deepseek-harness/packages/core/agent-loop/tests/cancel.spec.ts

/**
 * Tests for the queue-aware `Agent.cancel()` primitive. `cancel()` is the broad verb — it
 * clears queued + steering work, aborts the active turn, and drops work not yet claimed by the
 * driver without leaking cancellation into a replacement prompt. The suite covers every landing
 * window plus signal reset and `whenIdle()` quiescence.
 * @module dsh-agent-loop/tests/cancel
 */

import { describe, expect, it, vi } from 'vitest'
import { Context } from 'cordis'
import LlmService from '@deepseek-ai/dsh-llm'
import SessionStore, { SessionId, TurnEndReason } from '@deepseek-ai/dsh-session'
import SystemPrompt from '@deepseek-ai/dsh-system-prompt'
import ToolRegistry, { defineContentToolFixture, TOOL_ABORTED_BEFORE_DISPATCH } from '@deepseek-ai/dsh-tools'
import AgentRegistry, { type Agent } from '@deepseek-ai/dsh-agent'
import AgentLoop from '@deepseek-ai/dsh-agent-loop'
import { MockAdapter, textResponse, toolCallResponse } from './mock-adapter.ts'

function driverDone(agent: Agent): Promise<void> {
  return (agent as Agent & { done: Promise<void> }).done
}

async function harness(adapter: MockAdapter) {
  const ctx = new Context()
  await ctx.plugin(LlmService)
  await ctx.plugin(SessionStore)
  await ctx.plugin(SystemPrompt)
  await ctx.plugin(ToolRegistry)
  await ctx.plugin(AgentRegistry)
  await ctx.plugin(AgentLoop, { agents: [] })
  ctx.llm.registerAdapter(['mock'], adapter)
  return ctx
}

function send(agent: Agent, text: string) {
  agent.followup({ content: [{ type: 'text', text }], source: { kind: 'user' } })
}

/** Resolve on the agent's next idle transition (event-based, not status poll). */
function waitForIdle(ctx: Context, agent: Agent): Promise<void> {
  return new Promise((resolve) => {
    const dispose = ctx.on('agent/status', (subject, status) => {
      if (subject === agent && status === 'idle') { dispose(); resolve() }
    })
  })
}

/** All user-message texts recorded in the log (to assert what actually ran). */
function userTexts(agent: Agent): string[] {
  return agent.session.events
    .filter(e => e.type === 'user/message')
    .flatMap(e => e.type === 'user/message' ? e.data.content : [])
    .flatMap(b => b.type === 'text' ? [b.text] : [])
}

describe('Agent.cancel()', () => {
  it('notifies every observer before clearing work and contains listener failures', async () => {
    const adapter = new MockAdapter([textResponse('must remain unused')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('cancel-event'), { provider: 'mock', model: 'mock' })
    const warned = vi.spyOn(ctx.logger, 'warn').mockImplementation(() => {})
    const seen: string[] = []
    ctx.on('agent/cancel-requested', (subject, cause) => {
      if (subject !== agent) return
      seen.push(`first:${cause.kind}`)
      subject.followup({ content: [{ type: 'text', text: 'queued by cancel observer' }], source: { kind: 'user' } })
      throw new Error('observer failed')
    })
    ctx.on('agent/cancel-requested', (subject, cause) => {
      if (subject === agent) seen.push(`second:${cause.kind}`)
    })

    send(agent, 'drop me')
    agent.cancel({ kind: 'user' })
    await new Promise(resolve => setTimeout(resolve, 30))
    agent.cancel({ kind: 'parent' })

    expect(seen).toEqual(['first:user', 'second:user'])
    expect(userTexts(agent)).toEqual([])
    expect(adapter.requests).toHaveLength(0)
    expect(warned).toHaveBeenCalledWith(expect.stringContaining('agent/cancel-requested'))
  })

  it('cancel() on an idle agent with nothing queued is a no-op; the next prompt runs (F2 leak guard)', async () => {
    const adapter = new MockAdapter([textResponse('reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // The loop is parked at the idle wait with nothing queued. A cancel here must
    // NOT arm the marker — otherwise the next legitimate prompt would be dropped.
    agent.cancel({ kind: 'user' })

    send(agent, 'real prompt')
    await waitForIdle(ctx, agent)

