setup-engine

When this skill is invoked:

!bash "${CLAUDE_SKILL_DIR}/../../hooks/yaml-helper.sh" resolve_config --keys workflow

Tier awareness. The workflow tier resolved above governs which design artifact this skill expects and the finish path it recommends in §12:

• minimal — the design artifact is the one-page design/game-brief.md (no GDDs, systems decomposition, or per-system design at this tier). /setup-engine runs first in the minimal path, so a missing brief here is normal, not a gap. The finish path is the 4-step floor.
• standard / full — the design artifact is design/gdd/game-concept.md and the finish path is the full pipeline.

If the block did not render (shell preprocessing disabled), assume standard.

1. Parse Arguments

Four modes:

• Full spec: /setup-engine godot 4.6 — engine and version provided
• Engine only: /setup-engine unity — engine provided, version will be looked up
• No args: /setup-engine — fully guided mode (engine recommendation + version)
• Refresh: /setup-engine refresh — update reference docs (see Section 10)
• Upgrade: /setup-engine upgrade [old-version] [new-version] — migrate to a new engine version (see Section 11)

2. Guided Mode (No Arguments)

If no engine is specified, run an interactive engine selection process:

Check for existing game concept

Read the design artifact for the resolved tier (see Tier awareness above):

• standard / full: read design/gdd/game-concept.md if it exists — extract genre, scope, platform targets, art style, team size, and any engine recommendation from /brainstorm.

• minimal: read design/game-brief.md if it exists — extract genre, scope, platform, and art direction from its fields. Its absence is expected at minimal (the brief is authored after engine setup in the minimal path), so do not treat a missing brief as a gap — proceed straight to guided selection.

• If no concept or brief exists, inform the user:

  "No game concept found. Consider running /brainstorm first to discover what you want to build — it will also recommend an engine. Or tell me about your game and I can help you pick."

  (At minimal this is optional, not a prerequisite — you can pick an engine now and write the brief next.)

If the user wants to pick without a concept, ask in this order:

Question 1 — Prior experience (ask this first, always, via AskUserQuestion):

• Prompt: "Have you worked in any of these engines before?"
• Options: Godot / Unity / Unreal Engine 5 / Multiple — I'll explain / None of them
• If they pick a specific engine → recommend that engine. Prior experience outweighs all other factors. Confirm with them and skip the matrix.
• If "None" or "Multiple" → continue to the questions below.

Questions 2-6 — Decision matrix inputs (only if no prior engine experience):

Question 2 — Target platform (ask this second, always, via AskUserQuestion — platform eliminates or heavily weights engines before any other factor):

• Prompt: "What platforms are you targeting for this game?"
• Options: PC (Steam / Epic) / Mobile (iOS / Android) / Console / Web / Browser / Multiple platforms
• Platform rules that feed directly into the recommendation:
  • Mobile → Unity strongly preferred; Unreal is a poor fit; Godot is viable for simple mobile
  • Console → Unity or Unreal; Godot console support requires third-party publishers or significant extra work
  • Web → Godot exports cleanly to web; Unity WebGL is functional; Unreal has poor web support
  • PC only → all engines viable; other factors decide
  • Multiple → Unity is the most portable across PC/mobile/console

1. What kind of game? (2D, 3D, or both?)
2. Primary input method? (keyboard/mouse, gamepad, touch, or mixed?)
3. Team size and experience? (solo beginner, solo experienced, small team?)
4. Any strong language preferences? (GDScript, C#, C++, visual scripting?)
5. Budget for engine licensing? (free only, or commercial licenses OK?)

Produce a recommendation

Do NOT use a simple scoring matrix that eliminates engines. Instead, reason through the user's profile against the honest tradeoffs below, then present 1-2 recommendations with full context. Always end with the user choosing — never force a verdict.

Engine honest tradeoffs:

Godot 4

• Genuine strengths: 2D (best in class), stylized/indie 3D, rapid iteration, free forever (MIT), open source, gentlest learning curve, best for solo devs who want full control
• Real limitations: 3D ecosystem is thin compared to Unity/Unreal (fewer tutorials, assets, community answers for 3D-specific problems); large open-world 3D is very hard and largely untested in Godot; console export requires third-party publishers or significant extra work; smaller professional job market
• Licensing reality: Truly free with no revenue thresholds ever. MIT license means you own everything.
• Best fit: 2D games of any scope; stylized/atmospheric 3D; contained 3D worlds (not open-world); first game projects where learning curve matters; projects where budget is a hard constraint at any scale

Unity

• Genuine strengths: Industry standard for mid-scope 3D and mobile; massive asset store and tutorial ecosystem; C# is a professional language; best console certification support for indie; strong community for almost every genre
• Real limitations: Licensing controversy in 2023 damaged trust (runtime fee was proposed then walked back — the risk of policy changes remains real); C# has a steeper initial curve than GDScript; heavier editor than Godot for simple projects
• Licensing reality: Free under $200K revenue AND 200K installs (Unity Personal/Plus). Only becomes costly if the game is genuinely successful — most indie games never hit this threshold. The 2023 controversy is worth knowing about but the actual current terms are reasonable for most indie developers.
• Best fit: Mobile games; mid-scope 3D; games targeting console; developers with C# background; projects needing large asset store; teams of 2-5

Unreal Engine 5

• Genuine strengths: Best-in-class 3D visuals (Lumen, Nanite, Chaos physics); industry standard for AAA and photorealistic 3D; large open-world support is mature and production-tested; Blueprint visual scripting lowers C++ barrier; strong for games targeting high-end PC or console
• Real limitations: Steepest learning curve; heaviest editor (slow compile times, large project sizes); overkill for stylized/2D/small-scope games; C++ is genuinely hard; not suitable for mobile or web; 5% royalty past $1M gross revenue
• Licensing reality: 5% royalty only applies AFTER $1M gross revenue per title. For a first game or any game that doesn't reach $1M, it costs nothing. This threshold is high enough that most indie developers will never pay it.
• Best fit: AAA-quality 3D; large open-world games; photorealistic visuals; developers with C++ experience or willing to use Blueprint; games targeting high-end PC/console where visual fidelity is a core selling point

