proton. Three error codes observed across attempts:
+- `0x0002000A` — "The client failed an anti-cheat client runtime check" (the actual root cause)
+- `0x0002000F` — "The client failed to register in time" (downstream timeout)
+- `0x00020011` — "The client failed to start the session" (downstream session failure)
 
-Game launches fine, EAC bootstrapper reports success ("Easy Anti-Cheat successfully loaded in-game"), but fails when joining a server at "Synchronizing Live Data".
+Game launches fine, EAC bootstrapper reports success, but fails when joining a server at "Synchronizing Live Data".
 
-**Root Cause:** EOS SDK cannot load `steam_api64.dll` at startup:
+**Root Cause:** A corrupted/stale prebuild world cache file that EAC flagged during runtime checks:
 ```
-LogEOSSDK: Error: Unable to load the Steamworks library: steam_api64.dll
-LogEOSSDK: Error: Integrated Platform Steam failed to get steamworks sdk
+LogEOSAntiCheat: [AntiCheatClient] [PollStatusInternal] Client Violation with Type: 5
+Message: Unknown file version (GZW/Content/SKALLA/PrebuildWorldData/World/cache/0xb9af63cee2e43b6c_0x3cb3b3354fb31606.dat)
 ```
-Without Steam integration, EOS has no user identity → `Invalid user EOS ID` → EAC cannot start a client session. The `steam_api64.dll` exists in the game tree at `Engine/Binaries/ThirdParty/Steamworks/Steamv158/Win64/` but EOS isn't resolving that path under Wine/Proton.
+EAC scanned this file, found an unrecognized version, and flagged a client violation. The other errors (`0x0002000F`, `0x00020011`) were downstream consequences — EAC couldn't complete session registration after the violation.
 
-Additionally: upgrading from GE-Proton9-25 to GE-Proton10-25 and nuking the compatdata prefix may have triggered the regression. **The game was working earlier the same day on GE-Proton9-25.**
+Compounding factors that made diagnosis harder:
+- Epic EOS scheduled maintenance (Fortnite v40.10, Apr 1 08:00-09:30 UTC) returned 503s from `api.epicgames.dev/auth/v1/oauth/token`, masking the real issue
+- `steam_api64.dll` EOS SDK errors at startup are **benign noise** under Proton — red herring
+- Nuking the compatdata prefix and upgrading Proton happened concurrently, adding confusion
+
+**Fix:**
+1. Delete the specific cache file: `rm "GZW/Content/SKALLA/PrebuildWorldData/World/cache/0xb9af63cee2e43b6c_0x3cb3b3354fb31606.dat"`
+2. Verify game files in Steam — Steam redownloads a fresh copy with different hash
+3. Launch game — clean logs, no EAC errors
+
+Key detail: the file was the same size (60.7MB) before and after, but different md5 hash — Steam's verify replaced it with a corrected version.
 
 **Log locations:**
 - EAC bootstrapper: `compatdata/2479810/pfx/drive_c/users/steamuser/AppData/Roaming/EasyAntiCheat/.../anticheatlauncher.log`
 - Game log: `compatdata/2479810/pfx/drive_c/users/steamuser/AppData/Local/GZW/Saved/Logs/GZW.log`
 - STL launch log: `~/.config/steamtinkerlaunch/logs/gamelaunch/id/2479810.log`
 
-**What was tried (did NOT fix):**
-1. Installed Proton EasyAntiCheat Runtime (AppID 1826330)
-2. Deleted stale world cache (`GZW/Content/SKALLA/PrebuildWorldData/World/cache/`)
-3. Nuked compatdata prefix for clean rebuild
-4. Verified game files (Steam repaired 20 files)
-5. Upgraded to GE-Proton10-25
+**What did NOT fix it (for reference):**
+1. Installing Proton EasyAntiCheat Runtime (AppID 1826330) — good to have but not the issue
+2. Deleting the entire cache directory without re-verifying — Steam verify re-downloaded the same bad file the first time (20 files fixed); needed a second targeted delete + verify
+3. Nuking compatdata prefix for clean rebuild
+4. Switching Proton versions (GE-Proton9-25 ↔ GE-Proton10-25)
 
-**What to try next:**
-1. **Restore GE-Proton9-25** — the version that was working earlier. Old prefix backed up at `compatdata/2479810.bak`
-2. **Check Proton issue [#7721](https://github.com/ValveSoftware/Proton/issues/7721)** — master tracking issue for GZW on Proton
-3. **`split_lock_detect=off`** kernel param — reported to help with EAC init timeouts on some systems
-
-**Lesson:** Don't upgrade Proton versions on a game that's currently working. Pin working Proton versions per-game in STL configs and only upgrade intentionally with a rollback plan (keep the old compatdata prefix).
+**Lessons:**
+- When EAC logs show "Unknown file version" for a specific `.dat` file, delete that file and verify — don't nuke the whole cache or prefix
+- `steam_api64.dll` EOS errors are benign under Proton and not related to EAC failures
+- Check Epic's status page for scheduled maintenance before deep-diving Proton issues
+- Multiple verify-and-fix cycles may be needed — the first verify can redownload a stale cached version from Steam's CDN
 
 **Game version:** 0.4.0.0-231948-H (EA Pre-Alpha)
+**Working Proton:** GE-Proton10-25
 **STL config:** `~/.config/steamtinkerlaunch/gamecfgs/id/2479810.conf`
 
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