deepseek-harness/packages/client/runtime/tests/session.spec.ts

/**
 * Session orchestration: drive the object through contract calls and injected
 * frames (open → prompt → stream → finalize → cancel → resync) and assert the
 * ConversationSnapshot it settles into. Reference stability is asserted with
 * toBe/not.toBe — it is the React.memo/uSES contract, equal-value output is not
 * enough.
 */

import { describe, expect, it, vi } from 'vitest'
import type { SessionEvent } from '@deepseek-ai/dsh-session/types'
import type { SessionId } from '@deepseek-ai/dsh-client-connection/client'
import { Session } from '../src/client/sessions/session.ts'
import { FakeApiClient, deferred, err, ok } from './fake-api.ts'
import { entries, ev, plainTurn } from './event-script.ts'

const at = (seq: number, e: Record<string, unknown>): SessionEvent =>
  ({ seq, time: 1_700_000_000_000 + seq, ...e }) as unknown as SessionEvent

const SID = 'fk-s1' as SessionId

function makeSession(api = new FakeApiClient()): { api: FakeApiClient; session: Session } {
  return { api, session: new Session(SID, api) }
}

function histResponse(events: SessionEvent[], hasMore = false) {
  // history now returns HistoryEntry[] ({event, view?}); these tests are view-less.
  return Promise.resolve(ok({ events: entries(events) as never[], hasMore }))
}

describe('open', () => {
  it('installs the tail page: cold → loading → open with window and nodes in place', async () => {
    const { api, session } = makeSession()
    const page = plainTurn(10, 3, '问', '答')
    api.onHistory = () => histResponse(page, true)
    expect(session.getSnapshot().openState).toBe('cold')
    const opening = session.open()
    expect(session.getSnapshot().openState).toBe('loading')
    await opening
    const snapshot = session.getSnapshot()
    expect(snapshot.openState).toBe('open')
    expect(snapshot.hasMore).toBe(true)
    expect(snapshot.nodes.map(n => n.kind)).toEqual(['user', 'assistant'])
  })

  it('is idempotent: concurrent opens share one history call, reopening when open is a no-op', async () => {
    const { api, session } = makeSession()
    await Promise.all([session.open(), session.open()])
    await session.open()
    expect(api.callsOf('session.history')).toHaveLength(1)
  })

  it('lands an error result in openState=error with the RpcError kept', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => Promise.resolve(err({ code: 'session-not-found', message: 'gone', details: { sessionId: SID } }))
    await session.open()
    const snapshot = session.getSnapshot()
    expect(snapshot.openState).toBe('error')
    expect(snapshot.openError?.code).toBe('session-not-found')
  })

  it('folds a transport throw into openState=error / internal', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => Promise.reject(new Error('socket died'))
    await session.open()
    expect(session.getSnapshot().openState).toBe('error')
    expect(session.getSnapshot().openError).toMatchObject({ code: 'internal', message: 'socket died' })
  })

  it('stitches live frames arriving while history is pending, dropping the page overlap', async () => {
    const { api, session } = makeSession()
    const gate = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => gate.promise
    const opening = session.open()
    // Three live frames land mid-open; seq 15 overlaps the page tail (page covers 10..15).
    const page = plainTurn(10, 0, '早', '安')
    session.handleMuxEnvelope('r1' as never, { type: 'session/event', sessionId: SID, event: ev.turnStart(15, 1) })
    session.handleMuxEnvelope('r2' as never, { type: 'session/event', sessionId: SID, event: ev.user(16, '插进来的') })
    gate.resolve(ok({ events: entries(page) as never[], hasMore: false }))
    await opening
    const seqs = session.getSnapshot().nodes.map(n => n.seq)
    // Overlapping seq-15 frame (== page tail turn/end) was dropped; 16 appended once.
    expect(seqs).toEqual([11, 13, 16])
  })
})

describe('live event path', () => {
  async function opened(events: SessionEvent[] = plainTurn(0, 0, 'a', 'b')) {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(events)
    await session.open()
    return { api, session }
  }