Genre-specific guidance (factor this into the recommendation):

• 2D any style → Godot strongly preferred
• 3D stylized / atmospheric / contained world → Godot viable, Unity solid alternative
• 3D open world (large, seamless) → Unity or Unreal; Godot is not production-proven for this
• 3D photorealistic / AAA-quality → Unreal
• Mobile-first → Unity strongly preferred
• Console-first → Unity or Unreal; Godot console support requires extra work
• Horror / narrative / walking sim → any engine; match to art style and team experience
• Action RPG / Soulslike → Unity or Unreal for 3D; community support and assets matter here
• Platformer 2D → Godot
• Strategy / top-down / RTS → Godot or Unity depending on 2D vs 3D

Recommendation format:

1. Show a comparison table with the user's specific factors as rows
2. Give a primary recommendation with honest reasoning
3. Name the best alternative and when to choose it instead
4. Explicitly state: "This is a starting point, not a verdict — you can always migrate engines, and many developers switch between projects."
5. Use AskUserQuestion to confirm: "Does this recommendation feel right, or would you like to explore a different engine?"
   • Options: [Primary engine] (Recommended) / [Alternative engine] / [Third engine] / Explore further / Type something

If the user picks "Explore further": Use AskUserQuestion with concept-specific deep-dive topics. Always generate these options from the user's actual concept — do not use generic options. Always include at minimum:

• The primary engine's specific limitations for this concept (e.g., "How far can Godot 3D actually go for [genre]?")
• The alternative engine's specific tradeoffs for this concept
• Language choice impact on this concept's technical challenges
• Any concept-specific technical concern (e.g., adaptive audio, open-world streaming, multiplayer netcode)

The user can select multiple topics. Answer each selected topic in depth before returning to the engine confirmation question.

3. Look Up Current Version

Once the engine is chosen:

• If version was provided, use it
• If no version provided, use WebSearch to find the latest stable release:
  • Search: "[engine] latest stable version [current year]"
  • Confirm with the user: "The latest stable [engine] is [version]. Use this?"

Check the chosen version against what is actually installed

A version found by web search is what exists, not what the developer has. Pinning one they cannot run means every later instruction — build, test, smoke, the engine reference docs — targets an engine that is not on the machine.

Probe for the binary (Bash), and treat failure as unknown, never as absent:

Then:

• Match — say so in one line and continue.
• Mismatch — state both versions and ask, offering three options: pin the installed version, pin the newer one and upgrade later, or pin the newer one deliberately. Record the answer; do not pick silently.
• Not found / probe failed — report installed version NOT DETERMINED and continue with the chosen version. Do not report this as "no engine installed": a probe that could not run has not established absence.

Whatever the outcome, write it into Section 7's VERSION.md as an Installed at pin time row, so a later reader can tell a deliberate version-ahead pin from an accident.

4. Update CLAUDE.md Technology Stack

Language Selection (Godot only)

If Godot was chosen, ask the user which language to use before showing the proposed Technology Stack:

"Godot supports two primary languages:

A) GDScript — Python-like, Godot-native, fastest iteration. Best for beginners, solo devs, and teams coming from Python or Lua. B) C# — .NET 8+, familiar to Unity developers, stronger IDE tooling (Rider / Visual Studio), slight performance advantage on heavy logic. C) Both — GDScript for gameplay/UI scripting, C# for performance-critical systems. Advanced setup — requires .NET SDK alongside Godot.

Which will this project primarily use?"

Record the choice. It determines the CLAUDE.md template, naming conventions, specialist routing, and which agent is spawned for code files throughout the project.

Read CLAUDE.md and show the user the proposed Technology Stack changes. Ask: "May I write these engine settings to CLAUDE.md?"

Wait for confirmation before making any edits.

Update the Technology Stack section, replacing the [CHOOSE] placeholders with the actual values:

For Godot — use the template matching the language chosen above. See .claude/skills/setup-engine/references/godot-language-config.md (A1) for all three variants (GDScript, C#, Both).

For Unity:

- **Engine**: Unity [version]
- **Language**: C#
- **Build System**: Unity Build Pipeline
- **Asset Pipeline**: Unity Asset Import Pipeline + Addressables

For Unreal:

- **Engine**: Unreal Engine [version]
- **Language**: C++ (primary), Blueprint (gameplay prototyping)
- **Build System**: Unreal Build Tool (UBT)
- **Asset Pipeline**: Unreal Content Pipeline

Engine reference import

In the same CLAUDE.md write, set the Engine Version Reference import to the chosen engine. Find the line marked ENGINE-REFERENCE-IMPORT (an @docs/engine-reference/<engine>/VERSION.md line under its comment) and Edit it to point at the configured engine:

• Godot → @docs/engine-reference/godot/VERSION.md
• Unity → @docs/engine-reference/unity/VERSION.md
• Unreal → @docs/engine-reference/unreal/VERSION.md

This is why a fresh Unity or Unreal project no longer loads the Godot reference in every session. It is idempotent — re-running /setup-engine for a different engine rewrites the same line. (The target docs/engine-reference/<engine>/ directory is created in Section 8 below if it does not yet exist.)

5. Populate Technical Preferences

After updating CLAUDE.md, create or update .claude/docs/technical-preferences.md with engine-appropriate defaults. Read the existing template first, then fill in:

Engine & Language Section

• Fill from the engine choice made in step 4

Naming Conventions (engine defaults)

For Godot — see .claude/skills/setup-engine/references/godot-language-config.md (A2) for GDScript, C#, and Both variants.

