phase: Skill for Claude Code

add-engine-variant — Engine Enum Extension Gate

When to invoke

This skill is the gate for any work that would add a variant to an existing engine enum. Run it BEFORE:

• Proposing an engine extension in a plan or task description
• Drafting an engine PR that adds a variant
• Approving an audit verdict of "engine extension required"
• Wiring a converter arm to a not-yet-existing variant

If you find yourself about to type pub enum Foo { ... NewVariant ... } in crates/engine/src/, pause and run this skill.

The three filter stages — all must pass

Stage 1: Existence verification (5-grep protocol)

The variant might already exist under a different engine-native name. External data formats and the engine vocabulary are not 1:1; the engine often has the concept under a different name.

The canonical engine surface is data/engine-inventory.json (gitignored). Run cargo engine-inventory to (re)generate it locally before grepping for existing variants.

Run all five searches before considering extension:

# 1. Direct name search
rg -n "<concept_keyword>" crates/engine/src/types/

# 2. Inverse concept (engine often expresses "not X" as "X { negated: bool }" or "X { negated: true }")
rg -n "<inverse_concept>" crates/engine/src/types/

# 3. Inversion-parameter variants
rg -n "negated: bool|invert|polar" crates/engine/src/types/ability.rs

# 4. Native parser reverse dictionary — how does oracle_nom express this concept?
rg -n "<concept_keyword>|<engine_concept>" crates/engine/src/parser/oracle_*.rs

# 5. Synthesis layer
rg -n "<concept_keyword>" crates/engine/src/database/synthesis.rs

Stage 1 verdicts:

• EXISTS_SAME_NAME: variant exists. Stop. Wire to it.
• EXISTS_DIFFERENT_NAME: concept exists under an engine-native name (e.g., an external CreateTriggerUntil maps to engine Effect::CreateDelayedTrigger). Stop. Map the source data to the existing slot.
• EXISTS_AS_PARAMETER: concept exists as a parameter value of a more general variant (e.g., "untapped" exists as Tap { negated: true }). Stop. Use the parameter form.
• DOES_NOT_EXIST: proceed to Stage 2.