The same concepts appear throughout Kestrel even though each product provides a different experience. Learn them here when a guide uses an unfamiliar term.
Runtime
The runtime executes and records agent work. It advances runs through model and tool steps, persists events and results, and supports waiting, cancellation, recovery, and replay.
Execution Protocol
The Execution Protocol is the shared contract for commands, events, streams, and terminal results. Local Core and remote runner services expose the same protocol through different transports.
Local Core
Local Core is the runtime host on a user's computer. Desktop and local CLI/TUI workflows connect to it through an authenticated Unix socket. A local SDK target can use the same connection.
Runner service
A runner service is a network-hosted runtime endpoint for trusted application servers. Kestrel One and remote SDK targets use this form. Browser code should call its application server rather than hold runner credentials directly.
The kestrel web command is a local HTTP bridge to Local Core. It gives a local
server application a runner-service-compatible URL without starting another
runtime.
Run and terminal outcome
A run is one execution attempt. It ends as completed, failed, cancelled, or
waiting for a person or external condition. The terminal result keeps
human-facing assistantText separate from structured application data.
Agent
An agent is the application-facing definition created with createAgent().
It binds an identity and profile to an explicit local or remote execution target
and provides methods such as run, stream, resume, session, and
subscribe.
Session
A session is a durable line of continuity. It connects related turns, memory, events, and evidence so later work can continue instead of starting from an empty request.
Thread and Project
A Thread is the product-facing conversation and work history. In Kestrel One, a Project groups related Threads with members, instructions, files, and Knowledge. Desktop uses a local workspace rather than a hosted Project.
Workspace
A workspace is a local project folder known to Desktop or the CLI. It tells Kestrel where the work belongs; it does not automatically enable recurring automation.
Stream, subscription, and replay
A stream shows live events for the request that just started. A subscription follows selected persisted events. Replay uses recorded evidence to inspect work after it ends. They solve different jobs and are not one global event feed.
Operator control
Operator control lets a person inspect and act on work that already exists. Steering, stopping, resuming, and retrying remain attached to the original session instead of creating an unrelated conversation.