For Unity (C#):

• Classes: PascalCase (e.g., PlayerController)
• Public fields/properties: PascalCase (e.g., MoveSpeed)
• Private fields: _camelCase (e.g., _moveSpeed)
• Methods: PascalCase (e.g., TakeDamage())
• Files: PascalCase matching class (e.g., PlayerController.cs)
• Constants: PascalCase or UPPER_SNAKE_CASE

For Unreal (C++):

• Classes: Prefixed PascalCase (A for Actor, U for UObject, F for struct)
• Variables: PascalCase (e.g., MoveSpeed)
• Functions: PascalCase (e.g., TakeDamage())
• Booleans: b prefix (e.g., bIsAlive)
• Files: Match class without prefix (e.g., PlayerController.h)

Input & Platform Section

Populate ## Input & Platform using the answers gathered in Section 2 (or extracted from the game concept). Derive the values using this mapping:

For Primary Input, use the dominant input for the game genre:

• Action/RPG/platformer targeting console → Gamepad
• Strategy/point-and-click/RTS → Keyboard/Mouse
• Mobile game → Touch
• Cross-platform → ask the user

Genre may not exist yet — check before deriving from it. At minimal the design artifact is design/game-brief.md, and it is authored after this skill runs (Section 2 says so explicitly). There is no genre to map. The same is true at any tier when /setup-engine is run before the concept exists.

When genre is unavailable, ask — do not infer one from the platform, and do not leave the field silently blank:

• Prompt: "Primary input for a [2D/3D] [platform] game? Genre isn't established yet — the brief comes next — so this can't be derived."
• Options: the plausible inputs for that platform, plus Leave as [TO BE CONFIGURED] — a legitimate answer here, revisited via /settings once the brief exists.

Gamepad Support and Touch Support still come from the platform table above; only Primary Input depends on genre.

Present the derived values and ask the user to confirm or adjust before writing.

Example filled section:

## Input & Platform
- **Target Platforms**: PC, Console
- **Input Methods**: Keyboard/Mouse, Gamepad
- **Primary Input**: Gamepad
- **Gamepad Support**: Full
- **Touch Support**: None
- **Platform Notes**: All UI must support d-pad navigation. No hover-only interactions.

Remaining Sections

• Performance Budgets: Use AskUserQuestion:
  • Prompt: "Should I set default performance budgets now, or leave them for later?"
  • Options: [A] Set defaults now (60fps, 16.6ms frame budget, engine-appropriate draw call limit) / [B] Leave as [TO BE CONFIGURED] — I'll set these when I know my target hardware
  • If [A]: populate with the suggested defaults. If [B]: leave as placeholder.
• Testing: Suggest the engine-appropriate framework — gdUnit4 for Godot, NUnit for Unity, Automation Spec for Unreal — and ask before adding.

  Must match commands.test in Section 5.5.1, which writes godot --headless --script tests/gdunit4_runner.gd, and .claude/docs/coding-standards.md, which names the same runner. Naming GUT here would have the skill recommend one framework and configure another in the same run.

• Forbidden Patterns: Leave as placeholder — do NOT pre-populate.
• Allowed Libraries: Leave as placeholder — do NOT pre-populate dependencies the project does not currently need. Only add a library here when it is actively being integrated, not speculatively.

Guardrail: Never add speculative dependencies to Allowed Libraries. For example, do NOT add GodotSteam unless Steam integration is actively beginning in this session. Post-launch integrations should be added to Allowed Libraries when that work begins, not during engine setup.

Engine Specialists Routing

Also populate the ## Engine Specialists section in technical-preferences.md with the correct routing for the chosen engine:

For Godot — see .claude/skills/setup-engine/references/godot-language-config.md (A3) for the routing table matching the language chosen.

For Unity:

## Engine Specialists
- **Primary**: unity-specialist
- **Language/Code Specialist**: unity-specialist (C# review — primary covers it)
- **Shader Specialist**: unity-shader-specialist (Shader Graph, HLSL, URP/HDRP materials)
- **UI Specialist**: unity-ui-specialist (UI Toolkit UXML/USS, UGUI Canvas, runtime UI)
- **Additional Specialists**: unity-dots-specialist (ECS, Jobs system, Burst compiler), unity-addressables-specialist (asset loading, memory management, content catalogs)
- **Routing Notes**: Invoke primary for architecture and general C# code review. Invoke DOTS specialist for any ECS/Jobs/Burst code. Invoke shader specialist for rendering and visual effects. Invoke UI specialist for all interface implementation. Invoke Addressables specialist for asset management systems.

### File Extension Routing

| File Extension / Type | Specialist to Spawn |
|-----------------------|---------------------|
| Game code (.cs files) | unity-specialist |
| Shader / material files (.shader, .shadergraph, .mat) | unity-shader-specialist |
| UI / screen files (.uxml, .uss, Canvas prefabs) | unity-ui-specialist |
| Scene / prefab / level files (.unity, .prefab) | unity-specialist |
| Native extension / plugin files (.dll, native plugins) | unity-specialist |
| General architecture review | unity-specialist |

For Unreal:

## Engine Specialists
- **Primary**: unreal-specialist
- **Language/Code Specialist**: ue-blueprint-specialist (Blueprint graphs) or unreal-specialist (C++)
- **Shader Specialist**: unreal-specialist (no dedicated shader specialist — primary covers materials)
- **UI Specialist**: ue-umg-specialist (UMG widgets, CommonUI, input routing, widget styling)
- **Additional Specialists**: ue-gas-specialist (Gameplay Ability System, attributes, gameplay effects), ue-replication-specialist (property replication, RPCs, client prediction, netcode)
- **Routing Notes**: Invoke primary for C++ architecture and broad engine decisions. Invoke Blueprint specialist for Blueprint graph architecture and BP/C++ boundary design. Invoke GAS specialist for all ability and attribute code. Invoke replication specialist for any multiplayer or networked systems. Invoke UMG specialist for all UI implementation.

### File Extension Routing

| File Extension / Type | Specialist to Spawn |
|-----------------------|---------------------|
| Game code (.cpp, .h files) | unreal-specialist |
| Shader / material files (.usf, .ush, Material assets) | unreal-specialist |
| UI / screen files (.umg, UMG Widget Blueprints) | ue-umg-specialist |
| Scene / prefab / level files (.umap, .uasset) | unreal-specialist |
| Native extension / plugin files (Plugin .uplugin, modules) | unreal-specialist |
| Blueprint graphs (.uasset BP classes) | ue-blueprint-specialist |
| General architecture review | unreal-specialist |

Collaborative Step

Present the filled-in preferences to the user. For Godot, include the chosen language and note where the full naming conventions and routing tables live:

"Here are the default technical preferences for [engine] ([language if Godot]). The naming conventions and specialist routing are in this skill's references directory — I'll apply the [GDScript/C#/Both] variant. Want to customize any of these, or shall I save the defaults?"

