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import { describe, expect, it } from 'vitest'
import { Context } from '@deepseek-ai/cordis'
import { toolPairingBalancedAfter, toolPairingBalancedBefore } from '@deepseek-ai/dsh-compaction'
import { createUserMessage, createSystemMessage, CONTEXT_WINDOW_EXCEEDED_CODE, LlmError, resolveRetryPolicy , createMessage } from '@deepseek-ai/dsh-llm'
import type { ContentBlock, GenerateOptions, LlmResolvedModelInfo, ResolvedRetryPolicy, StreamChunk } from '@deepseek-ai/dsh-llm'
import { ToolCallId, LlmAdapter } from '@deepseek-ai/dsh-llm'
import { defineContentToolFixture } from '@deepseek-ai/dsh-tools'
import type { Agent } from '@deepseek-ai/dsh-agent'
import AgentLoop from '@deepseek-ai/dsh-agent-loop'
import { mountAgentLoopTestDependencies } from '@deepseek-ai/dsh-agent-loop-testkit'
import InvariantRegistry from '@deepseek-ai/dsh-invariants'
import * as SessionInvariant from '@deepseek-ai/dsh-session/invariant'
import * as AgentInvariant from '@deepseek-ai/dsh-agent/invariant'
import * as AgentLoopInvariant from '@deepseek-ai/dsh-agent-loop/invariant'
import { BasicCompactionEngine } from '@deepseek-ai/dsh-compaction-basic'
import TokenMeter from '@deepseek-ai/dsh-token-meter'
import * as LlmRetry from '@deepseek-ai/dsh-llm-retry'
import { Session, SessionId, type SessionEvent, type SurfaceEvent } from '@deepseek-ai/dsh-session'

/**
 * CBR-001 regression through the real loop. A replacement checkpoint has a high
 * log seq at the surface head and carries no tool pair, so both adjacent cuts
 * must be safe and re-compacting that checkpoint alone must succeed. This pins
 * surface-position semantics rather than raw-log scanning.
 */

class ReproCompactionEngine extends BasicCompactionEngine {
  override async summarize(): Promise<{ summary: ContentBlock[]; provider: string; model: string }> {
    return {
      summary: [{ type: 'text', text: 'CHECKPOINT SUMMARY' }],
      provider: 'mock',
      model: 'stub',
    }
  }
}

/** Each call emits one tool-call until exhausted, then a final text answer. */
class StepwiseToolAdapter extends LlmAdapter {
  calls = 0
  constructor(private toolSteps: number) {
    super()
  }

  override resolveModel(provider: string, model: string): Promise<LlmResolvedModelInfo> {
    return Promise.resolve({
      provider,
      id: model,
      name: model,
      context: { contextWindow: 400 },
    })
  }

  async * stream(_options: GenerateOptions): AsyncIterable<StreamChunk> {
    const n = this.calls
    this.calls += 1
    if (n < this.toolSteps) {
      const id = ToolCallId(`c${n}`)
      const args = `{"i":${n}}`
      yield { type: 'block-start', index: 0, blockType: 'text' }
      yield { type: 'block-end', index: 0, block: { type: 'text', text: `step ${n}` } }
      yield { type: 'block-start', index: 1, blockType: 'tool-call' }
      yield { type: 'block-end', index: 1, block: { type: 'tool-call', id, name: 'work', arguments: args } }
      yield { type: 'finish', reason: { kind: 'tool-calls' } }
      return
    }
    yield { type: 'block-start', index: 0, blockType: 'text' }
    yield { type: 'block-end', index: 0, block: { type: 'text', text: 'all done' } }
    yield { type: 'finish', reason: { kind: 'stop' } }
  }
}

/** First conversation request overflows, then the rebuilt retry succeeds. */
class OverflowRecoveryAdapter extends LlmAdapter {
  readonly conversationRequests: GenerateOptions[] = []
  readonly summaryRequests: GenerateOptions[] = []
  private readonly retryPolicy = resolveRetryPolicy({
    mode: 'normal',
    maxRetries: 1,
    backoff: { initialDelayMs: 1, maxDelayMs: 1, jitterRatio: 0 },
  }, 'compaction test provider retryPolicy')

  constructor(
    private readonly delivery: 'thrown' | 'in-band',
    private readonly transientAfterOverflow = false,
  ) {
    super()
  }

  override resolveModel(provider: string, model: string): Promise<LlmResolvedModelInfo> {
    return Promise.resolve({
      provider,
      id: model,
      name: model,
      context: { contextWindow: 128 },
    })
  }

  override providerRetryPolicy(_provider: string): ResolvedRetryPolicy {
    return this.retryPolicy
  }

  override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
    // The cache-reusing summarizer replays the conversation prefix and marks
    // its call only by the compaction instruction in the trailing user message.
    const trailing = options.messages.at(-1)?.content
      .map(block => (block.type === 'text' ? block.text : ''))
      .join('') ?? ''
    if (trailing.includes('acting as a compaction engine')) {
      this.summaryRequests.push(options)
      yield { type: 'block-start', index: 0, blockType: 'text' }
      yield { type: 'block-end', index: 0, block: { type: 'text', text: 'RECOVERY CHECKPOINT' } }
      yield { type: 'finish', reason: { kind: 'stop' } }
      return
    }

