# description
A single atom in the prompt-atoms catalog. Discriminated by the top-level `type` field; one of: persona, constraint, format-instruction, tool-use-template, refusal-pattern, output-schema.

# properties.id.description
URL-safe slug; unique within the atom's type.

# properties.vendors.description
LLM families this atom is known to work well with. 'any' means vendor-agnostic.

# properties.content.description
The prompt fragment itself. For atoms with structured content (output-schema, tool-use-template), use the schema or template form; the renderer assembles it into a prompt turn. Empty string ('') is valid for stub/none atoms.

# properties.applicable_turns.description
Which turns this atom legally appears in. Defaults to ['system'] for persona/constraint/format-instruction/refusal-pattern; ['tool'] for tool-use-template; ['system','assistant'] for output-schema.

# properties.see_also.description
Sibling atoms commonly composed with this one.

# properties.persona_ref.description
Reference to a base persona atom. Format: <catalog>/persona/<slug>.