For all other engines, present the defaults directly without referencing the appendix.

Wait for approval before writing the file.

5.5 Populate project.yaml (Primary Config Store)

v1.1: project.yaml at the repo root is the primary store for project configuration. The .claude/docs/technical-preferences.md file written in Section 5 is kept as a legacy mirror for backward compatibility. This step is a dual-write — the same engine facts go into both files, and project.yaml wins when a skill reads a key present in both.

After technical-preferences.md is written and approved, dual-write the structured config into project.yaml. Four blocks are written: engine, specialists, naming, and commands.

5.5.1 Build the four blocks

Derive every value from the engine and language already chosen in Sections 3–4. Do NOT re-ask for the engine, version or language — reuse those decisions.

That is not a blanket "never ask". rendering and physics below depend on two further inputs — target platform and 2D-vs-3D — which Section 2 collects on only one of the four entry paths. When they were never collected, ask; the unavailable-branch under the project-shape table says how.

engine block:

engine:
  name: "<Godot|Unity|Unreal>"
  version: "<version from Section 3>"
  language: "<GDScript|C#|C++|Blueprint>"
  rendering: "<engine default — see table>"
  physics: "<engine default — see table>"

On Godot these two values depend on the answers Section 2 already collected — the target platform and 2D-vs-3D — so do not pick them from the engine name alone. On Unity and Unreal the table has a single any row and the engine name is sufficient; take those rows directly.

Why this table has a shape column and the others do not. Both Godot defaults were wrong for a 2D browser game, and both were wrong from data this skill had already collected and then discarded.

• Jolt is Godot's default 3D engine. docs/engine-reference/godot/modules/physics.md: "Jolt Physics is the DEFAULT 3D engine" and "2D physics UNCHANGED (still Godot Physics 2D)". Writing Jolt on a 2D project sends the implementer to tune a backend their game does not use.
• Forward+ is desktop-focused. docs/engine-reference/godot/modules/rendering.md: Forward+ is "Full featured, desktop-focused"; Compatibility is "OpenGL 3.3 / WebGL 2, broadest hardware support" — the browser path.

If Section 2's platform answer was Multiple platforms including web, use the web row: the renderer must work everywhere the game ships.

Godot only — Unity and Unreal have one row each, keyed any. Shape cannot change rendering or physics for those two, so do not run the resolution below for them: asking an operator a question whose answer you will discard is exactly what §5.5.1 opens by forbidding. On Unity write URP/PhysX and on Unreal write Lumen + Nanite (deferred)/Chaos straight from the table.

Section 2 did not necessarily run — check before reading its answers. Target platform and 2D-vs-3D are collected under Questions 2–6, only if no prior engine experience. Three of the four entry paths never reach them: /setup-engine <engine> <version> and /setup-engine <engine> skip Section 2 outright, and guided mode skips the matrix as soon as the user names an engine they have worked in before. Only guided mode answered None or Multiple collects both.

Resolve each input in this order and stop at the first that answers:

1. Section 2's answers, if that path ran.
2. The design artifact — design/gdd/game-concept.md at standard/full, design/game-brief.md at minimal. Section 2 already extracts platform targets from these; extract 2D-vs-3D the same way when it is stated.
3. Ask. Do not infer the shape from the engine name, and do not write a row you could not justify:
   • Prompt: "rendering and physics depend on the project's shape, which hasn't been established yet. Is this 2D or 3D, and does it ship to web?"
   • Options: 2D · non-web / 2D · web / 3D · non-web / 3D · web, plus Leave as [TO BE CONFIGURED] — a legitimate answer here, revisited via /settings once the concept exists.

[TO BE CONFIGURED] is a valid value for both keys. A wrong Jolt on a 2D project is worse than an unset one, because nothing downstream questions it.

• rendering and physics are engine-typical defaults — tell the user they can be changed later via /settings if the project uses a different setup.
• For Godot Both, write language: "GDScript" (the primary gameplay language); the C# usage is recorded in technical-preferences.md.
• For Unreal, write language: "C++" — or "Blueprint" only if the project is Blueprint-primary. Blueprint as a secondary tool does not change this value.

specialists block — copy directly from the routing table chosen in Section 5 (A3 in .claude/skills/setup-engine/references/godot-language-config.md for Godot):

specialists:
  code: "<code specialist>"
  shader: "<shader specialist>"
  ui: "<ui specialist>"
  additional: ["<...>"]

naming block — enum values (NOT the prose form used in technical-preferences.md). Use the column matching the engine and, for Godot, the language:

The Unreal column is sourced, not inherited from the table's generic shape. variables: camelCase and signals: on_event_name are the two rows that shape would produce, and both are wrong for Unreal. Checked against this repo's pinned reference: docs/engine-reference/unreal/ contains zero camelCase variable declarations and uses PascalCase throughout (int32 Health;, FVector ServerPosition;), and the word "signal" never appears in it at all — it is Godot vocabulary. Unreal has delegates and events, and the reference's handlers are PascalCase On<Event>.

Two caveats kept rather than smoothed over. (1) classes: PascalCase is incomplete for Unreal, not wrong: UE requires a mandatory type prefix (U/A/F/E/I/T) that this enum cannot express, so an Unreal project's coding standards must state it separately. (2) scenes is a category mismatch — Unreal has Levels and Maps under World Partition, not scenes — left in place because the key is shared across engines and renaming it is a schema change, not a value fix.

The blast radius is limited: naming.* is currently a documented-but-unread setting, so wrong values misinform a human reading project.yaml rather than driving any automated check — today. That is a reason to get them right now, while it is cheap.

Three further rules for this table.

The Unity build row must not hardcode -buildTarget StandaloneLinux64. A hardcoded target gives every Unity project a Linux build command, whatever platform it actually ships on. The row reads <TARGET>: ask the operator for the build target and write the value they give. The correct -buildTarget identifiers are not sourceable from docs/engine-reference/unity/, so this skill must not emit one from recall — the same call made for /security-audit's save patterns and for Unity's release dates. A wrong-but-plausible default is worse than an explicit question: it produces a commands.build that runs, succeeds, and builds the wrong artifact.

