refactor(events): document event-domain semantics, drop step-boundary mirror emits
Pin the three-domain rule (session = durable fact log, agent = live runtime surface, tools = registry/exec): a durable replayable fact is a SessionEvent; a live interception or transient/live-object signal is an agent/tools Cordis event. A boundary that is both is mirrored as an agent/* emit ONLY where a live consumer needs the Agent handle. Apply it to the boundary twins: drop agent/step-start and agent/step-end (no production consumer needs the live Agent at a step boundary — consumers read the durable step/start/step/end session events). Keep agent/turn-start/turn-end (the stdio UI labels output by agent.id). Tests that observed step boundaries via the removed emits now observe the durable session events; the pinned behavior is unchanged. Conservative subset of the proposed "remove boundary mirror events" simplification; foundation for the Hooks subsystem's canonical event surface.
This commit is contained in:
Tianyi Cui
@@ -147,7 +147,7 @@ export interface LoopHandle {
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* drain queued → 'turn/start' → session('user/message'…) → emit agent/turn-start
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* STEP loop:
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* drain steering → session('steering/message') ⟵ catches late steering
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* session('step/start'); emit agent/step-start ⟵ append before emit (the event-sourcing RFC)
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* session('step/start') ⟵ durable step boundary (no agent/* mirror)
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* assembly = ctx.systemPrompt.assemble() ⟵ waterfall system-prompt/assemble
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* req = {model, system, tools, messages: session.deriveMessages(), signal}
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* req = waterfall agent/request ⟵ hooks/compaction/model-switch
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@@ -159,7 +159,7 @@ export interface LoopHandle {
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* session('tool/call'); ctx.tools.execute() ⟵ waterfall tools/execute
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* session('tool/result')
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* drain steering → session('steering/message'); emit agent/steering
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* emit agent/step-end
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* session('step/end') ⟵ durable step boundary (no agent/* mirror)
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* cont = waterfall agent/turn-continuation(default = hadToolCalls || steered)
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* if !cont && steering arrived from step-end/continuation listeners: cont = true
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* if !cont: break
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@@ -279,33 +279,29 @@ async function runTurn(ctx: Context, agent: ReactLoopAgent, handle: LoopHandle,
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let stepOpen = false
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let errorReported = false
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// Close the open step exactly once (idempotent via stepOpen). The
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// agent/step-end emit is contained: a throwing step-end listener must not
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// abort finalization and strand the turn open (turn/end balance > notifying
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// one bad listener). Appended before the emit (the event-sourcing RFC append-before-emit).
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// Close the open step exactly once (idempotent via stepOpen). Step boundaries
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// are durable session events only — there is no agent/* step emit to mirror
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// them (see the agent event-domain rule). A throwing step/end session-event
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// listener must not abort finalization and strand the turn open (turn/end
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// balance > notifying one bad listener); it is contained and surfaced as a
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// turn error below.
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const closeStep = (): boolean => {
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if (!stepOpen) return false
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stepOpen = false
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// Session.append pushes step/end BEFORE notifying session/event listeners,
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// so a throwing listener leaves step/end in the log (balance holds) but
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// would otherwise abort finalization. Contain it and surface it as a turn
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// error below — the same outcome as a throwing agent/step-end listener.
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// error below.
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let failure: unknown
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try {
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session.append('step/end', { turn, step })
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} catch (error: unknown) {
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failure = error
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}
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try {
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ctx.emit('agent/step-end', agent, turn, step)
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} catch (error: unknown) {
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failure ??= error
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}
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// A throwing step/end session-event listener OR a throwing agent/step-end
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// listener surfaces as a turn error via failTurn (idempotent). This prevents
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// a throwing listener from producing a silent "completed" turn when the step
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// itself succeeded, AND keeps finalization going when closeStep runs from
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// the outer catch.
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// A throwing step/end session-event listener surfaces as a turn error via
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// failTurn (idempotent). This prevents a throwing listener from producing a
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// silent "completed" turn when the step itself succeeded, AND keeps
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// finalization going when closeStep runs from the outer catch.
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if (failure !== undefined) {
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failTurn(toError(failure))
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return true
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@@ -382,24 +378,23 @@ async function runTurn(ctx: Context, agent: ReactLoopAgent, handle: LoopHandle,
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while (true) {
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step += 1
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// Steering from the previous round's step-end/continuation listeners
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// (or turn-start listeners on the first step) joins before the request.
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// Steering from the previous round's continuation listeners (or
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// turn-start listeners on the first step) joins before the request.
