Tianyi Cui
22e9152d8b
After turn/start was appended, nothing guaranteed a matching turn/end: a throw from a boundary emit (agent/turn-start, agent/step-start, the normal-path agent/turn-end) escaped runTurn, and the outer runLoop backstop logged an error but never appended turn/end — leaving an unbalanced turn that replay, telemetry, and the invariants plugin all assume is impossible. runTurn is restructured around idempotent finalizers that satisfy the four traps a naive finally would hit: - closeStep()/closeTurn(emit) are guarded (stepOpen/turnEnded) so they run at most once; the agent/step-end and agent/error emits are contained so a throwing listener can't strand the turn open. - failTurn() records the single error event + reason and emits agent/error exactly once (errorReported guard) — no double-logging when the outer catch also runs (e.g. a step error followed by a throwing turn-end listener). - the catch closes an open step BEFORE turn/end (invariants reject turn/end while a step is open), and rethrows ONLY pre-turn throws (turnStarted false), where no turn/end is owed, so the backstop still nets them. - disposal precedence: reason stays disposed only when disposed AND no error was reported; otherwise the error reason wins. Tests (with the invariants plugin loaded as a balance oracle): throwing turn-start (one error, one turn/end, no step), throwing step-start (step/end before turn/end), throwing agent/error on a step-error path (balanced, loop survives), disposal mid-turn (reason disposed, no error event), a pre-turn turn/start-append throw (rethrown to the backstop, no turn/end owed), and a step error + throwing turn-end listener (error logged exactly once). Verified all six fail against a simulated finalizer bypass. dsh-invariants added as an agent-loop devDependency (test-only oracle; no package cycle).
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