The Godot build row must not hardcode 'Linux/X11' either — same defect, same remedy. A Godot export preset name is project-defined: it is whatever string the operator typed into export_presets.cfg, and the shipped defaults are per-platform (Windows Desktop, macOS, Web, Linux/X11). Writing 'Linux/X11' gives a Windows-targeting project a build command that fails with Unknown export preset, and gives a project that does have a Linux preset a command that silently builds the wrong platform. The row reads <PRESET>: ask the operator which export preset to build and write the value they give, exactly as the Unity row does. If no presets exist yet — common, since /setup-engine usually runs before the Godot project has any — write [TO BE CONFIGURED] and say so, rather than guessing a name that does not exist.

The constants row must not contradict this skill's own prose. The table says SCREAMING_SNAKE for Unity; the Unity section of this same file says "Constants: PascalCase or UPPER_SNAKE_CASE". Both cannot be authoritative, and an agent following one produces config the other rejects. The row is left unchanged pending sourcing rather than picked by preference — neither docs/engine-reference/unity/ nor unreal/ contains a SCREAMING_SNAKE constant to confirm or refute it, and the Unreal run flagged the same row as wrong for Unreal on the same grounds. Resolve by adding a naming section to the engine references, then correct table and prose together. Until then, treat naming.constants as unverified for Unity and Unreal.

Write that caveat into project.yaml, do not leave it here. On Unity and Unreal, emit the constants line with a trailing comment:

naming:
  constants: SCREAMING_SNAKE   # UNVERIFIED — not sourceable from
                               # docs/engine-reference/<engine>/; confirm before relying on it

Without it, a value the skill knows is unsourced is recorded as flatly as classes: PascalCase, which is sourced, and the reader of the primary config store cannot tell them apart. The commands block nine lines below already does exactly this with its # TODO: confirm these line — this is the same pattern, applied to the value that needs it just as much.

For Godot Both, use the GDScript column — .gd files dominate gameplay scripting; .cs files follow C# conventions per-file (see A2 in .claude/skills/setup-engine/references/godot-language-config.md).

naming:
  classes: <value>
  variables: <value>
  constants: <value>
  signals: <value>
  files: <value>
  scenes: <value>

commands block — engine-default shell commands, simple-string form:

commands.run is the one the run-and-observe step depends on. It must launch the game, windowed, at a fixed resolution — never the editor, and never with a headless / batch / null-RHI flag, which exist to skip rendering. /dev-story Phase 6 step 4 appends the per-engine capture flags to it (.claude/docs/run-and-observe.md). test and smoke feed the parse check and /smoke-check; build is the one row you must ask for.

YAML quoting rule — applies to EVERY command value. yaml-helper.sh — the parser every config read in this framework goes through — decodes no escape sequences: neither \" inside a double-quoted scalar nor '' inside a single-quoted scalar. It takes the first matching quote character as the end of the value and discards the rest, so "he said \"hi\" now" parses as he said \. Verified against the parser, not inferred. The rule is preventative here — it applies the moment anything does read commands.*, and to every other quoted value in project.yaml today. Pick the quote style that needs no escaping:

• value contains a single quote ' (e.g. the Godot build above) → wrap it in a double-quoted YAML scalar: "... 'Linux/X11' ..."
• value contains a double quote " (e.g. the Unreal test/smoke below) → wrap it in a single-quoted YAML scalar: '... "Quit" ...'
• value contains neither → use a double-quoted scalar for consistency. Never use a quote style that forces an escape (\" or '') — the parser truncates the value at the escape. A value containing BOTH quote types cannot be represented for this parser; rewrite the command to drop one.

Godot / Unity — write the table values directly, substituting the operator's answer for <PRESET> / <TARGET>. Godot's build contains a single quote, so it takes a double-quoted scalar (Windows Desktop below is the example answer, not a default — write what the operator said):

commands:
  build: "godot --headless --export-debug 'Windows Desktop'"
  test: "godot --headless --script tests/gdunit4_runner.gd"
  run: "godot --path . --windowed --resolution 1280x720"
  smoke: "godot --headless --quit-after 5"

Also write engine.path if the editor is not on PATH. These commands name the executable bare, which assumes it resolves — and on Windows none of the three engines installs onto PATH by default. Ask for or probe the install location and record it:

engine:
  path: "C:/Program Files/Epic Games/UE_5.7"   # omit if the editor is on PATH

This is not cosmetic. Without it, an agent reports "no editor on this machine" and ships C++ it never compiled — on a machine where that engine WAS installed. Nothing in the project told it where to look, so absence of a path read as absence of an engine.

For Unreal, UE build/test commands vary by version and project setup. Write best-effort values and add a # TODO comment so the user knows to confirm them. The test/smoke commands embed double quotes, so they take single-quoted scalars:

commands:
  # TODO: confirm these for your UE version and project — adjust via /settings
  build: 'RunUAT.bat BuildCookRun -project=<project>.uproject -platform=Win64 -build -cook'
  test: 'UnrealEditor-Cmd.exe <project>.uproject -ExecCmds="Automation RunTests <project>; Quit" -unattended -nullrhi'
  run: 'UnrealEditor.exe <project>.uproject -game -windowed -ResX=1280 -ResY=720'
  smoke: 'UnrealEditor-Cmd.exe <project>.uproject -game -nullrhi -unattended -ExecCmds="Quit"'

Two details are load-bearing. smoke needs -game: without it UnrealEditor-Cmd boots the editor, where a bare Quit console command only ends a play-in-editor session — the process stays resident and the command never returns; with -game the same line boots headless and exits in seconds. test needs the ; Quit inside the Automation string: the automation runner handles that trailing Quit itself and exits the editor once the tests finish, and without it the run also never returns.

5.5.2 Write the blocks to project.yaml

Show the user the full set of four blocks and ask:

"May I write the engine, specialists, naming, and commands blocks to project.yaml?"