  it('drops replayed frames at or below the window tail', async () => {
    const { session } = await opened()
    const before = session.getSnapshot()
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.user(3, '重放') })
    await Promise.resolve()
    expect(session.getSnapshot().nodes).toEqual(before.nodes)
  })

  it('accumulates chunks into partial, then finalize swaps partial out as the node lands', async () => {
    const { session } = await opened()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.user(7, '流式问'))
    feed(ev.chunkStart(8, 1))
    feed(ev.chunkText(9, 1, '半截'))
    let snapshot = session.getSnapshot()
    expect(snapshot.partial).toMatchObject({ turn: 1, blocks: [{ kind: 'text', text: '半截' }] })
    feed(ev.chunkText(10, 1, '回复'))
    expect(session.getSnapshot().partial?.blocks).toEqual([{ kind: 'text', text: '半截回复' }])
    feed(ev.assistant(11, 1, '半截回复'))
    feed(ev.turnEnd(12, 1))
    snapshot = session.getSnapshot()
    expect(snapshot.partial).toBeNull()
    const last = snapshot.nodes.at(-1)
    expect(last).toMatchObject({ kind: 'assistant', blocks: [{ kind: 'text', text: '半截回复' }] })
    expect((last as { interrupted?: true }).interrupted).toBeUndefined()
  })

  it('freezes an unfinalized partial into an interrupted node on turn/end (cancel path)', async () => {
    const { session } = await opened()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.user(7, '要被打断的'))
    feed(ev.chunkStart(8, 1))
    feed(ev.chunkText(9, 1, '说到一半'))
    feed(ev.turnEnd(10, 1, 'cancelled')) // no assistant/message ever arrives
    const snapshot = session.getSnapshot()
    expect(snapshot.partial).toBeNull()
    const frozen = snapshot.nodes.at(-1)
    expect(frozen).toMatchObject({ kind: 'assistant', interrupted: true, blocks: [{ kind: 'text', text: '说到一半' }] })
    // Ordered inside the flow: after the user message (seq 7), before any later turn.
    expect((frozen as { seq: number }).seq).toBeGreaterThan(7)
  })

  it('tracks tool calls in runningCalls and converts orphans to interrupted tool-result cards on turn/end', async () => {
    const { session } = await opened()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.toolCall(7, 1, 'c1', 'echo', '{"a":1}'))
    expect(session.getSnapshot().runningCalls).toMatchObject([{ callId: 'c1', name: 'echo' }])
    feed(ev.toolResult(8, 1, 'c1', 'ECHO'))
    expect(session.getSnapshot().runningCalls).toEqual([])
    // Second call never resolves: turn/end freezes it as an error card.
    feed(ev.toolCall(9, 1, 'c2', 'slow_tool', '{}'))
    feed(ev.turnEnd(10, 1, 'cancelled'))
    const snapshot = session.getSnapshot()
    expect(snapshot.runningCalls).toEqual([])
    expect(snapshot.nodes.at(-1)).toMatchObject({
      kind: 'tool-result', callId: 'c2', isError: true, error: { code: 'interrupted' },
    })
  })

  it('repairs a seq gap by repulling the tail page instead of appending a hole', async () => {
    const { api, session } = await opened(plainTurn(0, 0, 'a', 'b')) // tail seq = 5
    const repaired = [...plainTurn(0, 0, 'a', 'b'), ...plainTurn(6, 1, 'c', 'd')]
    api.onHistory = () => histResponse(repaired)
    // seq 9 with tail 5 → gap; the event detours to the buffer and one history refetch fires.
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.assistant(9, 1, 'd') })
    await vi.waitFor(() => {
      expect(api.callsOf('session.history').length).toBe(2)
    })
    await Promise.resolve()
    const seqs = session.getSnapshot().nodes.map(n => n.seq)
    expect(seqs).toEqual([1, 3, 7, 9]) // both turns' user/assistant, no hole, no duplicate 9
  })
})