    // The prompt ran: its user message is in the log and one turn completed.
    expect(userTexts(agent)).toEqual(['real prompt'])
    expect(agent.session.events.some(e => e.type === 'turn/end')).toBe(true)
  })

  it('cancel({ keepInbox: true }) preserves queued work and emits no discard', async () => {
    const adapter = new MockAdapter([textResponse('reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
    const discards: unknown[] = []
    ctx.on('agent/inbox/discard', (subject, items) => { if (subject === agent) discards.push(items) })
    const cancelRequests: unknown[] = []
    ctx.on('agent/cancel-requested', (subject, cause) => { if (subject === agent) cancelRequests.push(cause) })

    // Queue a turn WITHOUT waking the driver, so it sits in the inbox.
    agent.send({ content: [{ type: 'text', text: 'preserved' }], source: { kind: 'user' } }, { target: 'next-turn', wakeup: false })
    // keepInbox cancel: no active turn, work preserved, no discard event. With
    // nothing to abort and nothing discarded, the call is a documented no-op,
    // so it emits no cancel-requested either.
    agent.cancel({ kind: 'user' }, { keepInbox: true })
    expect(discards).toEqual([])
    expect(cancelRequests).toEqual([])

    // The preserved item still runs once the driver is woken by a later send.
    send(agent, 'wake it')
    await waitForIdle(ctx, agent)
    expect(userTexts(agent)).toEqual(['preserved', 'wake it'])
  })

  it('a lone quiet (wakeup:false) send leaves the agent parked at idle', async () => {
    const adapter = new MockAdapter([textResponse('reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // A quiet item alone must NOT wake the driver: no turn runs and whenIdle
    // resolves (the agent is quiescent), leaving the item queued.
    agent.send({ content: [{ type: 'text', text: 'quiet' }], source: { kind: 'user' } }, { target: 'next-turn', wakeup: false })
    await agent.whenIdle()
    expect(agent.status).toBe('idle')
    expect(agent.session.events.some(e => e.type === 'turn/start')).toBe(false)

    // A later waking send drives the loop, and the quiet item rides along first.
    send(agent, 'wake')
    await waitForIdle(ctx, agent)
    expect(userTexts(agent)).toEqual(['quiet', 'wake'])
  })

  it('cancelling a parked quiet item settles a pending whenIdle() without a later send', async () => {
    const adapter = new MockAdapter([textResponse('reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    agent.send({ content: [{ type: 'text', text: 'quiet' }], source: { kind: 'user' } }, { target: 'next-turn', wakeup: false })
    const idle = agent.whenIdle()
    agent.cancel({ kind: 'user' })
    await idle
    expect(agent.session.events.some(e => e.type === 'turn/start')).toBe(false)
  })

  it('pre-step cancel drops the about-to-start turn (no turn is opened)', async () => {
    const adapter = new MockAdapter([textResponse('should not run')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // send() queues synchronously (status still idle, loop microtask not yet
    // resumed). Cancel in that pre-step window: the queued turn must not run.
    send(agent, 'drop me first')
    send(agent, 'drop me second')
    agent.cancel({ kind: 'user' })

    // Give the loop a chance to wake and process the cancel.
    await new Promise(r => setTimeout(r, 30))

    // No turn was opened — the queued prompt was dropped, never recorded.
    expect(userTexts(agent)).toEqual([])
    expect(agent.session.events.some(e => e.type === 'turn/start')).toBe(false)
    expect(agent.status).toBe('idle')
  })

  it('disposal from the running notification drops queued work before turn start', async () => {
    const adapter = new MockAdapter([textResponse('should not run')])
    const ctx = await harness(adapter)
    const handle = await ctx.agents.create({
      sessionId: SessionId('dispose-running-session'),
      agentOptions: { provider: 'mock', model: 'mock' },
    })
    const agent = handle.agent

    const running = Promise.withResolvers<undefined>()
    let disposalDone: Promise<void> | undefined
    ctx.on('agent/status', (subject, status) => {
      if (subject !== agent || status !== 'running') return
      disposalDone = handle.dispose()
      running.resolve(undefined)
    })

    send(agent, 'drop before claim')
    await running.promise
    if (disposalDone === undefined) throw new Error('running listener did not start disposal')
    await disposalDone
    await driverDone(agent)

    expect(agent.status).toBe('idle')
    expect(agent.session.events.some(event => event.type === 'turn/start')).toBe(false)
    expect(userTexts(agent)).toEqual([])
    expect(adapter.requests).toHaveLength(0)
  })

  it('a whenIdle() waiter registered BEFORE a pre-step cancel resolves (F1 hang guard)', async () => {
    const adapter = new MockAdapter([textResponse('x')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // This waiter cannot rely on a running→idle transition because cancellation
    // drops the turn before it runs; the skip path must settle it directly.
    send(agent, 'q')
    const idle = agent.whenIdle()
    agent.cancel({ kind: 'user' })