Wait for confirmation, then apply based on the file's current state:

• project.yaml does not exist — create it with the Write tool using this v1.1 template (the four blocks appended after framework; replace <...> and the date):

  # CCGS project configuration — single source of truth for project settings.
  # Schema: grep the `## <key>` section of .claude/docs/effects-map.md —
  # it is ~31k tokens whole, ~900 per section. Do not open it entire.
  
  schema_version: 1
  
  framework:
    version: 1.1.1
    last_upgraded: <today's date>
  
  engine:
    name: "<...>"
    version: "<...>"
    language: "<...>"
    rendering: "<...>"
    physics: "<...>"
  
  specialists:
    code: "<...>"
    shader: "<...>"
    ui: "<...>"
    additional: ["<...>"]
  
  naming:
    classes: <...>
    variables: <...>
    constants: <...>
    signals: <...>
    files: <...>
    scenes: <...>
  
  commands:
    build: "<...>"
    test: "<...>"
    run: "<...>"
    smoke: "<...>"
  

  Do not seed modes.review_mode here. It is a rigor-fronted knob — modes.rigor supplies its value, so an explicit value would shadow the rigor expansion and pin the review mode regardless of the project's rigor. Test Y.6 locks this in.

• project.yaml exists — Read it first (the Edit tool requires the file to have been read this session), then, processing the blocks in the order engine → specialists → naming → commands, for each block:

  • Block absent — insert the whole block, appended after the last existing top-level block.
  • Block already present (a re-run of /setup-engine) — Edit the existing keys in place, and add any keys the block is missing (a partial block must end up with its full key set). Do NOT add a second copy of the block.

Preserve all other content in project.yaml (schema_version, framework, modes, project, etc.) — only the four blocks are touched.

5.5.3 Verify the dual-write

Read project.yaml back and confirm the four blocks are present and that engine.name, engine.language, and the naming values match what was written to technical-preferences.md. If they diverge, report the discrepancy to the user and stop — a split config corrupts skill and hook reads.

6. Determine Knowledge Gap

Check whether the engine version is likely beyond the LLM's training data.

Known approximate coverage — last re-checked 2026-08-28:

• LLM knowledge cutoff: May 2026
• Godot: training data likely covers up to ~4.6
• Unity: training data likely covers up to ~6000.x
• Unreal: training data likely covers up to ~5.5

This table goes stale silently, and a stale table fails in the dangerous direction only if it is too new. A cutoff left unchanged for a year after it stopped being true over-classifies risk — safe, but every project then pays for full reference docs it may not have needed. The opposite error is the harmful one: a cutoff claimed later than the model's actual one marks post-cutoff versions LOW RISK and suppresses the reference docs that exist to stop invented APIs.

If the date above is more than six months old, do not trust it. Say so, and treat the engine version as HIGH RISK regardless of the comparison — an unverifiable cutoff is not a cutoff that was met.

Compare the user's chosen version against these baselines:

• Within training data → LOW RISK — reference docs optional but recommended
• Near the edge → MEDIUM RISK — reference docs recommended
• Beyond training data → HIGH RISK — reference docs required

Inform the user which category they're in and why.

7. Populate Engine Reference Docs

First: does a reference set already exist for this engine?

Check before doing anything else. The template ships docs/engine-reference/godot/, unity/ and unreal/ already populated, so "the directory exists and pins a version" is the state of every fresh project, not an edge case. Both branches below say "create", and following either one literally on a pre-populated directory either overwrites curated content or leaves project.yaml and the CLAUDE.md-imported reference disagreeing.

Read docs/engine-reference/<engine>/VERSION.md and compare its Engine Version to the version chosen in Section 3:

• No directory, or no VERSION.md → create, using the risk branch below.
• Same version → nothing to do. Refresh Last Docs Verified only if you actually re-verified against the docs this run. Do not restamp a date you did not check.
• Directory pins an OLDER version than the one chosen → update, do not replace. This is the common case.
  1. Edit VERSION.md in place: new Engine Version, new Project Pinned and Last Docs Verified, the Installed at pin time row from Section 3, and a new row in the post-cutoff timeline for each version added.
  2. Append to breaking-changes.md, deprecated-apis.md and current-best-practices.md under a heading naming the version span (## 4.6 → 4.7). Never truncate the older spans — a project migrating across two versions still needs the earlier one.
  3. Re-grade the older timeline rows if the cutoff moved past them.
• Directory pins a NEWER version than the one chosen → stop and ask. Someone pinned forward deliberately, or the version choice is wrong. Do not silently downgrade a curated reference.

Sourcing rule for everything written in this section

Never fill a gap from training data. Write the gap down instead.

The whole purpose of these files is to be the thing agents consult instead of their training data. A confidently wrong entry here is worse than no entry: it produces work that looks verified and is not.

• Every claim must come from a page you fetched this run. Record the URL.
• If the official docs do not state something the template asks for — a release date, a subsystem's behaviour, web-export specifics — write NOT SOURCEABLE — <what>, not stated at <url> and move on.
• A NOT SOURCEABLE line is a successful outcome, not a failure to finish.
• Do not infer one fact from an adjacent one. "The migration guide lists no physics change" is not "the physics default is unchanged"; if you record the inference, label it as an inference and name what it rests on.

If WITHIN training data (LOW RISK):

Create a minimal docs/engine-reference/<engine>/VERSION.md:

# [Engine] — Version Reference

| Field | Value |
|-------|-------|
| **Engine Version** | [version] |
| **Project Pinned** | [today's date] |
| **LLM Knowledge Cutoff** | May 2025 |
| **Risk Level** | LOW — version is within LLM training data |

## Note

This engine version is within the LLM's training data. Engine reference
docs are optional but can be added later if agents suggest incorrect APIs.

Run `/setup-engine refresh` to populate full reference docs at any time.

Do NOT create breaking-changes.md, deprecated-apis.md, etc. — they would add context cost with minimal value.

If BEYOND training data (MEDIUM or HIGH RISK):

Create the full reference doc set by searching the web:

1. Search for the official migration/upgrade guide:

   • "[engine] [old version] to [new version] migration guide"
   • "[engine] [version] breaking changes"
   • "[engine] [version] changelog"
   • "[engine] [version] deprecated API"

2. Fetch and extract from official documentation:

   • Breaking changes between each version from the training cutoff to current
   • Deprecated APIs with replacements
   • New features and best practices

Ask: "May I create the engine reference docs under docs/engine-reference/<engine>/?"

