Function effectiveKeywords

Keyword resolution — unions an action's native keywords with any passive appendKeywords entries on the acting actor's active effects.

An append rule is { append, requiresKeyword }:

• requiresKeyword empty → unconditional; always contributes append
• requiresKeyword set → only contributes when the action's NATIVE keyword list contains that string

The filter checks native keywords only (not the merged list), so a rule with requiresKeyword: "X" can never trigger another rule that appends "X" — no cascades. Suppressed / disabled effects are skipped.