    // Must resolve (not hang). A timeout makes the failure a clear test failure.
    await Promise.race([
      idle,
      new Promise((_r, reject) => setTimeout(() => { reject(new Error('whenIdle hung after pre-step cancel')) }, 1000)),
    ])
    expect(agent.status).toBe('idle')
  })

  it('idle-listener cancellation settles its waiter without cancelling later work', async () => {
    const adapter = new MockAdapter([textResponse('first reply'), textResponse('later reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('idle-listener-cancel'), { provider: 'mock', model: 'mock' })

    const replacementRegistered = Promise.withResolvers<undefined>()
    let replacementObservation: Promise<{ status: string; requests: number; turns: number }> | undefined
    ctx.on('agent/status', (subject, status) => {
      if (subject !== agent || status !== 'idle' || replacementObservation !== undefined) return
      send(agent, 'cancelled replacement')
      replacementObservation = agent.whenIdle().then(() => ({
        status: agent.status,
        requests: adapter.requests.length,
        turns: agent.session.events.filter(event => event.type === 'turn/start').length,
      }))
      agent.cancel({ kind: 'user' })
      replacementRegistered.resolve(undefined)
    })

    send(agent, 'first')
    await replacementRegistered.promise
    if (replacementObservation === undefined) throw new Error('idle listener did not register replacement work')

    await expect(Promise.race([
      replacementObservation,
      new Promise((_resolve, reject) => setTimeout(() => { reject(new Error('whenIdle hung after idle-listener cancel')) }, 1000)),
    ])).resolves.toEqual({ status: 'idle', requests: 1, turns: 1 })

    const idle = waitForIdle(ctx, agent)
    send(agent, 'later')
    await idle
    expect(adapter.requests).toHaveLength(2)
    expect(userTexts(agent)).toEqual(['first', 'later'])
  })

  it('replacement work queued after idle-listener cancellation still runs', async () => {
    const adapter = new MockAdapter([textResponse('first reply'), textResponse('replacement reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('idle-listener-post-cancel-send'), { provider: 'mock', model: 'mock' })

    const replacementRegistered = Promise.withResolvers<undefined>()
    let replacementIdle: Promise<void> | undefined
    ctx.on('agent/status', (subject, status) => {
      if (subject !== agent || status !== 'idle' || replacementIdle !== undefined) return
      send(agent, 'cancelled replacement')
      agent.cancel({ kind: 'user' })
      send(agent, 'surviving replacement')
      replacementIdle = agent.whenIdle()
      replacementRegistered.resolve(undefined)
    })

    send(agent, 'first')
    await replacementRegistered.promise
    if (replacementIdle === undefined) throw new Error('idle listener did not register replacement work')
    await replacementIdle

    expect(adapter.requests).toHaveLength(2)
    expect(userTexts(agent)).toEqual(['first', 'surviving replacement'])
  })

  it('cancel() mid-step aborts the active turn and drops every queued tail item', async () => {
    const adapter = new MockAdapter(['hang'])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    const reasons: TurnEndReason[] = []
    ctx.on('session/event', (_s, event) => { if (event.type === 'turn/end') reasons.push(event.data.reason) })

    send(agent, 'go')
    await new Promise(r => setTimeout(r, 30))
    expect(agent.status).toBe('running')
    send(agent, 'queued tail')
    agent.cancel({ kind: 'user' })
    await waitForIdle(ctx, agent)

    expect(reasons).toEqual([{ kind: 'aborted' }])
    expect(userTexts(agent)).toEqual(['go'])
    expect(agent.session.events.filter(event => event.type === 'turn/start')).toHaveLength(1)
    expect(adapter.requests).toHaveLength(1)
  })

