# 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.
- **MCP runtime request body**: trusted chat identifiers supplied only while an MCP server handles an agent request. It enables request-scoped header placeholders without retaining user-specific request data on a shared server definition.
- **Caller Capability Projection**: the versioned, SDK-owned classification of currently active tools by direct and programmatic callers. Event-driven execution transports this projection as data; LibreChat intersects it with its trusted registry and never recomputes deferred-tool discovery policy or treats the projection as authorization.
- **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.
- **Live subagent task owner**: the one API process holding a detached child execution, its abort controller, and its bounded control queue. Redis may route trusted poll/control envelopes to that owner, but it does not migrate or persist the executor; Mongo persists only the logical child thread and its continuation fence.
- **Subagent completion wakeup**: a durable internal `continue` trigger pre-registered before detached child execution so a process crash cannot lose the wakeup. Delivery defers until the child's terminal transcript is persisted, targets the initiating agent and exact parent response branch, carries task metadata rather than child output, waits for the parent generation to settle, and starts the parent turn that collects the result through the existing task store.
- **Subagent activity stream**: an observational, task-scoped live projection of bounded child progress for the currently open private panel. It may cross API replicas through Redis, never carries hidden reasoning text, and never controls or settles execution. The durable child thread remains canonical and its existing polling view is the fallback for missed or unavailable live events.
- **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.