    this.conversationRequests.push(options)
    if (this.conversationRequests.length === 1) {
      if (this.delivery === 'thrown') {
        throw new LlmError('request too large for model context', CONTEXT_WINDOW_EXCEEDED_CODE)
      }
      yield {
        type: 'finish',
        reason: {
          kind: 'error',
          failure: {
            message: 'request too large for model context',
            code: CONTEXT_WINDOW_EXCEEDED_CODE,
          },
        },
      }
      return
    }
    if (this.transientAfterOverflow && this.conversationRequests.length === 2) {
      throw new LlmError('temporary provider outage', 'SERVER')
    }
    yield { type: 'block-start', index: 0, blockType: 'text' }
    yield { type: 'block-end', index: 0, block: { type: 'text', text: 'recovered' } }
    yield { type: 'finish', reason: { kind: 'stop' } }
  }
}

async function mountInvariants(ctx: Context): Promise<void> {
  await ctx.plugin(InvariantRegistry)
  await ctx.plugin(SessionInvariant)
  await ctx.plugin(AgentInvariant)
  await ctx.plugin(AgentLoopInvariant)
}

async function harness(toolSteps: number): Promise<{ ctx: Context; compact: ReproCompactionEngine }> {
  const ctx = new Context()
  await mountAgentLoopTestDependencies(ctx)
  await mountInvariants(ctx)
  await ctx.plugin(AgentLoop, { agents: [] })
  await ctx.plugin(TokenMeter)
  ctx.llm.registerAdapter(['mock'], new StepwiseToolAdapter(toolSteps))
  ctx.tools.register(defineContentToolFixture({
    name: 'work',
    description: 'does work',
    parameters: { i: { type: 'number' } },
    async execute() {
      return [{ type: 'text', text: 'work result' }]
    },
  }))
  // Small window so several tool steps cross the threshold and compaction
  // fires within the runaway turn after enough history can shrink.
  const compact = new ReproCompactionEngine(ctx, {
    auto: true,
    thresholdRatio: 0.5,
    retainTokens: 50,
    maxTokens: 8192,
    compactionRetries: 1,
  })
  return { ctx, compact }
}

function waitForIdle(ctx: Context, agent: Agent): Promise<void> {
  return new Promise((resolve) => {
    const dispose = ctx.on('agent/status', ({ agent: subject, status }) => {
      if (subject === agent && status === 'idle') {
        dispose()
        resolve()
      }
    })
  })
}

function overflowHistorySeed(): readonly SessionEvent[] {
  const session = Session.create(SessionId('overflow-history-seed'))
  for (let turn = 1; turn <= 2; turn += 1) {
    const sentinel = turn === 1 ? 'OLD HISTORY SENTINEL' : 'RECENT HISTORY'
    session.append('turn/start', {
      turn,
    })
    session.append('user/message', createUserMessage({
      content: [{ type: 'text', text: `${sentinel} ${'old context '.repeat(200)}` }],
      source: { kind: 'user' },
    }), { surfaceOp: 'append' })
    session.append('step/start', { turn, step: 1 })
    session.append('assistant/message', {
      stream: [],
      turn,
      step: 1,
      message: createMessage({
        role: 'assistant',
        content: [{ type: 'text', text: `historical response ${turn} ${'detail '.repeat(200)}` }],
        source: {
          kind: 'model',
          ...{ provider: 'mock', model: 'mock' },
        },
      }),
    }, { surfaceOp: 'append' })
    session.append('step/end', { turn, step: 1 })
    session.append('turn/end', { turn, reason: { kind: 'completed' } })
  }
  return session.snapshotEvents()
}

describe('CBR-001: a real-loop checkpoint is a valid boundary on both sides', () => {
  it('uses the model actually routed by agent/request for post-step pressure', async () => {
    const { ctx } = await harness(8)
    ctx.on('agent/request', async (_payload, next) => ({
      ...await next(), provider: 'mock', model: 'mock',
    }))
    try {
      const agent = await ctx.agentLoop.create(SessionId('routed-pressure'), {
        provider: 'unconfigured-agent-fallback',
        model: 'unconfigured-agent-fallback',
      })
      agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do a routed multi-step task' }], source: { kind: 'user' } }))
      await waitForIdle(ctx, agent)

      expect(agent.session.requestHeader()?.config.model).toBe('mock')
      expect(agent.session.snapshotEvents().some(event => event.type === 'compaction/summary')).toBe(true)
      expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
        type: 'turn/end',
        data: { reason: { kind: 'completed' } },
      })
    } finally {
      await ctx.fiber.dispose()
    }
  })