  it('cancel from an assistant/message observer skips execution but balances replay', async () => {
    const adapter = new MockAdapter([
      toolCallResponse('c1', 'danger', {}),
      textResponse('recovered after cancellation'),
    ])
    const ctx = await harness(adapter)
    let executions = 0
    ctx.tools.register(defineContentToolFixture({
      name: 'danger',
      description: 'must not run after cancellation',
      parameters: {},
      async execute() {
        executions += 1
        return [{ type: 'text', text: 'ran' }]
      },
    }))
    const agent = ctx.agentLoop.create(SessionId('cancel-after-assistant-message'), { provider: 'mock', model: 'mock' })
    const dispose = ctx.on('session/event', (session, event) => {
      if (session === agent.session && event.type === 'assistant/message') {
        agent.cancel({ kind: 'user' })
      }
    })

    const reasons: TurnEndReason[] = []
    ctx.on('session/event', (_session, event) => { if (event.type === 'turn/end') reasons.push(event.data.reason) })

    send(agent, 'go')
    await waitForIdle(ctx, agent)
    dispose()

    expect(executions).toBe(0)
    expect(reasons).toEqual([{ kind: 'aborted' }])
    const call = agent.session.events.find(event => event.type === 'tool/call')
    const result = agent.session.events.find(event => event.type === 'tool/result')
    expect(call?.type === 'tool/call' ? call.data.callId : undefined).toBe('c1')
    expect(result?.type === 'tool/result' ? result.data : undefined).toMatchObject({
      callId: 'c1',
      isError: true,
      error: { name: 'AbortError', code: TOOL_ABORTED_BEFORE_DISPATCH },
    })

    send(agent, 'continue safely')
    await waitForIdle(ctx, agent)
    const replayedResult = adapter.requests[1]!.messages
      .flatMap(message => message.content)
      .find(block => block.type === 'tool-result')
    expect(replayedResult).toMatchObject({ toolCallId: 'c1', isError: true })
    expect(reasons).toEqual([
      { kind: 'aborted' },
      { kind: 'completed' },
    ])
  })

  it('a prompt sent AFTER a cancelled turn settles runs normally (marker reset)', async () => {
    const adapter = new MockAdapter(['hang', textResponse('second reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // First turn hangs; cancel it mid-step.
    send(agent, 'first')
    await new Promise(r => setTimeout(r, 30))
    agent.cancel({ kind: 'user' })
    await waitForIdle(ctx, agent)

    // The marker must have been reset after the cancelled turn — a fresh prompt
    // runs to completion rather than being dropped by a stale marker.
    send(agent, 'second')
    await waitForIdle(ctx, agent)

    expect(userTexts(agent)).toContain('second')
    // The second turn completed (its reply was streamed).
    const reasons = agent.session.events.filter(e => e.type === 'turn/end')
    expect(reasons.length).toBe(2)
  })

  it('cancel from a synchronous turn/start session-event listener drops the step (step-start window)', async () => {
    const adapter = new MockAdapter([textResponse('should not stream')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // A turn/start listener fires before a step controller exists, so the
    // turn-scoped marker—not step abort—must drop the pending step.
    let streamed = false
    ctx.on('session/event', (_s, event) => { if (event.type === 'assistant/chunk') streamed = true })
    const dispose = ctx.on('session/event', (session, event) => {
      if (session === agent.session && event.type === 'turn/start') agent.cancel({ kind: 'user' })
    })

    const reasons: TurnEndReason[] = []
    ctx.on('session/event', (_s, event) => { if (event.type === 'turn/end') reasons.push(event.data.reason) })

    send(agent, 'go')
    await waitForIdle(ctx, agent)
    dispose()

    // No step streamed (the model never ran), and the turn ended aborted with
    // the caller's cause — the marker carries `cancel(cause)` through even
    // though no AbortController observed it in this window.
    expect(streamed).toBe(false)
    expect(reasons).toEqual([{ kind: 'aborted' }])
  })

  it('cancel from a synchronous step/start session-event listener drops the step (post-step-start window)', async () => {
    const adapter = new MockAdapter([textResponse('should not stream')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // A step/start session-event listener fires AFTER step/start is appended
    // (and after the pre-step seam), so cancelling there lands in the SECOND
    // cancel check (the one that must closeStep() to balance the already-open
    // step) — distinct from a turn-start cancel, caught before the step opens.
    let streamed = false
    ctx.on('session/event', (_s, event) => { if (event.type === 'assistant/chunk') streamed = true })
    const dispose = ctx.on('session/event', (session, event) => {
      if (session === agent.session && event.type === 'step/start') agent.cancel({ kind: 'user' })
    })

    const reasons: TurnEndReason[] = []
    ctx.on('session/event', (_s, event) => { if (event.type === 'turn/end') reasons.push(event.data.reason) })

    send(agent, 'go')
    await waitForIdle(ctx, agent)
    dispose()