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drainSteering(ctx, agent, turn)
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session.append('step/start', { turn, step })
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stepOpen = true
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ctx.emit('agent/step-start', agent, turn, step)
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const abort = new AbortController()
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handle.setAbort(abort)
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// Cancel landing in the step-start window: a synchronous `agent/turn-start`
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// or `agent/step-start` listener (both fire before this point) can have
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// called `cancel()`, and `runStep` would otherwise run a full extra step
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// with no AbortController having observed it. Check the marker AFTER
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// setAbort (so the next-iteration drain sees a clean controller) and before
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// `runStep`: drop the step, end the turn `aborted`. closeStep balances the
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// already-appended step/start.
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// listener (fires before this point) can have called `cancel()`, and
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// `runStep` would otherwise run a full extra step with no AbortController
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// having observed it. Check the marker AFTER setAbort (so the
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// next-iteration drain sees a clean controller) and before `runStep`: drop
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// the step, end the turn `aborted`. closeStep balances the already-appended
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// step/start.
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if (handle.isCancelled()) {
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handle.setAbort(undefined)
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reason = { kind: 'aborted', reason: handle.cancelReason() }
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@@ -204,7 +204,7 @@ describe('Agent.cancel()', () => {
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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let steps = 0
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ctx.on('agent/step-start', () => { steps += 1 })
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ctx.on('session/event', (_session, event) => { if (event.type === 'step/start') steps += 1 })
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const reasons: TurnEndReason[] = []
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ctx.on('agent/turn-end', (_a, _t, reason) => void reasons.push(reason))
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@@ -46,15 +46,21 @@ describe('agent loop', () => {
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const ctx = await harness(adapter)
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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// Turn boundaries are live agent/* emits; step boundaries are durable
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// session events only (no agent/* mirror). Interleave both feeds in fire
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// order to assert the full boundary nesting.
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const order: string[] = []
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for (const name of ['agent/turn-start', 'agent/step-start', 'agent/step-end', 'agent/turn-end'] as const) {
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for (const name of ['agent/turn-start', 'agent/turn-end'] as const) {
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ctx.on(name, () => void order.push(name))
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}
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ctx.on('session/event', (_session, event) => {
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if (event.type === 'step/start' || event.type === 'step/end') order.push(event.type)
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})
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send(agent, 'hi')
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await waitForIdle(ctx, agent)
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expect(order).toEqual(['agent/turn-start', 'agent/step-start', 'agent/step-end', 'agent/turn-end'])
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expect(order).toEqual(['agent/turn-start', 'step/start', 'step/end', 'agent/turn-end'])
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const types = agent.session.events.map(e => e.type)
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// turn/start opens the turn, THEN the queued user message is recorded inside
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@@ -269,7 +275,7 @@ describe('agent loop', () => {
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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let steps = 0
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ctx.on('agent/step-end', () => void steps++)
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ctx.on('session/event', (_session, event) => { if (event.type === 'step/end') steps++ })
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ctx.on('agent/turn-continuation', async (_agent, _turn, _defaultDecision, next) => {
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if (steps < 3) return true
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return next()
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@@ -371,7 +377,7 @@ describe('agent loop', () => {
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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let steps = 0
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ctx.on('agent/step-end', () => void steps++)
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ctx.on('session/event', (_session, event) => { if (event.type === 'step/end') steps++ })
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// Force exactly one continuation (step 1 → step 2), then defer to default
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// (step 2 is a plain stop with no tool calls → stops).
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ctx.on('agent/turn-continuation', async (_agent, _turn, _defaultDecision, next) => {
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@@ -536,7 +542,7 @@ describe('agent loop', () => {
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])
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})
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it('stops the turn when agent/step-end listener failure has recorded an error', async () => {
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it('stops the turn when a step/end session-event listener failure has recorded an error', async () => {
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const adapter = new MockAdapter([
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toolCallResponse('c1', 'echo', { text: 'x' }),
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textResponse('should not run'),
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@@ -552,8 +558,11 @@ describe('agent loop', () => {
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}))
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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let threw = false
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ctx.on('agent/step-end', () => {
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if (!threw) { threw = true; throw new Error('bad step-end listener') }
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// A throwing step/end session-event listener is the surviving boundary-listener
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// failure path (step boundaries have no agent/* mirror): closeStep contains it
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// and surfaces it as a turn error rather than stranding the turn open.