  it('runs automatic pressure between the completed tool step and the next step', async () => {
    const { ctx } = await harness(8)
    try {
      const agent = await ctx.agentLoop.create(SessionId('post-step-order'), { provider: 'mock', model: 'mock' })
      agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do tool work' }], source: { kind: 'user' } }))
      await waitForIdle(ctx, agent)

      const events = agent.session.snapshotEvents()
      const compactStart = events.find(event => event.type === 'compaction/start')
      expect(compactStart).toBeDefined()
      const precedingResult = events.findLast(event =>
        event.type === 'tool/result' && event.seq < compactStart!.seq,
      )
      if (precedingResult?.type !== 'tool/result') throw new Error('expected a durable tool result before compaction')
      const precedingStepEnd = events.find(event =>
        event.type === 'step/end'
        && event.data.step === precedingResult.data.step
        && event.seq > precedingResult.seq,
      )
      const nextStepStart = events.find(event =>
        event.type === 'step/start'
        && event.data.step === precedingResult.data.step + 1
        && event.seq > compactStart!.seq,
      )
      expect(precedingResult.seq).toBeLessThan(compactStart!.seq)
      expect(precedingStepEnd!.seq).toBeLessThan(compactStart!.seq)
      expect(compactStart!.seq).toBeLessThan(nextStepStart!.seq)
    } finally {
      await ctx.fiber.dispose()
    }
  })

  it('the head checkpoint the loop lands is a balanced cut on both sides', async () => {
    const { ctx } = await harness(8)
    try {
      const agent = await ctx.agentLoop.create(SessionId('repro'), { provider: 'mock', model: 'mock' })
      agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do a long multi-step task' }], source: { kind: 'user' } }))
      await waitForIdle(ctx, agent)

      const events = agent.session.snapshotEvents()
      // A compaction ran: at least one checkpoint landed on the surface.
      const checkpoints = events.filter(
        (e): e is SurfaceEvent =>
          e.type === 'user/message'
          && typeof (e as SurfaceEvent).surfaceOp === 'object',
      )
      expect(checkpoints.length).toBeGreaterThan(0)

      // High log position does not make a text-only checkpoint mid-step; both
      // its start and end cuts are balanced in surface order.
      const nodes = agent.session.surface.nodes
      for (const cp of checkpoints) {
        const index = nodes.indexOf(cp.seq)
        if (index === -1) continue // shadowed by a later checkpoint — no longer an edge.
        expect(toolPairingBalancedBefore(agent.session, cp.seq),
          `checkpoint seq ${cp.seq} must be a balanced region START`).toBe(true)
        expect(toolPairingBalancedAfter(agent.session, cp.seq),
          `checkpoint seq ${cp.seq} must be a balanced region END`).toBe(true)
      }
    } finally {
      await ctx.fiber.dispose()
    }
  })
})

describe('token pressure after loop-admitted system prompts', () => {
  it.each([false, true])('counts initial and replaced prompts once with retry=%s', async (retry) => {
    const ctx = new Context()
    const requests: GenerateOptions[] = []
    const usage = { inputTokens: 1000, cacheReadTokens: 100, outputTokens: 10 }
    const adapter = new class extends StepwiseToolAdapter {
      override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
        requests.push(options)
        yield { type: 'block-start', index: 0, blockType: 'text' }
        yield { type: 'block-end', index: 0, block: { type: 'text', text: 'answer' } }
        yield { type: 'usage', usage }
        yield retry && requests.length === 1
          ? { type: 'finish', reason: { kind: 'error', failure: { code: 'SERVER', message: 'retry me' } } }
          : { type: 'finish', reason: { kind: 'stop' } }
      }
    }(0)
    try {
      await mountAgentLoopTestDependencies(ctx)
      await ctx.plugin(AgentLoop, { agents: [] })
      await ctx.plugin(TokenMeter)
      ctx.llm.registerAdapter(['mock'], adapter)
      let prompt = 'initial guidance '.repeat(8)
      ctx.systemPrompt.section({ name: 'meter-test', order: 0, complete: true, text: () => prompt })
      ctx.on('agent/request', async (_payload, next) => ({ ...await next(), temperature: 0.5 }))
      ctx.on('agent/request-error', async ({ agent, turn, step }, next) => {
        const action = await next()
        if (action !== undefined) return action
        const node = agent.session.surface.nodes[0]!
        agent.session.append('system/message', {
          turn,
          step,
          message: createSystemMessage('retry guidance', '@deepseek-ai/dsh-system-prompt'),
        }, { surfaceOp: { op: 'replace', startSeq: node, endSeq: node }, sourceEventSeqs: [node] })
        return { kind: 'retry' }
      })
      const agent = await ctx.agentLoop.create(SessionId('prompt-pressure'), { provider: 'mock', model: 'mock' })
      // Eager replay must observe the same anchor as a fresh reader of the finished log.
      ctx.tokenMeter.measure(agent.session)
      for (const nextPrompt of [prompt, 'expanded guidance '.repeat(20), 'short', '']) {
        prompt = nextPrompt
        agent.followup(createUserMessage({ content: [{ type: 'text', text: 'question' }], source: { kind: 'user' } }))
        await agent.whenIdle()
        expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
          type: 'turn/end', data: { reason: { kind: 'completed' } },
        })
        const measured = ctx.tokenMeter.measure(agent.session)
        expect(measured.baseline).toEqual({ kind: 'usage', tokens: 1110, usage })
        expect(measured.surfaceDeltaTokens).toBe(0)
        expect(measured.totalTokens).toBe(1110)
        const replay = Session.create(SessionId('prompt-pressure-replay'), agent.session.snapshotEvents())
        expect(ctx.tokenMeter.measure(replay)).toMatchObject({
          baseline: measured.baseline, surfaceDeltaTokens: 0, totalTokens: 1110, nodes: measured.nodes,
        })
      }
      const events = agent.session.snapshotEvents()
      const prompts = events.filter(event => event.type === 'system/message')
      expect(prompts[0]?.surfaceOp).toBe('append')
      expect(prompts.slice(1).every(event => typeof event.surfaceOp === 'object')).toBe(true)
      for (const event of prompts) {
        expect(events.find(start => start.type === 'step/start'
          && start.data.turn === event.data.turn && start.data.step === event.data.step)?.seq)
          .toBeLessThan(event.seq)
      }
      expect(requests).toHaveLength(retry ? 5 : 4)
      expect(requests.every(request => request.temperature === 0.5)).toBe(true)
      expect(events.filter(event => event.type === 'assistant/attempt')).toHaveLength(retry ? 1 : 0)
      expect(events.filter(event => event.type === 'step/start')).toHaveLength(4)
      expect(requests[0]?.messages[0]?.content).toEqual([{ type: 'text', text: 'initial guidance '.repeat(8) }])
      if (retry) expect(requests[1]?.messages[0]?.content).toEqual(requests[0]?.messages[0]?.content)
      expect(requests.at(-1)?.messages.some(message => message.role === 'system')).toBe(false)
    } finally {
      await ctx.fiber.dispose()
    }
  })
})