describe('paging', () => {
  it('prepends an older page and keeps seq continuity', async () => {
    const older = plainTurn(0, 0, '旧问', '旧答')
    const newer = plainTurn(6, 1, '新问', '新答')
    const { api, session } = makeSession()
    api.onHistory = payload => payload.beforeSeq === undefined
      ? histResponse(newer, true)
      : histResponse(older, false)
    await session.open()
    await session.loadOlder()
    const snapshot = session.getSnapshot()
    expect(api.callsOf('session.history')).toMatchObject([{}, { beforeSeq: 6 }].map(p => ({ sessionId: SID, ...p })))
    expect(snapshot.hasMore).toBe(false)
    expect(snapshot.nodes.map(n => n.seq)).toEqual([1, 3, 7, 9])
  })

  it('drops a discontinuous older page fail-soft (window unchanged, hasMore cleared)', async () => {
    const { api, session } = makeSession()
    api.onHistory = payload => payload.beforeSeq === undefined
      ? histResponse(plainTurn(10, 1, '新', '页'), true)
      : histResponse(plainTurn(0, 0, '断', '层'), true) // tail seq 5, but baseSeq is 10 → hole
    const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => undefined)
    try {
      await session.open()
      const nodesBefore = session.getSnapshot().nodes
      await session.loadOlder()
      const snapshot = session.getSnapshot()
      expect(snapshot.nodes).toEqual(nodesBefore)
      expect(snapshot.hasMore).toBe(false)
    } finally {
      errorSpy.mockRestore()
    }
  })

  it('ignores loadOlder while one is in flight (single request)', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(6, 1, 'x', 'y'), true)
    await session.open()
    const gate = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => gate.promise
    const first = session.loadOlder()
    const second = session.loadOlder()
    gate.resolve(ok({ events: entries(plainTurn(0, 0, 'a', 'b')) as never[], hasMore: false }))
    await Promise.all([first, second])
    expect(api.callsOf('session.history')).toHaveLength(2) // open + one page, not two
  })
})

describe('prompt and cancel errors', () => {
  it('sends content through session.prompt with the mode passed through', async () => {
    const { api, session } = makeSession()
    const result = await session.prompt([{ type: 'text', text: '要发的' }], 'queue')
    expect(result.ok).toBe(true)
    expect(api.callsOf('session.prompt')).toMatchObject([{ sessionId: SID, mode: 'queue', content: [{ type: 'text', text: '要发的' }] }])
  })

  it('business failure lands in promptError with op=send', async () => {
    const { api, session } = makeSession()
    api.onPrompt = () => Promise.resolve(err({ code: 'agent-busy', message: 'busy', details: { reason: 'x' } }))
    const result = await session.prompt([{ type: 'text', text: '失败的' }], 'queue')
    expect(result.ok).toBe(false)
    expect(session.getSnapshot().promptError).toMatchObject({ op: 'send', error: { code: 'agent-busy' } })
  })

  it('lands cancel failures in promptError with op=stop', async () => {
    const { api, session } = makeSession()
    api.onCancel = () => Promise.reject(new Error('cancel transport down'))
    const result = await session.cancel()
    expect(result.ok).toBe(false)
    expect(session.getSnapshot().promptError).toMatchObject({ op: 'stop', error: { code: 'internal' } })
  })
})

describe('pending interactions', () => {
  it('adds approval/question on requested and removes them on resolved', async () => {
    const { session } = makeSession()
    session.handleMuxEnvelope('ra' as never, { type: 'approval/requested', sessionId: SID, approvalId: 'ap1' as never, toolName: 'rm' })
    session.handleMuxEnvelope('rq' as never, { type: 'question/requested', sessionId: SID, questions: [] })
    expect(session.getSnapshot().pending.map(p => p.kind).sort()).toEqual(['approval', 'question'])
    session.handleMuxEnvelope('rx' as never, { type: 'approval/resolved', sessionId: SID, approvalId: 'ap1' as never, outcome: 'approved' as never })
    session.handleMuxEnvelope('ry' as never, { type: 'question/resolved', sessionId: SID, questionRpcId: 'rq' as never, outcome: 'answered' })
    expect(session.getSnapshot().pending).toEqual([])
  })

