ADR-0001: Engine Specialist Separation Policy

[gentlius]

Codifies when an engine family adds a separate language-quality specialist agent vs absorbs language quality into the framework primary. Policy: separate only when multiple distinct languages co-exist within the same project; absorb when a single language is the de-facto framework requirement.

Retroactively explains the existing Godot (separate GDScript + C#) vs Unity (C# absorbed) vs Unreal (Blueprint separate, C++ absorbed) asymmetry, and provides a mechanical rule for future engine family additions.

Originating fork accepted this as policy when adding the HTML5 engine family (TypeScript absorbed into pixijs-specialist). Submitted upstream as Proposed for adoption — independent value even without the HTML5 family PR.

Summary

Adds the framework's first ADR — a written rule for when an engine family gets a separate language-quality specialist agent vs. absorbs language quality into the framework primary. Resolves the implicit asymmetry between existing engine sets (Godot has separate GDScript+C# specialists, Unity has none, Unreal has Blueprint-only).

Submitted as Proposed for upstream adoption (accepted in originating fork during the HTML5 engine family addition session).

Type of Change

• New agent
• New skill
• New hook or rule
• Bug fix
• Documentation improvement
• Other: First ADR for the framework itself (governs agent architecture decisions, not game runtime architecture)

Changes

• Adds docs/architecture/001-engine-specialist-separation-policy.md (161 lines)
• States the rule: separate specialist only when multiple distinct languages co-exist within the same project; absorb when a single language is the de-facto framework requirement
• Mechanically applies the rule to existing engines (Godot/Unity/Unreal) — retroactively justifies the current asymmetry
• Includes Alternatives Considered (Always Separate / Always Absorb / No Rule) with rationales for rejection
• Provides a "Definition of Structurally Different" subsection to handle edge cases (e.g., Lua + C++ scripting languages, future Bevy/Rust)

Checklist

• I've tested this in a Claude Code session — applied as policy in originating fork
• New agents include the Collaboration Protocol section — N/A (no new agents)
• New skills use the subdirectory format (.claude/skills/<name>/SKILL.md) — N/A (no new skills)
• Reference docs are updated (agent-roster, skills-reference, hooks-reference, rules-reference) — N/A (policy doc, not referenced by index files)
• Hooks use grep -E (POSIX) and fail gracefully without jq/python — N/A (no hooks)
• No hardcoded paths or platform-specific assumptions

Notes

This ADR pairs with a separate PR adding the HTML5/PixiJS engine family. The HTML5 PR's choice to absorb TypeScript into pixijs-specialist (rather than add a sixth agent) is justified by this rule. The two PRs can be reviewed independently — this ADR has standalone value as documentation of existing framework asymmetry.