describe('context-overflow recovery across the real loop and compaction-basic', () => {
  it.each(['thrown', 'in-band'] as const)(
    'force-compacts a %s overflow within the retried step',
    async (delivery) => {
      const ctx = new Context()
      const adapter = new OverflowRecoveryAdapter(delivery)
      await mountAgentLoopTestDependencies(ctx)
      await mountInvariants(ctx)
      await ctx.plugin(AgentLoop, { agents: [] })
      await ctx.plugin(TokenMeter)
      ctx.llm.registerAdapter(['mock'], adapter)
      ctx.on('agent/request', async (_payload, next) => ({
        ...await next(), provider: 'mock', model: 'mock',
      }))
      await ctx.plugin(BasicCompactionEngine, {
        thresholdRatio: 1,
        retainTokens: 100,
        maxTokens: 64,
        compactionRetries: 0,
        maxOverflowRetries: 1,
      })

      try {
        const { agent } = await ctx.agentLoop.createAgent(ctx, {
          sessionId: SessionId(`overflow-${delivery}`),
          seed: overflowHistorySeed(),
          agentOptions: {
            provider: 'unconfigured-agent-fallback',
            model: 'unconfigured-agent-fallback',
          },
        })

        agent.followup(createUserMessage({ content: [{ type: 'text', text: 'continue from history' }], source: { kind: 'user' } }))
        await agent.whenIdle()

        expect(adapter.conversationRequests).toHaveLength(2)
        expect(adapter.summaryRequests).toHaveLength(1)
        const instruction = adapter.summaryRequests[0]!.messages.at(-1)?.content
          .map(block => (block.type === 'text' ? block.text : ''))
          .join('') ?? ''
        expect(instruction).toContain('Write concise English engineering prose.')
        expect(instruction).toContain('numeric values, function signatures, and syntax fragments.')
        expect(JSON.stringify(adapter.conversationRequests[0]!.messages)).toContain('OLD HISTORY SENTINEL')
        const retry = JSON.stringify(adapter.conversationRequests[1]!.messages)
        expect(retry).toContain('RECOVERY CHECKPOINT')
        expect(retry).not.toContain('OLD HISTORY SENTINEL')

        const events = agent.session.snapshotEvents()
        const stepStart = events.find(event =>
          event.type === 'step/start' && event.data.turn === 3 && event.data.step === 1,
        )!
        const stepEnd = events.find(event =>
          event.type === 'step/end' && event.data.turn === 3 && event.data.step === 1,
        )!
        const compaction = events.filter(event =>
          event.type === 'compaction/start'
          || event.type === 'compaction/summary'
          || event.type === 'compaction/end',
        )
        expect(compaction.map(event => event.type)).toEqual([
          'compaction/start',
          'compaction/summary',
          'compaction/end',
        ])
        expect(compaction.every(event =>
          event.seq > stepStart.seq && event.seq < stepEnd.seq,
        )).toBe(true)
        expect(events.filter(event => event.type === 'turn/start').slice(-1).map(event => event.data.turn))
          .toEqual([3])
        expect(events.filter(event => event.type === 'step/start' && event.data.turn === 3))
          .toHaveLength(1)
        expect(events.at(-1)).toMatchObject({
          type: 'turn/end',
          data: { reason: { kind: 'completed' } },
        })
      } finally {
        await ctx.fiber.dispose()
      }
    },
  )

