Tianyi Cui
825b57aff9
Introduce HarnessError in dsh-llm (the leaf package): a stable machine-routable
code distinct from the message, cause chaining, name from the subclass, plus
isHarnessError. LlmError, ToolArgsError, and InvariantError now extend it.
Tool failures carry the structure end-to-end: ToolExecutionResult gains
error: { name, code } (populated from a thrown HarnessError), and the loop
forwards it onto the tool/result session event (which gained the same optional
field) for retry/sandbox plugins and replay. The loop's toError wraps non-Error
throws in a HarnessError(code: UNKNOWN, cause) instead of a bare Error.
Landed last and in isolation so it's a pure upgrade over the plain Error+code
the earlier PRs used — independently revertible. Graduates RFC 005 pt 2 ->
ADR 0015; RFC 005 now fully implemented.
dsh-agent-loop
THE concrete agent plugin: LoopAgent and the loop driver. Implements the Agent interface and drives the session/turn/step lifecycle.
This is the only package in the harness that contains concrete loop logic. Everything else is an abstract service or a plugin against extension seams — new behavior goes into plugins, not here.
Service: AgentLoop (ctx key: agentLoop)
Public API
ctx.agentLoop.create(id: string, options?: AgentOptions): LoopAgentCreate an agent, start its loop, and register it inctx.agents. Disposed with the calling fiber.
Injected services
agents, sessions, llm, tools, systemPrompt — all five interface services.
Configuration (schemastery)
interface Config {
agents: Array<{
id: string // required
model?: string
systemPrompt?: string
}>
}
Agents listed in config are auto-created at startup.
Classes
LoopAgent— the concreteAgentimplementation. Owns the inbox (Inbox), the per-stepAbortController, and the loop driver. Everything observable happens through session events and theagent/*event taxonomy.Inbox— per-agent queued + steering FIFOs (enqueue,steer,drainQueued,drainSteering,waitForQueued).
Loop lifecycle (loop.ts)
One invocation of runLoop() drives one agent for its whole lifetime:
forever:
wait for queued messages (idle)
TURN (error-contained):
drain queued → session('user/message') → 'turn/start'
STEP loop:
drain steering
assembly = systemPrompt.assemble()
request = waterfall agent/request
stream llm.stream(request) → session('assistant/chunk')
message = waterfall agent/step-result
session('assistant/message')
each tool-call: session('tool/call') → tools.execute() → session('tool/result')
drain steering → session('steering/message')
cont = waterfall agent/turn-continuation
if !cont: break
session('turn/end')
await session/flush
re-enqueue leftover steering as queued
idle unless more queued
Error containment: a throwing plugin ends the turn, never the loop. Dispose mid-turn emits agent/status('disposed') and ends with reason disposed.
What is NOT here
Everything that goes beyond "call the model, run the tools, repeat" belongs to plugins listening on the event taxonomy:
- Hooks:
agent/request,agent/step-result,tools/execute,agent/turn-continuation - Compaction:
agent/request - Sandbox, permission, plan mode:
tools/execute - Sub-agents: TODO seam on
AgentLoop.create() - Persistence:
session/event+session/flush - UI:
agent/stream-chunk+agent/*events