    // No step streamed, the turn ended with the coarse aborted outcome, and the
    // log is balanced (the open step was closed by the cancel branch).
    expect(streamed).toBe(false)
    expect(reasons).toEqual([{ kind: 'aborted' }])
    const types = agent.session.events.map(e => e.type)
    expect(types.filter(t => t === 'step/start').length).toBe(types.filter(t => t === 'step/end').length)
  })

  it('disposal from a synchronous step/start session-event listener closes the open step as disposed', async () => {
    const adapter = new MockAdapter([textResponse('should not stream')])
    const ctx = new Context()
    await ctx.plugin(LlmService)
    await ctx.plugin(SessionStore)
    await ctx.plugin(SystemPrompt)
    await ctx.plugin(ToolRegistry)
    await ctx.plugin(AgentRegistry)
    await ctx.plugin(AgentLoop, { agents: [] })
    ctx.llm.registerAdapter(['mock'], adapter)

    const handle = await ctx.agents.create({
      sessionId: SessionId('dispose-step-start-session'),
      agentOptions: { provider: 'mock', model: 'mock' },
    })
    const agent = handle.agent

    let disposalDone: Promise<void> | undefined
    let streamed = false
    ctx.on('session/event', (_s, event) => { if (event.type === 'assistant/chunk') streamed = true })
    ctx.on('session/event', (session, event) => {
      if (session === agent.session && event.type === 'step/start') disposalDone = handle.dispose()
    })

    send(agent, 'go')
    await disposalDone
    await driverDone(agent)

    expect(streamed).toBe(false)
    expect(adapter.requests).toHaveLength(0)
    const turnEnd = agent.session.events.findLast(e => e.type === 'turn/end')
    expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'disposed' })
    const types = agent.session.events.map(e => e.type)
    expect(types.filter(t => t === 'step/start').length).toBe(types.filter(t => t === 'step/end').length)
  })

  it('cancel during the stopping window ends the turn aborted and runs no further step', async () => {
    const adapter = new MockAdapter([textResponse('one'), textResponse('two')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    let steps = 0
    const reasons: TurnEndReason[] = []
    ctx.on('session/event', (_session, event) => {
      if (event.type === 'step/start') steps += 1
      if (event.type === 'turn/end') reasons.push(event.data.reason)
    })

    let cancelled = false
    ctx.on('agent/turn-stopping', (subject) => {
      if (subject === agent && !cancelled) {
        cancelled = true
        agent.cancel({ kind: 'user' })
      }
    })

    send(agent, 'go')
    await waitForIdle(ctx, agent)

    // Only ONE step ran (the second was cancelled in the stopping window),
    // and the shared turn signal classified the durable outcome as aborted.
    expect(steps).toBe(1)
    expect(reasons).toEqual([{ kind: 'aborted' }])
  })

  it('cancel from a synchronous agent/status(running) listener drops the turn (window 2)', async () => {
    const adapter = new MockAdapter([textResponse('should not run')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    // `agent/status` is synchronous, so cancellation can land after the first
    // pre-step check; the second check must drop the now-empty turn.
    let streamed = false
    ctx.on('session/event', (_s, event) => { if (event.type === 'assistant/chunk') streamed = true })
    const dispose = ctx.on('agent/status', (subject, status) => {
      if (subject === agent && status === 'running') agent.cancel({ kind: 'user' })
    })

    send(agent, 'go')
    await waitForIdle(ctx, agent)
    dispose()

    // No turn opened, no step streamed, and a later prompt still runs (the marker
    // was reset).
    expect(streamed).toBe(false)
    expect(agent.session.events.some(e => e.type === 'turn/start')).toBe(false)
  })

  it('window 2: whenIdle() does NOT resolve early when a running listener cancels then queues replacement work', async () => {
    // Cancellation must not settle idle while replacement work remains queued.
    const adapter = new MockAdapter([textResponse('A reply'), textResponse('B reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    let replaced = false
    const dispose = ctx.on('agent/status', (subject, status) => {
      if (subject !== agent || status !== 'running' || replaced) return
      replaced = true
      agent.cancel({ kind: 'user' })
      send(agent, 'B')
    })

    send(agent, 'A')
    const idle = agent.whenIdle()
    await idle
    dispose()