Wait for confirmation before writing any files.

3. Create the full reference directory:

   docs/engine-reference/<engine>/
   ├── VERSION.md              # Version pin + knowledge gap analysis
   ├── breaking-changes.md     # Version-by-version breaking changes
   ├── deprecated-apis.md      # "Don't use X → Use Y" tables
   ├── current-best-practices.md  # New practices since training cutoff
   └── modules/                # Per-subsystem references (create as needed)
   

4. Populate each file using real data from the web searches, following the format established in existing reference docs. Every file must have a "Last verified: [date]" header.

5. For module files: Only create modules for subsystems where significant changes occurred. Don't create empty or minimal module files.

7.5 Scaffold the Engine Project

Without this step the framework produces source files no engine can open. /dev-story writes .gd/.cs/.cpp under the resolved code root, and the minimal path advertises "four steps to running code" — but nothing anywhere created a project for the engine to load. Verified by grep across every skill: no project.godot, no Unity project, no .uproject was ever written. The files were real and orphaned.

Godot — write project.godot if one is absent

Never overwrite an existing project.godot. If the file is already there, say so and skip to Section 8 — the developer has a project and its settings are theirs.

Show the proposed file, then ask: "May I create project.godot at the repo root?" On approval, write:

config_version=5

[application]

config/name="<project name>"
config/features=PackedStringArray("<major.minor>", "<renderer feature>")

[rendering]

renderer/rendering_method="<rendering method>"

Fill it from decisions already made — do not ask again:

Leave run/main_scene unset. There is no scene yet at engine-setup time. Add a comment saying /dev-story or the developer sets it once a scene exists; an empty project with no main scene opens fine in the editor.

Then verify, and report what the verification actually was. If the engine binary was found in Section 3, run its headless import (godot --headless --path . --import) and report the result. If the binary was not found, or its version differs from the pinned one, write project.godot NOT VERIFIED — <reason>. The config_version and feature strings are stable across Godot 4.x, but "stable in the versions I know" is not the same as "checked against the version you pinned", and only the run establishes the latter.

Unity and Unreal — instruct, do not fabricate

A Unity project and an .uproject are editor-generated and span many files, several of them binary or machine-specific. This repo cannot source their correct contents, and a hand-written scaffold would be the exact failure Section 7's sourcing rule forbids — something that looks finished and is quietly wrong.

Tell the user, in one short block, that CCGS does not create the project for these engines and they should create it first:

• Unity — create the project in Unity Hub at the repo root, choosing the template matching the 2D/3D answer from Section 2, then re-run /setup-engine.
• Unreal — create the project in the Epic launcher or via UnrealEditor, then re-run.

Report the outcome in the Section 12 summary either way — created, already present, or "not created, engine requires the editor" — so the user leaves this skill knowing whether a runnable project exists.

Deliberately not a project.yaml key. An engine.project_scaffolded flag would be written here and read by nothing, which is a dead setting — the same writer-without-reader defect the config gates exist to catch. The filesystem is the source of truth: any skill that needs to know globs for project.godot, *.uproject, or ProjectSettings/ProjectVersion.txt.

8. Verify the CLAUDE.md Import

This import was already written in Section 4 — do not edit it again and do not ask again. Section 4 sets it as part of the same CLAUDE.md write, anchored to the ENGINE-REFERENCE-IMPORT marker. This step only confirms the result.

Read CLAUDE.md and confirm the line under the marker reads:

@docs/engine-reference/<engine>/VERSION.md

with <engine> the engine just configured. If it still points at a different engine, Section 4 did not complete — go back and finish it rather than patching the line here.

Why this is a check and not a second write. Repeating the edit here with its own approval prompt would ask the user twice for one change, and the second ask would be for work already done. Locate the line by its marker, never by the ## Engine Version Reference heading — the marker exists precisely so the line can still be found when the heading moves or is reworded.

8.5 Read Back What You Just Wrote

This section exists because prose did not hold. Section 5.5.1's rendering/physics table already carries an emphatic, source-cited warning naming the two mistakes most often made here -- and it is still entirely possible to make both of them anyway, writing Forward+ and Jolt for a 2D browser game. Section 3's Installed at pin time row is just as easy to drop silently, because a missing row leaves no trace.

Neither is fixed by adding more instructions. They are fixed by verifying the files after writing them:

bash .claude/scripts/project-coherence.sh

It compares project.yaml against docs/engine-reference/<engine>/VERSION.md, against project.godot, and against the engine binary actually on PATH, and it checks that the files commands.build and commands.test name exist.

Report every [DIFFERS] line to the user and resolve it before finishing. Each one means two files this skill just wrote disagree, or describe something that is not there.

[NOT CHECKED] is not a pass. Each such line names why a comparison could not be made -- an absent binary, a missing project.godot. Say which ones applied. A comparison that could not run has not established agreement.

The script emits observations and never a verdict, per the convention in CLAUDE.md. The judgement is yours and the user's.

9. Update Agent Instructions

Ask: "May I add a Version Awareness section to the engine specialist agent files?" before making any edits.

For the chosen engine's specialist agents, verify they have a "Version Awareness" section. If not, add one following the pattern in the existing Godot specialist agents.

The section should instruct the agent to:

1. Read docs/engine-reference/<engine>/VERSION.md
2. Check deprecated APIs before suggesting code
3. Check breaking changes for relevant version transitions
4. Use WebSearch to verify uncertain APIs

10. Refresh Subcommand

If invoked as /setup-engine refresh:

1. Read the existing docs/engine-reference/<engine>/VERSION.md to get the current engine and version
2. Use WebSearch to check for:
   • New engine releases since last verification
   • Updated migration guides
   • Newly deprecated APIs
3. Update all reference docs with new findings
4. Update "Last verified" dates on all modified files
5. Report what changed

11. Upgrade Subcommand

If invoked as /setup-engine upgrade [old-version] [new-version]:

Step 1 — Read Current Version State

Read docs/engine-reference/<engine>/VERSION.md to confirm the current pinned version, risk level, and any migration note URLs already recorded. If old-version was not provided as an argument, use the pinned version from this file.