  it('keeps context-overflow and transient retry budgets independent in one sequence', async () => {
    const ctx = new Context()
    const adapter = new OverflowRecoveryAdapter('thrown', true)
    await mountAgentLoopTestDependencies(ctx)
    await mountInvariants(ctx)
    await ctx.plugin(LlmRetry)
    await ctx.plugin(AgentLoop, { agents: [] })
    await ctx.plugin(TokenMeter)
    ctx.llm.registerAdapter(['mock'], adapter)
    await ctx.plugin(BasicCompactionEngine, {
      thresholdRatio: 1,
      retainTokens: 100,
      maxTokens: 64,
      compactionRetries: 0,
      maxOverflowRetries: 1,
    })

    try {
      const { agent } = await ctx.agentLoop.createAgent(ctx, {
        sessionId: SessionId('alternating-recovery'),
        seed: overflowHistorySeed(),
        agentOptions: { provider: 'mock', model: 'mock' },
      })
      agent.followup(createUserMessage({ content: [{ type: 'text', text: 'continue from history' }], source: { kind: 'user' } }))
      await agent.whenIdle()

      expect(adapter.conversationRequests).toHaveLength(3)
      expect(adapter.summaryRequests).toHaveLength(1)
      expect(agent.session.snapshotEvents().filter(event => event.type === 'llm/retry').map(event => event.data))
        .toEqual([expect.objectContaining({ turn: 3, step: 1, retry: 1, failure: { message: 'temporary provider outage', code: 'SERVER' } })])
      expect(agent.session.snapshotEvents().filter(event => event.type === 'turn/start').slice(-1).map(event => event.data.turn))
        .toEqual([3])
      expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
        type: 'turn/end',
        data: { reason: { kind: 'completed' } },
      })
    } finally {
      await ctx.fiber.dispose()
    }
  })
})

	import { describe, expect, it } from 'vitest'
	import { Context } from '@deepseek-ai/cordis'
	import { toolPairingBalancedAfter, toolPairingBalancedBefore } from '@deepseek-ai/dsh-compaction'
	import { createUserMessage, createSystemMessage, CONTEXT_WINDOW_EXCEEDED_CODE, LlmError, resolveRetryPolicy , createMessage } from '@deepseek-ai/dsh-llm'
	import type { ContentBlock, GenerateOptions, LlmResolvedModelInfo, ResolvedRetryPolicy, StreamChunk } from '@deepseek-ai/dsh-llm'
	import { ToolCallId, LlmAdapter } from '@deepseek-ai/dsh-llm'
	import { defineContentToolFixture } from '@deepseek-ai/dsh-tools'
	import type { Agent } from '@deepseek-ai/dsh-agent'
	import AgentLoop from '@deepseek-ai/dsh-agent-loop'
	import { mountAgentLoopTestDependencies } from '@deepseek-ai/dsh-agent-loop-testkit'
	import InvariantRegistry from '@deepseek-ai/dsh-invariants'
	import * as SessionInvariant from '@deepseek-ai/dsh-session/invariant'
	import * as AgentInvariant from '@deepseek-ai/dsh-agent/invariant'
	import * as AgentLoopInvariant from '@deepseek-ai/dsh-agent-loop/invariant'
	import { BasicCompactionEngine } from '@deepseek-ai/dsh-compaction-basic'
	import TokenMeter from '@deepseek-ai/dsh-token-meter'
	import * as LlmRetry from '@deepseek-ai/dsh-llm-retry'
	import { Session, SessionId, type SessionEvent, type SurfaceEvent } from '@deepseek-ai/dsh-session'

	/**
	* CBR-001 regression through the real loop. A replacement checkpoint has a high
	* log seq at the surface head and carries no tool pair, so both adjacent cuts
	* must be safe and re-compacting that checkpoint alone must succeed. This pins
	* surface-position semantics rather than raw-log scanning.
	*/

	class ReproCompactionEngine extends BasicCompactionEngine {
	override async summarize(): Promise<{ summary: ContentBlock[]; provider: string; model: string }> {
	return {
	summary: [{ type: 'text', text: 'CHECKPOINT SUMMARY' }],
	provider: 'mock',
	model: 'stub',
	}
	}
	}