    // whenIdle() resolved only AFTER B's turn ran: B's user message + a turn/end
    // are in the log, and A was dropped.
    expect(userTexts(agent)).toContain('B')
    expect(userTexts(agent)).not.toContain('A')
    expect(agent.session.events.some(e => e.type === 'turn/end')).toBe(true)
  })

  it('whenIdle() does NOT resolve early when a new prompt is queued during a pre-step cancel', async () => {
    // The subtle race: a whenIdle() waiter is registered for prompt A; cancel() clears A;
    // prompt B is queued before the loop resumes from the idle wait.
    const adapter = new MockAdapter([textResponse('A reply'), textResponse('B reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    send(agent, 'A')           // queues A (status still idle, loop microtask pending)
    const idle = agent.whenIdle() // registers a waiter (idle + hasQueued → no fast path)
    agent.cancel({ kind: 'user' })     // arms marker, clears A
    send(agent, 'B')           // B races in before the loop resumes

    // whenIdle() must resolve only after B's turn fully ran — by which point B's user message
    // and a turn/end are in the log.
    await idle
    expect(userTexts(agent)).toContain('B')
    expect(agent.session.events.some(e => e.type === 'turn/end')).toBe(true)
    // A was dropped (never ran); only B's turn is recorded.
    expect(userTexts(agent)).not.toContain('A')
  })

  it("cancel clears the turn's steering — it is not re-enqueued as a fresh turn", async () => {
    const adapter = new MockAdapter(['hang'])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })

    send(agent, 'go')
    await new Promise(r => setTimeout(r, 30))
    expect(agent.status).toBe('running')
    // Steer (joins the running turn's steering FIFO), then cancel: the steering
    // must be dropped, NOT re-enqueued as a new queued turn.
    agent.steer({ content: [{ type: 'text', text: 'steer text' }], source: { kind: 'user' } })
    agent.cancel({ kind: 'user' })
    await waitForIdle(ctx, agent)

    // After the cancelled turn settles, the agent is idle with NO follow-up turn
    // started from the dropped steering.
    await new Promise(r => setTimeout(r, 30))
    expect(agent.status).toBe('idle')
    const turnStarts = agent.session.events.filter(e => e.type === 'turn/start')
    expect(turnStarts.length).toBe(1) // only the original (cancelled) turn
    // The steering text was dropped — it never reached the log.
    const flat = agent.session.events
      .filter(e => e.type === 'steering/message')
      .flatMap(e => e.type === 'steering/message' ? e.data.content : [])
      .flatMap(b => b.type === 'text' ? [b.text] : [])
    expect(flat).not.toContain('steer text')
  })

  it('keeps replacement work queued synchronously by an abort observer', async () => {
    const adapter = new MockAdapter(['hang', textResponse('replacement reply')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('abort-observer-replacement'), { provider: 'mock', model: 'mock' })

    send(agent, 'original')
    await expect.poll(() => adapter.requests.length).toBe(1)
    const signal = adapter.requests[0]?.signal
    if (signal === undefined) throw new Error('model request omitted its turn signal')
    signal.addEventListener('abort', () => { send(agent, 'replacement') }, { once: true })
    const idle = waitForIdle(ctx, agent)
    agent.cancel({ kind: 'user' })
    await Promise.race([
      idle,
      new Promise((_resolve, reject) => {
        setTimeout(() => {
          reject(new Error(`replacement did not settle: ${JSON.stringify({
            status: agent.status,
            requests: adapter.requests.length,
            users: userTexts(agent),
            events: agent.session.events.map(event => event.type),
          })}`))
        }, 1000)
      }),
    ])

    expect(adapter.requests).toHaveLength(2)
    expect(userTexts(agent)).toEqual(['original', 'replacement'])
    const reasons = agent.session.events
      .filter(event => event.type === 'turn/end')
      .map(event => event.type === 'turn/end' ? event.data.reason : undefined)
    expect(reasons).toEqual([{ kind: 'aborted' }, { kind: 'completed' }])
  })