  it('mints waits whose respond() backfills the requested rpcId into the client-response envelope', async () => {
    const { api, session } = makeSession()
    session.handleMuxEnvelope('rq-answer' as never, { type: 'question/requested', sessionId: SID, questions: [] })
    const wait = session.getSnapshot().pending[0]!
    expect(wait).toMatchObject({ kind: 'question', key: 'q:rq-answer', sessionId: SID, payload: { questions: [] } })
    const receipt = await wait.respond({
      ok: true,
      value: { sessionId: SID, answer: { answers: [{ id: 'mode', selected: ['Fast'] }] } },
    })
    expect(receipt).toEqual({ accepted: true })
    expect(api.callsOf('respond')).toEqual([{
      type: 'client-response', rpcId: 'rq-answer',
      result: {
        ok: true,
        value: { sessionId: SID, answer: { answers: [{ id: 'mode', selected: ['Fast'] }] } },
      },
    }])
  })

  it('settles the wait on the authoritative resolved frame: respond() then throws synchronously', async () => {
    const { api, session } = makeSession()
    session.handleMuxEnvelope('rq1' as never, { type: 'question/requested', sessionId: SID, questions: [] })
    const wait = session.getSnapshot().pending[0]!
    session.handleMuxEnvelope('ry' as never, { type: 'question/resolved', sessionId: SID, questionRpcId: 'rq1' as never, outcome: 'answered' })
    expect(session.getSnapshot().pending).toEqual([])
    expect(() => wait.respond({ ok: false, error: { code: 'internal', message: 'x', details: {} } }))
      .toThrow('already settled')
    expect(api.callsOf('respond')).toEqual([])
  })
})

describe('remaining branches', () => {
  it('prompt transport throw folds to internal promptError', async () => {
    const { api, session } = makeSession()
    api.onPrompt = () => Promise.reject(new Error('prompt wire down'))
    const result = await session.prompt([{ type: 'text', text: 'x' }], 'queue')
    expect(result.ok).toBe(false)
    expect(session.getSnapshot().promptError).toMatchObject({ op: 'send', error: { code: 'internal', message: 'prompt wire down' } })
  })

  it('cancel business error also lands op=stop promptError', async () => {
    const { api, session } = makeSession()
    api.onCancel = () => Promise.resolve(err({ code: 'agent-busy', message: 'nope', details: { reason: 'r' } }))
    await session.cancel()
    expect(session.getSnapshot().promptError).toMatchObject({ op: 'stop', error: { code: 'agent-busy' } })
  })

  it('loadOlder guards: not-open/no-hasMore no-op, err result kept window, empty page updates hasMore, throw fail-soft', async () => {
    const { api, session } = makeSession()
    await session.loadOlder() // cold: no-op, zero calls
    expect(api.calls).toEqual([])
    api.onHistory = () => histResponse(plainTurn(6, 1, 'x', 'y'), true)
    await session.open()
    // err result: window unchanged
    api.onHistory = () => Promise.resolve(err({ code: 'internal', message: 'x', details: {} }))
    await session.loadOlder()
    expect(session.getSnapshot().nodes).toHaveLength(2)
    expect(session.getSnapshot().hasMore).toBe(true)
    // empty page: hasMore adopts the response
    api.onHistory = () => histResponse([], false)
    await session.loadOlder()
    expect(session.getSnapshot().hasMore).toBe(false)
    // hasMore false now: further loadOlder is a guard no-op
    const calls = api.calls.length
    await session.loadOlder()
    expect(api.calls.length).toBe(calls)
    // throw path: fail-soft with console.error
    const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => undefined)
    try {
      await session.resync()
      api.onHistory = () => histResponse(plainTurn(6, 1, 'x', 'y'), true)
      await session.resync()
      api.onHistory = () => Promise.reject(new Error('page wire down'))
      await session.loadOlder()
      expect(errorSpy).toHaveBeenCalled()
      expect(session.getSnapshot().loadingOlder).toBe(false)
    } finally {
      errorSpy.mockRestore()
    }
  })