	/** Each call emits one tool-call until exhausted, then a final text answer. */
	class StepwiseToolAdapter extends LlmAdapter {
	calls = 0
	constructor(private toolSteps: number) {
	super()
	}

	override resolveModel(provider: string, model: string): Promise<LlmResolvedModelInfo> {
	return Promise.resolve({
	provider,
	id: model,
	name: model,
	context: { contextWindow: 400 },
	})
	}

	async * stream(_options: GenerateOptions): AsyncIterable<StreamChunk> {
	const n = this.calls
	this.calls += 1
	if (n < this.toolSteps) {
	const id = ToolCallId(`c${n}`)
	const args = `{"i":${n}}`
	yield { type: 'block-start', index: 0, blockType: 'text' }
	yield { type: 'block-end', index: 0, block: { type: 'text', text: `step ${n}` } }
	yield { type: 'block-start', index: 1, blockType: 'tool-call' }
	yield { type: 'block-end', index: 1, block: { type: 'tool-call', id, name: 'work', arguments: args } }
	yield { type: 'finish', reason: { kind: 'tool-calls' } }
	return
	}
	yield { type: 'block-start', index: 0, blockType: 'text' }
	yield { type: 'block-end', index: 0, block: { type: 'text', text: 'all done' } }
	yield { type: 'finish', reason: { kind: 'stop' } }
	}
	}

	/** First conversation request overflows, then the rebuilt retry succeeds. */
	class OverflowRecoveryAdapter extends LlmAdapter {
	readonly conversationRequests: GenerateOptions[] = []
	readonly summaryRequests: GenerateOptions[] = []
	private readonly retryPolicy = resolveRetryPolicy({
	mode: 'normal',
	maxRetries: 1,
	backoff: { initialDelayMs: 1, maxDelayMs: 1, jitterRatio: 0 },
	}, 'compaction test provider retryPolicy')

	constructor(
	private readonly delivery: 'thrown' \| 'in-band',
	private readonly transientAfterOverflow = false,
	) {
	super()
	}

	override resolveModel(provider: string, model: string): Promise<LlmResolvedModelInfo> {
	return Promise.resolve({
	provider,
	id: model,
	name: model,
	context: { contextWindow: 128 },
	})
	}

	override providerRetryPolicy(_provider: string): ResolvedRetryPolicy {
	return this.retryPolicy
	}

	override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
	// The cache-reusing summarizer replays the conversation prefix and marks
	// its call only by the compaction instruction in the trailing user message.
	const trailing = options.messages.at(-1)?.content
	.map(block => (block.type === 'text' ? block.text : ''))
	.join('') ?? ''
	if (trailing.includes('acting as a compaction engine')) {
	this.summaryRequests.push(options)
	yield { type: 'block-start', index: 0, blockType: 'text' }
	yield { type: 'block-end', index: 0, block: { type: 'text', text: 'RECOVERY CHECKPOINT' } }
	yield { type: 'finish', reason: { kind: 'stop' } }
	return
	}

	this.conversationRequests.push(options)
	if (this.conversationRequests.length === 1) {
	if (this.delivery === 'thrown') {
	throw new LlmError('request too large for model context', CONTEXT_WINDOW_EXCEEDED_CODE)
	}
	yield {
	type: 'finish',
	reason: {
	kind: 'error',
	failure: {
	message: 'request too large for model context',
	code: CONTEXT_WINDOW_EXCEEDED_CODE,
	},
	},
	}
	return
	}
	if (this.transientAfterOverflow && this.conversationRequests.length === 2) {
	throw new LlmError('temporary provider outage', 'SERVER')
	}
	yield { type: 'block-start', index: 0, blockType: 'text' }
	yield { type: 'block-end', index: 0, block: { type: 'text', text: 'recovered' } }
	yield { type: 'finish', reason: { kind: 'stop' } }
	}
	}

	async function mountInvariants(ctx: Context): Promise<void> {
	await ctx.plugin(InvariantRegistry)
	await ctx.plugin(SessionInvariant)
	await ctx.plugin(AgentInvariant)
	await ctx.plugin(AgentLoopInvariant)
	}

	async function harness(toolSteps: number): Promise<{ ctx: Context; compact: ReproCompactionEngine }> {
	const ctx = new Context()
	await mountAgentLoopTestDependencies(ctx)
	await mountInvariants(ctx)
	await ctx.plugin(AgentLoop, { agents: [] })
	await ctx.plugin(TokenMeter)
	ctx.llm.registerAdapter(['mock'], new StepwiseToolAdapter(toolSteps))
	ctx.tools.register(defineContentToolFixture({
	name: 'work',
	description: 'does work',
	parameters: { i: { type: 'number' } },
	async execute() {
	return [{ type: 'text', text: 'work result' }]
	},
	}))
	// Small window so several tool steps cross the threshold and compaction
	// fires within the runaway turn after enough history can shrink.
	const compact = new ReproCompactionEngine(ctx, {
	auto: true,
	thresholdRatio: 0.5,
	retainTokens: 50,
	maxTokens: 8192,
	compactionRetries: 1,
	})
	return { ctx, compact }
	}

	function waitForIdle(ctx: Context, agent: Agent): Promise<void> {
	return new Promise((resolve) => {
	const dispose = ctx.on('agent/status', ({ agent: subject, status }) => {
	if (subject === agent && status === 'idle') {
	dispose()
	resolve()
	}
	})
	})
	}