  it('keeps the first typed cause for an active turn and detaches the runtime reason', async () => {
    const adapter = new MockAdapter(['hang'])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId('typed-first-wins'), { provider: 'mock', model: 'mock' })
    const supplied: { kind: 'parent' | 'user' } = { kind: 'parent' }

    send(agent, 'go')
    await expect.poll(() => adapter.requests.length).toBe(1)
    agent.cancel(supplied)
    supplied.kind = 'user'
    agent.cancel({ kind: 'user' })
    await waitForIdle(ctx, agent)

    const runtimeReason: unknown = adapter.requests[0]?.signal?.reason
    expect(runtimeReason).toEqual({ kind: 'parent' })
    expect(runtimeReason).not.toBe(supplied)
    expect(Object.isFrozen(runtimeReason)).toBe(true)
    const turnEnd = agent.session.events.findLast(event => event.type === 'turn/end')
    expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted' })
  })

  it('preserves the first user cancellation when lifecycle teardown races it', async () => {
    const adapter = new MockAdapter(['hang'])
    const ctx = await harness(adapter)
    const handle = await ctx.agents.create({
      sessionId: SessionId('cancel-dispose-race'),
      agentOptions: { provider: 'mock', model: 'mock' },
    })
    const { agent } = handle

    send(agent, 'go')
    await expect.poll(() => adapter.requests.length).toBe(1)
    agent.cancel({ kind: 'user' })
    await handle.dispose()

    const turnEnd = agent.session.events.findLast(event => event.type === 'turn/end')
    expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted' })
  })

  it.each([
    'prompt-submit',
    'system-prompt',
    'step',
    'request',
    'stopping',
    'tool',
  ] as const)('lets a cooperative %s boundary settle from the explicit turn signal', async (stage) => {
    const adapter = new MockAdapter(stage === 'tool'
      ? [toolCallResponse('blocked-tool', 'blocked', {})]
      : [textResponse('done')])
    const ctx = await harness(adapter)
    const agent = ctx.agentLoop.create(SessionId(`cooperative-${stage}`), { provider: 'mock', model: 'mock' })
    const started = Promise.withResolvers<undefined>()
    const blockUntilAbort = async (signal: AbortSignal): Promise<void> => {
      started.resolve(undefined)
      if (signal.aborted) return
      await new Promise<void>((resolve) => {
        signal.addEventListener('abort', () => { resolve() }, { once: true })
      })
    }

    switch (stage) {
      case 'prompt-submit':
        ctx.on('agent/prompt-submit', async (subject, _content, _source, signal, next) => {
          if (subject === agent) await blockUntilAbort(signal)
          return next()
        })
        break
      case 'system-prompt':
        ctx.on('system-prompt/assemble', async (_assembly, context, next) => {
          if (context.agent === agent) {
            if (context.signal === undefined) throw new Error('turn assembly omitted its signal')
            await blockUntilAbort(context.signal)
          }
          return next()
        })
        break
      case 'step':
        ctx.on('agent/step', async (subject, _turn, _step, signal) => {
          if (subject === agent) await blockUntilAbort(signal)
        })
        break
      case 'request':
        ctx.on('agent/request', async (subject, _turn, _step, signal, next) => {
          if (subject === agent) await blockUntilAbort(signal)
          return next()
        })
        break
      case 'stopping':
        ctx.on('agent/turn-stopping', async (subject, _turn, signal) => {
          if (subject === agent) await blockUntilAbort(signal)
        })
        break
      case 'tool':
        ctx.tools.register(defineContentToolFixture({
          name: 'blocked',
          description: 'wait for cancellation',
          parameters: {},
          execute: async (_args, exec) => {
            if (exec.signal === undefined) throw new Error('tool execution omitted its signal')
            await blockUntilAbort(exec.signal)
            return [{ type: 'text', text: 'cancelled' }]
          },
        }))
        break
    }

    send(agent, 'go')
    await started.promise
    const idle = agent.whenIdle()
    agent.cancel({ kind: 'user' })
    await idle
    const turnEnd = agent.session.events.findLast(event => event.type === 'turn/end')
    if (stage === 'prompt-submit') {
      expect(turnEnd).toBeUndefined()
    } else {
      expect(turnEnd?.type === 'turn/end' && turnEnd.data.reason).toEqual({ kind: 'aborted' })
    }
    await ctx.fiber.dispose()
  })
})