Step 2 — Fetch Migration Guide

Use WebSearch and WebFetch to locate the official migration guide between old-version and new-version:

• Search: "[engine] [old-version] to [new-version] migration guide"
• Search: "[engine] [new-version] breaking changes changelog"
• Fetch the migration guide URL from VERSION.md if one is already recorded, or use the URL found via search.

Extract: renamed APIs, removed APIs, changed defaults, behavior changes, and any "must migrate" items.

Step 3 — Pre-Upgrade Audit

Scan the code root (resolve per .claude/docs/code-root-resolution.md) for code that uses APIs known to be deprecated or changed in the target version:

• Use Grep to search for deprecated API names extracted from the migration guide (e.g., old function names, removed node types, changed property names)
• List each file that matches, with the specific API reference found

Present the audit results as a table:

Pre-Upgrade Audit: [engine] [old-version] → [new-version]
==========================================================

Files requiring changes:
  File                              | Deprecated API Found       | Effort
  --------------------------------- | -------------------------- | ------
  src/gameplay/player_movement.gd   | old_api_name               | Low
  src/ui/hud.gd                     | removed_node_type          | Medium

Breaking changes to watch for:
  - [change description from migration guide]
  - [change description from migration guide]

Recommended migration order (dependency-sorted):
  1. [system/layer with fewest dependencies first]
  2. [next system]
  ...

If no deprecated APIs are found in the code root, report: "No deprecated API usage found in the code root — upgrade may be low-risk."

Step 4 — Confirm Before Updating

Ask the user before making any changes:

"Pre-upgrade audit complete. Found [N] files using deprecated APIs. Proceed with upgrading VERSION.md to [new-version]? (This will update the pinned version and add migration notes — it does NOT change any source files. Source migration is done manually or via stories.)"

Wait for explicit confirmation before continuing.

Step 5 — Update VERSION.md

After confirmation:

1. Update docs/engine-reference/<engine>/VERSION.md:

   • Engine Version → [new-version]
   • Project Pinned → today's date
   • Last Docs Verified → today's date
   • Re-evaluate and update the Risk Level and Post-Cutoff Version Timeline table if the new version falls beyond the LLM knowledge cutoff
   • Add a ## Migration Notes — [old-version] → [new-version] section containing: migration guide URL, key breaking changes, deprecated APIs found in this project, and recommended migration order from the audit

2. If breaking-changes.md or deprecated-apis.md exist in the engine reference directory, append the new version's changes to those files.

3. If project.yaml exists at the repo root and has an engine block, Read it first, then update engine.version to [new-version] so the primary config store stays in sync with VERSION.md.

Step 6 — Post-Upgrade Reminder

After updating VERSION.md, output:

VERSION.md updated: [engine] [old-version] → [new-version]

Next steps:
1. Migrate deprecated API usages in the [N] files listed above
2. Run /setup-engine refresh after upgrading the actual engine binary to
   verify no new deprecations were missed
3. Run /architecture-review — the engine upgrade may invalidate ADRs that
   reference specific APIs or engine capabilities
4. If any ADRs are invalidated, run /propagate-design-change to update
   downstream stories

12. Output Summary

After setup is complete, output:

Engine Setup Complete
=====================
Engine:          [name] [version]
Language:        [GDScript | C# | GDScript + C# | C# | C++ + Blueprint]
Knowledge Risk:  [LOW/MEDIUM/HIGH]
Reference Docs:  [created/skipped]
CLAUDE.md:       [updated]
Tech Prefs:      [created/updated]
project.yaml:    [created/updated]
Agent Config:    [verified]

Next Steps:
1. Review docs/engine-reference/<engine>/VERSION.md

Then print one Next-Steps list, matching the resolved workflow tier:

minimal — the lean 4-step floor (you are on step 1):

2. Run /brainstorm to produce your one-page design/game-brief.md (the lean-tier design artifact)
3. Run /create-stories to turn the brief's MVP list into stories
4. Run /dev-story — first line of game code

(No /map-systems, /design-system, /prototype, or /sprint-plan at minimal — the brief replaces the GDDs and its build order is the plan.)

standard / full — the full pipeline:

2. [If from /brainstorm] Run /map-systems to decompose your concept into individual systems
3. [If from /brainstorm] Run /design-system to author per-system GDDs (guided, section-by-section)
4. [If from /brainstorm] Run /prototype [core-mechanic] to validate the core idea before writing GDDs
5. [If fresh start] Run /brainstorm to discover your game concept
6. Create your first milestone: /sprint-plan new

Verdict: COMPLETE — engine configured and reference docs populated.

Guardrails

• NEVER guess an engine version — always verify via WebSearch or user confirmation
• project.yaml is the primary config store (v1.1). Always dual-write engine config to BOTH project.yaml (primary) and technical-preferences.md (legacy mirror). If the two ever diverge, project.yaml is authoritative.
• NEVER overwrite existing reference docs without asking — append or update
• If reference docs already exist for a different engine, ask before replacing
• Always show the user what you're about to change before making CLAUDE.md edits
• If WebSearch returns ambiguous results, show the user and let them decide
• When the user chose GDScript: copy the GDScript CLAUDE.md template from A1 in .claude/skills/setup-engine/references/godot-language-config.md exactly. NEVER add "C++ via GDExtension" to the Language field. GDScript projects may use GDExtension, but it is not a primary project language. The godot-gdextension-specialist in the routing table is available for when native extensions are needed — it does not make C++ a project language.

Appendix A — Godot Language Configuration

Moved out of this file so it costs nothing on non-Godot runs.

When the chosen engine is Godot, read .claude/skills/setup-engine/references/godot-language-config.md and use the subsection for the chosen language:

• A1 — CLAUDE.md Technology Stack templates (GDScript / C# / Both)
• A2 — naming conventions
• A3 — engine specialist routing and file-extension tables

Load discipline. On any engine other than Godot, never load it — nothing in Sections 4, 5 or 5.5 needs it, and reading it anyway spends the tokens the split exists to save. On Godot, read it once when you first reach Section 4 and keep using it for Sections 5 and 5.5; do not re-read it at each reference.