	function overflowHistorySeed(): readonly SessionEvent[] {
	const session = Session.create(SessionId('overflow-history-seed'))
	for (let turn = 1; turn <= 2; turn += 1) {
	const sentinel = turn === 1 ? 'OLD HISTORY SENTINEL' : 'RECENT HISTORY'
	session.append('turn/start', {
	turn,
	})
	session.append('user/message', createUserMessage({
	content: [{ type: 'text', text: `${sentinel} ${'old context '.repeat(200)}` }],
	source: { kind: 'user' },
	}), { surfaceOp: 'append' })
	session.append('step/start', { turn, step: 1 })
	session.append('assistant/message', {
	stream: [],
	turn,
	step: 1,
	message: createMessage({
	role: 'assistant',
	content: [{ type: 'text', text: `historical response ${turn} ${'detail '.repeat(200)}` }],
	source: {
	kind: 'model',
	...{ provider: 'mock', model: 'mock' },
	},
	}),
	}, { surfaceOp: 'append' })
	session.append('step/end', { turn, step: 1 })
	session.append('turn/end', { turn, reason: { kind: 'completed' } })
	}
	return session.snapshotEvents()
	}

	describe('CBR-001: a real-loop checkpoint is a valid boundary on both sides', () => {
	it('uses the model actually routed by agent/request for post-step pressure', async () => {
	const { ctx } = await harness(8)
	ctx.on('agent/request', async (_payload, next) => ({
	...await next(), provider: 'mock', model: 'mock',
	}))
	try {
	const agent = await ctx.agentLoop.create(SessionId('routed-pressure'), {
	provider: 'unconfigured-agent-fallback',
	model: 'unconfigured-agent-fallback',
	})
	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do a routed multi-step task' }], source: { kind: 'user' } }))
	await waitForIdle(ctx, agent)

	expect(agent.session.requestHeader()?.config.model).toBe('mock')
	expect(agent.session.snapshotEvents().some(event => event.type === 'compaction/summary')).toBe(true)
	expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
	type: 'turn/end',
	data: { reason: { kind: 'completed' } },
	})
	} finally {
	await ctx.fiber.dispose()
	}
	})

	it('runs automatic pressure between the completed tool step and the next step', async () => {
	const { ctx } = await harness(8)
	try {
	const agent = await ctx.agentLoop.create(SessionId('post-step-order'), { provider: 'mock', model: 'mock' })
	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do tool work' }], source: { kind: 'user' } }))
	await waitForIdle(ctx, agent)

	const events = agent.session.snapshotEvents()
	const compactStart = events.find(event => event.type === 'compaction/start')
	expect(compactStart).toBeDefined()
	const precedingResult = events.findLast(event =>
	event.type === 'tool/result' && event.seq < compactStart!.seq,
	)
	if (precedingResult?.type !== 'tool/result') throw new Error('expected a durable tool result before compaction')
	const precedingStepEnd = events.find(event =>
	event.type === 'step/end'
	&& event.data.step === precedingResult.data.step
	&& event.seq > precedingResult.seq,
	)
	const nextStepStart = events.find(event =>
	event.type === 'step/start'
	&& event.data.step === precedingResult.data.step + 1
	&& event.seq > compactStart!.seq,
	)
	expect(precedingResult.seq).toBeLessThan(compactStart!.seq)
	expect(precedingStepEnd!.seq).toBeLessThan(compactStart!.seq)
	expect(compactStart!.seq).toBeLessThan(nextStepStart!.seq)
	} finally {
	await ctx.fiber.dispose()
	}
	})

	it('the head checkpoint the loop lands is a balanced cut on both sides', async () => {
	const { ctx } = await harness(8)
	try {
	const agent = await ctx.agentLoop.create(SessionId('repro'), { provider: 'mock', model: 'mock' })
	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'do a long multi-step task' }], source: { kind: 'user' } }))
	await waitForIdle(ctx, agent)

	const events = agent.session.snapshotEvents()
	// A compaction ran: at least one checkpoint landed on the surface.
	const checkpoints = events.filter(
	(e): e is SurfaceEvent =>
	e.type === 'user/message'
	&& typeof (e as SurfaceEvent).surfaceOp === 'object',
	)
	expect(checkpoints.length).toBeGreaterThan(0)