  it('subscribe delivers snapshot-change notifications and unsubscribes', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    let notified = 0
    const unsubscribe = session.subscribe(() => { notified++ })
    await session.open()
    await new Promise(resolve => setTimeout(resolve, 0))
    expect(notified).toBeGreaterThan(0)
    const seen = notified
    unsubscribe()
    session.handleRunning(true) // any snapshot mutation; the listener must stay silent
    await new Promise(resolve => setTimeout(resolve, 0))
    expect(notified).toBe(seen)
  })

  it('subscribed baseline past the window tail triggers the second stitch pull in doOpen', async () => {
    const { api, session } = makeSession()
    const full = [...plainTurn(0, 0, 'a', 'b'), ...plainTurn(6, 1, 'c', 'd')]
    let call = 0
    api.onHistory = () => {
      call++
      return histResponse(call === 1 ? plainTurn(0, 0, 'a', 'b') : full)
    }
    // Baseline arrives before open: lastSeq 11 > first page tail 5 → doOpen repulls once.
    session.handleMuxEnvelope('rs' as never, { type: 'session/subscribed', sessionId: SID, lastSeq: 11 })
    await session.open()
    expect(call).toBe(2)
    expect(session.getSnapshot().nodes.map(n => n.seq)).toEqual([1, 3, 7, 9])
  })

  it('a failed second stitch pull keeps the first window and still opens', async () => {
    const { api, session } = makeSession()
    let call = 0
    api.onHistory = () => {
      call++
      return call === 1
        ? histResponse(plainTurn(0, 0, 'a', 'b'))
        : Promise.resolve(err({ code: 'internal', message: 'stitch pull down', details: {} }))
    }
    session.handleMuxEnvelope('rs' as never, { type: 'session/subscribed', sessionId: SID, lastSeq: 11 })
    await session.open()
    expect(call).toBe(2)
    const snapshot = session.getSnapshot()
    expect(snapshot.openState).toBe('open') // stitch-pull failure is not an open failure
    expect(snapshot.nodes.map(n => n.seq)).toEqual([1, 3]) // first window kept
  })

  it('approval frame with callId/reason keeps the optional fields; duplicate resolved is a no-op', () => {
    const { session } = makeSession()
    session.handleMuxEnvelope('ra' as never, {
      type: 'approval/requested', sessionId: SID, approvalId: 'ap2' as never, toolName: 'rm', callId: 'c1' as never, reason: '危险',
    })
    expect(session.getSnapshot().pending[0]).toMatchObject({ kind: 'approval', payload: { callId: 'c1', reason: '危险' } })
    session.handleMuxEnvelope('rx' as never, { type: 'approval/resolved', sessionId: SID, approvalId: 'ap2' as never, outcome: 'approved' as never })
    session.handleMuxEnvelope('rx2' as never, { type: 'approval/resolved', sessionId: SID, approvalId: 'ap2' as never, outcome: 'approved' as never })
    session.handleMuxEnvelope('ry2' as never, { type: 'question/resolved', sessionId: SID, questionRpcId: 'never-was' as never, outcome: 'cancelled' })
    expect(session.getSnapshot().pending).toEqual([])
  })

  it('ignores unknown mux frame types and repeated running flips (documented defaults)', () => {
    const { session } = makeSession()
    const before = session.getSnapshot()
    session.handleMuxEnvelope('rz' as never, { type: 'future/frame' } as never)
    session.handleRunning(false) // already false: dedup branch
    expect(session.getSnapshot()).toBe(before)
    session.handleRemoved()
    expect(session.getSnapshot().removed).toBe(true)
  })

  it('drops live events while cold/error (no window upkeep)', async () => {
    const { api, session } = makeSession()
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.user(0, '冷态帧') })
    expect(session.getSnapshot().nodes).toEqual([])
    api.onHistory = () => Promise.resolve(err({ code: 'internal', message: 'x', details: {} }))
    await session.open()
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.user(0, '错态帧') })
    expect(session.getSnapshot().nodes).toEqual([])
  })

