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name: custom-environments description: "Create and review PettingZoo AEC and Parallel custom environments, including factories, spaces, masks, wrappers, and versioned exports." disable-model-invocation: true metadata: disco-role: operating license: NOASSERTION

Custom Environments

Use this sub-skill when implementing or reviewing a new PettingZoo environment: AEC, Parallel, action-masked, versioned module exports, raw_env()/env() factories, or AgentSelector turn logic.

Start Here

• Read AEC authoring when the environment steps one agent at a time or needs direct AECEnv control.
• Read Parallel authoring when all live agents act in the same step or when exposing both parallel_env() and an AEC-compatible env().
• Read Action masking when observations or infos need valid-action masks or invalid-action policy.
• Read Troubleshooting when compliance tests fail around space identity, live-agent keys, dead agents, masks, seeding, render metadata, or wrapper ordering.
• Run custom_env_template.py for a bounded, dependency-light template that exposes parallel_env(), raw_env(), and wrapped env() factories.

Routing

• For compliance commands such as api_test, parallel_api_test, seed tests, render tests, or CI guidance, use the sibling testing-and-validation sub-skill.
• For conversion wrappers, utility wrapper behavior, and wrapper composition details, use the sibling wrappers-and-utilities sub-skill.
• For selecting and installing built-in PettingZoo environment families, use the sibling environment-families sub-skill.
• For ordinary rollout loops against an existing environment, use the sibling use-environments sub-skill.

Authoring Defaults

• Prefer Parallel authoring when agents truly act simultaneously; expose an AEC interface with parallel_to_aec when needed.
• Prefer direct AEC authoring when turns, delayed rewards, dead-agent stepping, or per-agent observations are easier to express one agent at a time.
• Keep possible_agents, spaces, and metadata stable after initialization; update agents only for the current episode lifecycle.
• Keep bundled examples and validation defaults bounded; large-cycle stress tests belong in explicit validation work, not default templates.