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ctx.on('session/event', (_session, event) => {
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if (event.type === 'step/end' && !threw) { threw = true; throw new Error('bad step/end listener') }
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})
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send(agent, 'go')
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@@ -144,36 +144,6 @@ describe('HIGH: abort during tool execution ends the turn', () => {
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})
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describe('HIGH: steering from late extension points is never stranded', () => {
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it('steer() from an agent/step-end listener reaches the next request (/goal pattern)', async () => {
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const adapter = new MockAdapter([
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toolCallResponse('c1', 'echo', { text: 'x' }),
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textResponse('after steering'),
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])
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const ctx = await harness(adapter)
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ctx.tools.register(defineTool({
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name: 'echo',
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description: '',
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parameters: { text: { type: 'string' } },
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async execute(args) {
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return [{ type: 'text', text: String(args.text) }]
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},
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}))
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const agent = ctx.agentLoop.create(AgentId('a1'), { model: 'mock' })
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let steeredOnce = false
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ctx.on('agent/step-end', () => {
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if (steeredOnce) return
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steeredOnce = true
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agent.steer([{ type: 'text', text: 'goal reminder from step-end' }])
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})
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send(agent, 'go')
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await waitForIdle(ctx, agent)
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expect(adapter.requests).toHaveLength(2)
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expect(JSON.stringify(adapter.requests[1]!.messages)).toContain('goal reminder from step-end')
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})
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it('steer() from an agent/turn-continuation listener overrides a stop decision', async () => {
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const adapter = new MockAdapter([
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textResponse('no tools, would stop here'),
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@@ -539,24 +509,26 @@ describe('HIGH: a finish-error stream chunk ends the turn as error, not complete
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})
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})
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describe('P1-6: step/start is appended before agent/step-start is emitted', () => {
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it('a step-start listener sees the step/start event already in session.events', async () => {
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describe('P1-6: a step/start session-event listener sees the event already in the log', () => {
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it('the step/start event is in session.events when its session/event listener fires', async () => {
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const adapter = new MockAdapter([textResponse('done')])
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const ctx = await harness(adapter)
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const agent = ctx.agentLoop.create(AgentId('a-step-order'), { model: 'mock' })
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// Capture, at the moment agent/step-start fires, whether the matching
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// step/start event is already in the log (append-before-emit, the event-sourcing RFC).
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// Session.append pushes the event BEFORE notifying session/event listeners,
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// so a step/start listener always finds the matching event already in the
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// log. (Step boundaries have no agent/* mirror — the session log is the live
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// feed.)
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const observed: { turn: number; step: number; lastEventType: string | undefined; sawStepStart: boolean }[] = []
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ctx.on('agent/step-start', (subject, turn, step) => {
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if (subject !== agent) return
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const events = [...subject.session.events]
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ctx.on('session/event', (subject, event) => {
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if (subject !== agent.session || event.type !== 'step/start') return
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const events = [...subject.events]
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const last = events.at(-1)
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observed.push({
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turn,
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step,
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turn: event.data.turn,
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step: event.data.step,
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lastEventType: last?.type,
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sawStepStart: events.some(e => e.type === 'step/start' && e.data.turn === turn && e.data.step === step),
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sawStepStart: events.some(e => e.type === 'step/start' && e.data.turn === event.data.turn && e.data.step === event.data.step),
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})
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})
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@@ -621,29 +593,35 @@ describe('P1-5: a started turn (and any open step) is always closed on a boundar
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expect(adapter.requests).toHaveLength(0)
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})
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it('a throwing agent/step-start listener closes the open step then the turn (step/end before turn/end)', async () => {
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it('a throwing step/start session-event listener fails the turn balanced (no step stranded open)', async () => {
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const adapter = new MockAdapter([textResponse('never reached')])
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const ctx = await balancedHarness(adapter)
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const agent = ctx.agentLoop.create(AgentId('a-stepstart'), { model: 'mock' })
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// Step boundaries have no agent/* mirror; a throwing step/start session-event
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// listener is the surviving step-boundary-listener failure. The throw fires
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// INSIDE session.append('step/start') — before the loop marks the step open —
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// so the loop never had an open step to close (no step/end is owed). The
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// throw drives the outer catch, which fails the turn balanced. The invariants
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// oracle (balancedHarness) rejects any imbalance, so a green run proves the
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// turn/start..turn/end nesting holds with a lone step/start and no step/end.