  it('repairGap failure logs and clears stitching; concurrent gaps coalesce into one repair', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const gate = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    let repairs = 0
    api.onHistory = () => {
      repairs++
      return gate.promise
    }
    const errorSpy = vi.spyOn(console, 'error').mockImplementation(() => undefined)
    try {
      session.handleMuxEnvelope('r1' as never, { type: 'session/event', sessionId: SID, event: ev.user(9, '洞一') })
      session.handleMuxEnvelope('r2' as never, { type: 'session/event', sessionId: SID, event: ev.user(10, '洞二') }) // stitching: detours, no second repair
      expect(repairs).toBe(1)
      gate.reject(new Error('repair wire down'))
      await vi.waitFor(() => { expect(errorSpy).toHaveBeenCalled() })
      // Window unchanged; a later successful repull still lands the buffered frames.
      expect(session.getSnapshot().nodes).toHaveLength(2)
    } finally {
      errorSpy.mockRestore()
    }
  })

  it('freezes only content-bearing partials; a content-free partial is dropped outright', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.chunkStart(7, 1)) // empty text block only, no delta
    feed(ev.turnEnd(8, 1, 'cancelled'))
    const snapshot = session.getSnapshot()
    expect(snapshot.partial).toBeNull()
    expect(snapshot.nodes.filter(n => n.kind === 'assistant' && (n as { interrupted?: true }).interrupted)).toEqual([])
  })

  it('turn/end sweeps only same-turn open calls; other turns keep running', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.toolCall(7, 1, 'turn1-call', 'echo', '{}'))
    feed(ev.toolCall(8, 2, 'turn2-call', 'echo', '{}')) // stray call attributed to a later turn
    feed(ev.turnEnd(9, 1, 'cancelled'))
    const snapshot = session.getSnapshot()
    expect(snapshot.runningCalls.map(c => c.callId)).toEqual(['turn2-call'])
    expect(snapshot.nodes.at(-1)).toMatchObject({ kind: 'tool-result', callId: 'turn1-call', isError: true })
  })

  it('doOpen transport throw of a stale generation is swallowed (generation guard in catch)', async () => {
    const { api, session } = makeSession()
    const stale = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => stale.promise
    const opening = session.open()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    const resynced = session.resync()
    stale.reject(new Error('stale wire'))
    await Promise.all([opening, resynced])
    expect(session.getSnapshot().openState).toBe('open') // stale catch did not write error
  })

  it('drops a stale doOpen whose history resolved successfully after resync superseded it', async () => {
    const { api, session } = makeSession()
    const stale = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => stale.promise
    const opening = session.open()
    api.onHistory = () => histResponse(plainTurn(6, 1, '新', '代'))
    const resynced = session.resync()
    stale.resolve(ok({ events: entries(plainTurn(0, 0, '旧', '代')) as never[], hasMore: false })) // success, but its generation is gone
    await Promise.all([opening, resynced])
    expect(session.getSnapshot().nodes.map(n => n.seq)).toEqual([7, 9]) // only the fresh generation's window
  })

  it('drops a stale stitch pull (second doOpen fetch) superseded mid-flight by resync', async () => {
    const { api, session } = makeSession()
    const secondPull = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    let call = 0
    api.onHistory = () => {
      call++
      if (call === 1) return histResponse(plainTurn(0, 0, 'a', 'b')) // first page: tail 5
      if (call === 2) return secondPull.promise // gap-stitch pull: held
      return histResponse(plainTurn(6, 1, 'c', 'd'))
    }
    session.handleMuxEnvelope('rs' as never, { type: 'session/subscribed', sessionId: SID, lastSeq: 11 })
    const opening = session.open() // triggers the second pull, which parks
    await vi.waitFor(() => { expect(call).toBe(2) })
    const resynced = session.resync()
    secondPull.resolve(ok({ events: entries([...plainTurn(0, 0, 'a', 'b'), ...plainTurn(6, 1, 'c', 'd')]) as never[], hasMore: false }))
    await Promise.all([opening, resynced])
    expect(session.getSnapshot().openState).toBe('open')
  })

