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Fleet Prime Agent is a stack of layered packages. Each layer has one job and talks to the next through a narrow interface.

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The layers

  • packages/agent — the agent runtime. Defines the event stream (AgentEvent), tool interface (AgentTool), and protocol contract.
  • packages/ai — the AI layer. Wraps every provider (OpenAI, Anthropic, Bedrock, Gemini, and 15 more) behind a single interface, plus a generated model registry with cost, context window, reasoning support, and thinking levels.
  • packages/coding-agent — the coding-agent runtime. Sessions, tools (ipython, shell, edit, grep, find), skills, extensions, refinement, compaction, subagents (rlm), CLI, and the daemon protocol all live here.
  • packages/tui — the interactive terminal client.
  • web/ — the Qredence UI, its server adapter, its design system, and its wire protocol.

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Key contracts

Everything crosses layers through a small number of typed contracts:
  • AgentSessionEvent — what a session emits: message_start, message_update, message_end, tool_execution_start, tool_execution_update, tool_execution_end.
  • ChatStreamEvent — the NDJSON events the web adapter emits to browsers: start, delta, tool, thinking, plan, state, queue, compaction, retry, done, error.
  • AgentMessage — the message payload written to session transcripts.
  • AgentTool — the interface every tool implements (execute, prepareArguments, beforeToolCall, afterToolCall).
  • Daemon protocol — DAEMON_PROTOCOL_VERSION plus DAEMON_SCHEMA_REVISION gate wire changes; new commands must be negotiated as capabilities before use.
See Streaming protocol for the wire format and Daemon protocol for versioning rules.

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Web app boundary

Only the web server adapter (web/server/src/event-mapper.ts) is allowed to import @earendil-works/* agent packages. Browser code never imports agent code directly; it consumes ChatStreamEvent over NDJSON and AgentSessionEvent over SSE, and renders every tool call as a card using the BEUI components in web/design.

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What runs where

  • Same process as the CLI: by default the agent runtime runs in the same Node process as the CLI. Good for scripts and one-shot runs.
  • Daemon: for long-lived work, run the agent as a daemon. CLI, TUI, and web all attach through DaemonClient and share sessions. See Daemon.
  • IPython kernel: every session gets its own persistent Python kernel provisioned lazily by prime-agent-runtime. That kernel is what makes state (variables, open files, network connections) survive across tool calls.
  • Subagents: rlm(...) calls inside a kernel spawn real child agent processes managed by SubagentRuntimeHost. See Subagents (RLM).
Last modified on August 17, 2026