debugging-linux-games

Debugging Linux Games (Research-First)

Overview

Steam-on-Linux problems almost always have a documented community fix. The documented fix is usually a game launch option, an env var, a config tweak, or a known proton-ge / proton-cachyos release with a workaround baked in — NOT a patch to dxvk-nvapi or vkd3d-proton. Diving into shim code without checking first is how 10 hours get spent producing patches that the actual fix renders unnecessary.

Core principle: Community research first. Code second. Always.

Iron Law: NO patches, forks, overlays, postFixup drops, or any code changes to the Wine/Proton/DXVK/vkd3d/gamescope stack until the six-source research checklist below has been completed within a 30-minute time-box. If a launch option, env var, config flag, or proton-ge build already solves the problem, that's the answer — even if reading the source feels more satisfying. No exceptions.

Announce at start: "I'm using debugging-linux-games to research before touching code."

Rigidity Level

LOW FREEDOM — The research phase is mandatory. The 30-minute time-box is mandatory. The "no shims until research is done" gate is mandatory.

The Six-Source Checklist

Time-box: 30 minutes. Stop earlier if a documented fix matches the symptom.

For RE Engine / Capcom titles specifically: check whether /WineDetectionEnabled:False is documented as a launch option — Capcom's RE Engine games (MH Wilds, PRAGMATA, RE4R, DD2) gate RT/PT/DLSS-RR behind an internal Wine detection check.

The Process

Phase 1: Identify Game + Engine + Stack

Before searching, gather:

• Game title + Steam app ID (the app ID makes ProtonDB / Steam community search precise)
• Engine (RE Engine, Unreal 4/5, Unity, Source 2, etc.) — engines tend to share fixes
• Stack (proton version, GPU vendor + arch, compositor, gamescope yes/no, kernel)
• Exact symptom (full error text or screenshot, not paraphrased)
• What the user already tried

For NixOS + proton-cachyos + Blackwell + niri specifically: most "X is broken in gamescope" reports translate to "use PROTON_USE_WAYLAND=1 and skip gamescope, then check the title-specific fix."

Phase 2: Six-Source Research (30 min, time-boxed)

Dispatch parallel research:

Agent (general-purpose, parallel × 2)
  description: "ProtonDB + Steam community search for <title>"
  prompt: |
    Find the working Linux/Proton configuration for <title> (Steam app
    ID <id>). Check:
    - protondb.com/app/<id> — top reports, recommended proton version,
      launch options listed
    - steamcommunity.com/app/<id>/discussions — filter for Linux/Wine/Proton
    - r/linux_gaming and the game's subreddit
    Report: (a) launch options that consistently work, (b) known issues
    list with workarounds, (c) any "do not use gamescope" or "use proton-ge
    X.Y" notes. Under 300 words.

Agent (general-purpose, parallel × 2)
  description: "GitHub issues + PCGamingWiki for <title>/<engine>"
  prompt: |
    Search:
    - github.com/ValveSoftware/Proton issues (open + closed) for "<title>"
      and "<engine>"
    - HansKristian-Work/vkd3d-proton, doitsujin/dxvk, jp7677/dxvk-nvapi
      issues for the same
    - ValveSoftware/gamescope for engine-specific compat issues
    - GE-Proton release notes for added fixes naming the game
    - PCGamingWiki <title> page, Linux section
    Report: (a) issue numbers + status, (b) any env var or
    VKD3D_CONFIG/DXVK_HUD workaround, (c) which proton version landed
    a fix. Under 300 words.

While agents run, optionally inspect the local proton log (PROTON_LOG=1 writes to ~/steam-<id>.log) for OBVIOUS errors. Don't form a theory yet — the research output reframes log lines.

Phase 3: Apply the Documented Fix

If research found a fix:

1. Apply it (launch option in Steam, env var in launch options, etc.)
2. Test it
3. If it works: DONE. Stop. Do not also "fix" the underlying shim.
4. If the fix is wired through nix-config (e.g., add it to pkgs/proton-gamescope/run.sh as a default), make the minimal change and commit with a comment citing the source thread / issue.

Phase 4: Only If Research Is Empty — Then Diagnose

Only after all six sources have been checked AND no documented fix exists, escalate to code-level diagnosis:

1. Reproduce with PROTON_LOG=1
2. Bisect the stack: try PROTON_USE_WAYLAND=0/1, gamescope on/off, different proton builds (proton-cachyos vs GE-Proton vs experimental)
3. Form a hypothesis WITH EVIDENCE from logs
4. Verify the hypothesis in the source before patching

If you reach this phase, hand off to gambit:debugging for the systematic root-cause process.

Critical Rules

Rules That Have No Exceptions

1. No shim patches before research — Research takes 30 minutes; patches take days.
2. The user wanting "the technical answer" is not permission to skip research — Confident technical briefs about NVAPI IDs / vkd3d swapchain races / NGX queries are exactly the trap this skill exists to prevent.
3. If the fix is /some-cli-flag or PROTON_FOO=1, that's the fix — Don't also patch the underlying behavior. Game ships with a launch option for a reason.
4. A "confident technical brief" is evidence of a trap, not evidence of correctness — When training data confidently names internal function IDs, structure fields, or closed-source behavior, treat that as a flag to check community sources HARDER, not as a green light to start patching.
5. 30-minute research time-box is a floor, not a ceiling — If 30 minutes turns up nothing, that's signal this might genuinely be a new bug; document and proceed to Phase 4. But don't shortcut research because "I bet it's the swapchain."

Common Excuses

All mean: STOP. Do the research first.

Reference: PRAGMATA Anti-Pattern

This skill exists because PRAGMATA (Steam app 3357650) was debugged for ~10 hours and produced 4 fork patches:

• dxvk-nvapi-josh: 5 Blackwell/Streamline NVAPI ID stubs + CUDA SM fix
• vkd3d-proton-josh: 0×0 ResizeBuffers refusal + maxImageExtent bail-out
• gamescope-patches/win-is-useless-respect-content-override
• gamescope-patches/scale-by-buffer-when-x11-geom-smaller

Every patch addressed a real bug — but none of them gated the user's goal (RT/PT/DLSS-RR enablement). The actual fix was:

• PROTON_USE_WAYLAND=1 (skip the X11 path that motivated the gamescope patches)
• PROTON_DLSS_UPGRADE=1 + don't hide NVIDIA GPU
• /WineDetectionEnabled:False as a game launch option

All three were findable in 15 minutes via this skill's checklist. None were inventable from first principles.

The forks were removed in nix-config commit 6251c4c. The branches are preserved on GitHub for historical reference. Do not repeat this pattern.

Verification Checklist

Before reporting a "fix" or making any code change to the Wine/Proton stack:

• Game title + Steam app ID identified
• Engine identified
• All six sources checked (or time-box elapsed)
• Documented fix from community: APPLIED + VERIFIED, or NONE FOUND
• If applying a documented fix: minimal change, commit references the source
• If no documented fix: handed off to gambit:debugging with research notes attached

Can't check all boxes? Return to Phase 2.

Integration

This skill calls:

• Two parallel general-purpose research agents (Phase 2)
• gambit:debugging (Phase 4, only if research is empty)

Called by:

• User reports a Steam game on Linux broken
• Before any commit that touches a Wine/Proton stack package
• Before opening a fork of any Wine/Proton/DXVK/vkd3d/gamescope project