  it('drops a gap repair superseded by a full resync while its pull was in flight', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const repairPull = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => repairPull.promise
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.user(9, '洞') }) // starts repairGap
    api.onHistory = () => histResponse(plainTurn(6, 1, 'c', 'd'))
    const resynced = session.resync() // bumps the generation
    repairPull.resolve(ok({ events: entries(plainTurn(0, 0, '旧', '页')) as never[], hasMore: false })) // repair result: stale, dropped
    await resynced
    expect(session.getSnapshot().nodes.map(n => n.seq)).toEqual([7, 9])
  })

  it('successful cancel leaves no promptError; tool/result for an unknown callId is a no-op', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const result = await session.cancel()
    expect(result.ok).toBe(true)
    expect(session.getSnapshot().promptError).toBeNull()
    const callsBefore = session.getSnapshot().runningCalls
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.toolResult(6, 0, 'never-called', 'x') })
    expect(session.getSnapshot().runningCalls).toBe(callsBefore) // callsRev untouched: same reference
  })

  it('freezes a tool-call-only partial (visible through the non-text arm)', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(at(7, { type: 'assistant/chunk', data: { turn: 1, step: 0, chunk: { type: 'tool-call-delta', index: 0, id: 'c1', name: 'echo', argumentsDelta: '{' } } }))
    feed(ev.turnEnd(8, 1, 'cancelled'))
    const frozen = session.getSnapshot().nodes.at(-1)
    expect(frozen).toMatchObject({ kind: 'assistant', interrupted: true, blocks: [{ kind: 'tool-call', callId: 'c1' }] })
  })

  it('dispose is a reserved no-op on resident instances', () => {
    const { session } = makeSession()
    expect(() => { session.dispose() }).not.toThrow()
  })

  it('carries mux-frame views into runningCalls and tool-result nodes, and history-entry views through open', async () => {
    const { api, session } = makeSession()
    const callView = { for: 'call', view: { card: 'generic', title: '历史卡' } }
    api.onHistory = () => Promise.resolve(ok({
      events: [
        ...entries(plainTurn(0, 0, 'a', 'b')),
        { event: ev.toolCall(6, 1, 'h1', 'bash', '{}'), view: callView },
        { event: ev.toolResult(7, 1, 'h1', 'done'), view: { for: 'result', view: { card: 'generic', title: '历史果' } } },
      ] as never[],
      hasMore: false,
    }))
    await session.open()
    expect(session.getSnapshot().nodes.at(-1)).toMatchObject({
      kind: 'tool-result', callView: { title: '历史卡' }, resultView: { title: '历史果' },
    })
    // Live path: the frame's view slot reaches runningCalls, then the result node.
    session.handleMuxEnvelope('rv1' as never, {
      type: 'session/event', sessionId: SID, event: ev.toolCall(8, 2, 'l1', 'write', '{}'),
      view: { for: 'call', view: { card: 'generic', title: '直播卡' } },
    } as never)
    expect(session.getSnapshot().runningCalls).toMatchObject([{ callId: 'l1', callView: { title: '直播卡' } }])
    session.handleMuxEnvelope('rv2' as never, {
      type: 'session/event', sessionId: SID, event: ev.toolResult(9, 2, 'l1', 'ok'),
      view: { for: 'result', view: { card: 'generic', title: '直播果' } },
    } as never)
    expect(session.getSnapshot().nodes.at(-1)).toMatchObject({
      kind: 'tool-result', callView: { title: '直播卡' }, resultView: { title: '直播果' },
    })
  })
})

describe('resync', () => {
  it('rebuilds the window and clears pending; cold instances no-op', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    session.handleMuxEnvelope('ra' as never, { type: 'approval/requested', sessionId: SID, approvalId: 'ap1' as never, toolName: 'rm' })
    api.onHistory = () => histResponse([...plainTurn(0, 0, 'a', 'b'), ...plainTurn(6, 1, 'c', 'd')])
    await session.resync()
    const snapshot = session.getSnapshot()
    expect(snapshot.openState).toBe('open')
    expect(snapshot.pending).toEqual([]) // baseline replay re-sends still-pending frames
    expect(snapshot.nodes).toHaveLength(4)

