Domain language

Agent run envelope: the versioned, JSON-safe request contract created after ingress authentication and protocol validation but before agent, provider, tool, or MCP initialization. It carries only the validated protocol payload and the minimum trusted principal identifiers. The execution host rehydrates all runtime state from those identifiers.
Subagent thread: a durable, view-only child conversation owned by one parent conversation and subagent identity. A parent agent may continue it by stable threadId; each continuation uses a fresh execution lease restored from the canonical child transcript. It is not an ordinary human-writable chat.
Theme definition: a versioned, data-only description of LibreChat semantic colors and shared appearance roles, optionally specialized by light or dark mode. The theme module validates and resolves partial definitions against bundled defaults before adapters apply them. A theme definition does not contain arbitrary CSS, application behavior, or alternate feature layouts.