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let threw = false
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ctx.on('agent/step-start', () => { if (!threw) { threw = true; throw new Error('boom step-start') } })
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ctx.on('session/event', (_s, event) => {
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if (event.type === 'step/start' && !threw) { threw = true; throw new Error('boom step-start') }
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})
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const errors: Error[] = []
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ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
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send(agent, 'go')
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await waitForIdle(ctx, agent)
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const e = [...agent.session.events]
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const c = boundaryCounts(agent)
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expect(c).toMatchObject({ turnStart: 1, turnEnd: 1, stepStart: 1, stepEnd: 1, errors: 1 })
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// step/start was appended (Session.append pushes before notifying), but the
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// listener throw pre-empted the loop marking the step open, so no step/end is
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// owed; the turn still closes exactly once with an error, balanced.
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expect(c).toMatchObject({ turnStart: 1, turnEnd: 1, stepStart: 1, stepEnd: 0, errors: 1 })
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expect(errors.map(x => x.message)).toEqual(['boom step-start'])
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// step/end must precede turn/end (the invariants oracle would reject
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// turn/end-while-step-open, but assert the order explicitly too).
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const stepEndIdx = e.findIndex(x => x.type === 'step/end')
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const turnEndIdx = e.findIndex(x => x.type === 'turn/end')
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expect(stepEndIdx).toBeGreaterThanOrEqual(0)
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expect(stepEndIdx).toBeLessThan(turnEndIdx)
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expect(c.lastTurnEnd?.type === 'turn/end' && c.lastTurnEnd.data.reason.kind).toBe('error')
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})
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it('a throwing agent/error listener during a step-error path still balances the turn, loop survives', async () => {
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@@ -829,17 +807,20 @@ describe('P1-5: a started turn (and any open step) is always closed on a boundar
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expect(boundaryCounts(agent).turnEnd).toBe(2)
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})
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it('a throwing agent/step-end listener during a successful step ends the turn as error, not completed', async () => {
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// closeStep() must surface a throwing step-end listener via failTurn so the
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it('a throwing step/end session-event listener during a successful step ends the turn as error, not completed', async () => {
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// closeStep() must surface a throwing step/end listener via failTurn so the
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// turn ends with reason error, not a silent "completed" with the throw
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// swallowed. Regression test for the closeStep() catch that previously
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// swallowed the throw in the normal (no-tool, no-steering) path.
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// swallowed the throw in the normal (no-tool, no-steering) path. (Step
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// boundaries have no agent/* mirror; the session-event listener is the path.)
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const adapter = new MockAdapter([textResponse('all good'), textResponse('turn 2 ok')])
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const ctx = await balancedHarness(adapter)
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const agent = ctx.agentLoop.create(AgentId('a-stepend-throw'), { model: 'mock' })
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let threw = false
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ctx.on('agent/step-end', () => { if (!threw) { threw = true; throw new Error('boom step-end') } })
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ctx.on('session/event', (_s, event) => {
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if (event.type === 'step/end' && !threw) { threw = true; throw new Error('boom step-end') }
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})
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const errors: Error[] = []
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ctx.on('agent/error', (_a, _t, _s, error) => void errors.push(error))
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@@ -903,18 +884,18 @@ describe('P1-5: a started turn (and any open step) is always closed on a boundar
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})
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it('a throwing session/event listener on step/end during finalization still appends turn/end', async () => {
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// A throwing agent/step-start listener drives the outer catch, which calls
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// closeStep() during finalization. closeStep appends step/end; a
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// A finish-error stream opens a step then fails it, driving finalization
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// through closeStep() with the step open. closeStep appends step/end; a
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// session/event listener throwing on THAT must not abort the catch before
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// closeTurn(false) — step/end is already logged (balance holds) and the
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// throw is contained + surfaced via failTurn, so turn/end is still appended.
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const adapter = new MockAdapter([textResponse('never reached')])
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// closeTurn — step/end is already logged (balance holds) and the throw is
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// contained + surfaced via failTurn, so turn/end is still appended. (The
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// failed step itself also routes through failTurn; the step/end-listener
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// throw is the second, contained, failure.)
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const errorStream: StreamChunk[] = [{ type: 'finish', reason: { kind: 'error', message: 'provider 500' } }]
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const adapter = new MockAdapter([errorStream, textResponse('turn 2 ok')])
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const ctx = await harness(adapter)
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const agent = ctx.agentLoop.create(AgentId('a-stependthrow'), { model: 'mock' })
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// Open a step, then make the agent/step-start emit throw (boundary throw →
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// outer catch → closeStep during finalization).
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ctx.on('agent/step-start', () => { throw new Error('boom step-start') })
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let threw = false
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ctx.on('session/event', (_s, event) => {
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if (!threw && event.type === 'step/end') { threw = true; throw new Error('boom step/end listener') }
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