    const cold = makeSession()
    await cold.session.resync()
    expect(cold.api.calls).toEqual([]) // never opened: no traffic
  })

  it('re-mints a replayed requested frame as a fresh wait with the same key (old reference superseded)', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, 'a', 'b'))
    await session.open()
    session.handleMuxEnvelope('rq-replay' as never, { type: 'question/requested', sessionId: SID, questions: [] })
    const before = session.getSnapshot().pending[0]!
    await session.resync()
    session.handleMuxEnvelope('rq-replay' as never, { type: 'question/requested', sessionId: SID, questions: [] })
    const after = session.getSnapshot().pending[0]!
    expect(after).not.toBe(before)
    expect(after.key).toBe(before.key)
    // Superseded ≠ settled: an in-flight respond on the stale reference still reaches the host.
    await before.respond({ ok: false, error: { code: 'internal', message: 'x', details: {} } })
    expect(api.callsOf('respond')).toMatchObject([{ rpcId: 'rq-replay' }])
  })

  it('drops a stale in-flight open superseded by resync (generation guard)', async () => {
    const { api, session } = makeSession()
    const stale = deferred<Awaited<ReturnType<FakeApiClient['onHistory']>>>()
    api.onHistory = () => stale.promise
    const firstOpen = session.open()
    api.onHistory = () => histResponse(plainTurn(6, 1, '新', '代'))
    const resynced = session.resync()
    stale.reject(new Error('dead connection')) // the doomed pre-disconnect request fails late
    await firstOpen
    await resynced
    const snapshot = session.getSnapshot()
    expect(snapshot.openState).toBe('open') // stale failure did not settle the fresh generation into error
    expect(snapshot.nodes.map(n => n.seq)).toEqual([7, 9])
  })
})

describe('reference stability (the memo contract)', () => {
  it('keeps unchanged node references across an append and swaps the snapshot object', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, '稳', '定'))
    await session.open()
    const before = session.getSnapshot()
    session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event: ev.user(6, '追加') })
    const after = session.getSnapshot()
    expect(after).not.toBe(before) // top-level swap on change
    expect(after.nodes[0]).toBe(before.nodes[0]) // untouched nodes keep identity
    expect(after.nodes[1]).toBe(before.nodes[1])
    expect(after.nodes).toHaveLength(3)
    // No change → same snapshot reference.
    expect(session.getSnapshot()).toBe(after)
  })

  it('keeps untouched substructure arrays identical across unrelated changes (revision counters)', async () => {
    const { api, session } = makeSession()
    api.onHistory = () => histResponse(plainTurn(0, 0, '底', '座'))
    await session.open()
    const feed = (event: SessionEvent) => { session.handleMuxEnvelope('r' as never, { type: 'session/event', sessionId: SID, event }) }
    feed(ev.turnStart(6, 1))
    feed(ev.toolCall(7, 1, 'c1', 'echo', '{}'))
    session.handleMuxEnvelope('ra' as never, { type: 'approval/requested', sessionId: SID, approvalId: 'ap1' as never, toolName: 'rm' })
    const before = session.getSnapshot()
    // A chunk storm touches partial/nodes only: runningCalls and pending must keep identity.
    feed(ev.chunkStart(8, 1))
    feed(ev.chunkText(9, 1, '与工具无关的流式'))
    const after = session.getSnapshot()
    expect(after).not.toBe(before)
    expect(after.runningCalls).toBe(before.runningCalls)
    expect(after.pending).toBe(before.pending)
    // And a mutation on the tracked domain swaps that array.
    feed(ev.toolResult(10, 1, 'c1', 'ECHO'))
    const resolved = session.getSnapshot()
    expect(resolved.runningCalls).not.toBe(after.runningCalls)
    expect(resolved.pending).toBe(after.pending)
  })
})