	// High log position does not make a text-only checkpoint mid-step; both
	// its start and end cuts are balanced in surface order.
	const nodes = agent.session.surface.nodes
	for (const cp of checkpoints) {
	const index = nodes.indexOf(cp.seq)
	if (index === -1) continue // shadowed by a later checkpoint — no longer an edge.
	expect(toolPairingBalancedBefore(agent.session, cp.seq),
	`checkpoint seq ${cp.seq} must be a balanced region START`).toBe(true)
	expect(toolPairingBalancedAfter(agent.session, cp.seq),
	`checkpoint seq ${cp.seq} must be a balanced region END`).toBe(true)
	}
	} finally {
	await ctx.fiber.dispose()
	}
	})
	})

	describe('token pressure after loop-admitted system prompts', () => {
	it.each([false, true])('counts initial and replaced prompts once with retry=%s', async (retry) => {
	const ctx = new Context()
	const requests: GenerateOptions[] = []
	const usage = { inputTokens: 1000, cacheReadTokens: 100, outputTokens: 10 }
	const adapter = new class extends StepwiseToolAdapter {
	override async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
	requests.push(options)
	yield { type: 'block-start', index: 0, blockType: 'text' }
	yield { type: 'block-end', index: 0, block: { type: 'text', text: 'answer' } }
	yield { type: 'usage', usage }
	yield retry && requests.length === 1
	? { type: 'finish', reason: { kind: 'error', failure: { code: 'SERVER', message: 'retry me' } } }
	: { type: 'finish', reason: { kind: 'stop' } }
	}
	}(0)
	try {
	await mountAgentLoopTestDependencies(ctx)
	await ctx.plugin(AgentLoop, { agents: [] })
	await ctx.plugin(TokenMeter)
	ctx.llm.registerAdapter(['mock'], adapter)
	let prompt = 'initial guidance '.repeat(8)
	ctx.systemPrompt.section({ name: 'meter-test', order: 0, complete: true, text: () => prompt })
	ctx.on('agent/request', async (_payload, next) => ({ ...await next(), temperature: 0.5 }))
	ctx.on('agent/request-error', async ({ agent, turn, step }, next) => {
	const action = await next()
	if (action !== undefined) return action
	const node = agent.session.surface.nodes[0]!
	agent.session.append('system/message', {
	turn,
	step,
	message: createSystemMessage('retry guidance', '@deepseek-ai/dsh-system-prompt'),
	}, { surfaceOp: { op: 'replace', startSeq: node, endSeq: node }, sourceEventSeqs: [node] })
	return { kind: 'retry' }
	})
	const agent = await ctx.agentLoop.create(SessionId('prompt-pressure'), { provider: 'mock', model: 'mock' })
	// Eager replay must observe the same anchor as a fresh reader of the finished log.
	ctx.tokenMeter.measure(agent.session)
	for (const nextPrompt of [prompt, 'expanded guidance '.repeat(20), 'short', '']) {
	prompt = nextPrompt
	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'question' }], source: { kind: 'user' } }))
	await agent.whenIdle()
	expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
	type: 'turn/end', data: { reason: { kind: 'completed' } },
	})
	const measured = ctx.tokenMeter.measure(agent.session)
	expect(measured.baseline).toEqual({ kind: 'usage', tokens: 1110, usage })
	expect(measured.surfaceDeltaTokens).toBe(0)
	expect(measured.totalTokens).toBe(1110)
	const replay = Session.create(SessionId('prompt-pressure-replay'), agent.session.snapshotEvents())
	expect(ctx.tokenMeter.measure(replay)).toMatchObject({
	baseline: measured.baseline, surfaceDeltaTokens: 0, totalTokens: 1110, nodes: measured.nodes,
	})
	}
	const events = agent.session.snapshotEvents()
	const prompts = events.filter(event => event.type === 'system/message')
	expect(prompts[0]?.surfaceOp).toBe('append')
	expect(prompts.slice(1).every(event => typeof event.surfaceOp === 'object')).toBe(true)
	for (const event of prompts) {
	expect(events.find(start => start.type === 'step/start'
	&& start.data.turn === event.data.turn && start.data.step === event.data.step)?.seq)
	.toBeLessThan(event.seq)
	}
	expect(requests).toHaveLength(retry ? 5 : 4)
	expect(requests.every(request => request.temperature === 0.5)).toBe(true)
	expect(events.filter(event => event.type === 'assistant/attempt')).toHaveLength(retry ? 1 : 0)
	expect(events.filter(event => event.type === 'step/start')).toHaveLength(4)
	expect(requests[0]?.messages[0]?.content).toEqual([{ type: 'text', text: 'initial guidance '.repeat(8) }])
	if (retry) expect(requests[1]?.messages[0]?.content).toEqual(requests[0]?.messages[0]?.content)
	expect(requests.at(-1)?.messages.some(message => message.role === 'system')).toBe(false)
	} finally {
	await ctx.fiber.dispose()
	}
	})
	})

	describe('context-overflow recovery across the real loop and compaction-basic', () => {
	it.each(['thrown', 'in-band'] as const)(
	'force-compacts a %s overflow within the retried step',
	async (delivery) => {
	const ctx = new Context()
	const adapter = new OverflowRecoveryAdapter(delivery)
	await mountAgentLoopTestDependencies(ctx)
	await mountInvariants(ctx)
	await ctx.plugin(AgentLoop, { agents: [] })
	await ctx.plugin(TokenMeter)
	ctx.llm.registerAdapter(['mock'], adapter)
	ctx.on('agent/request', async (_payload, next) => ({
	...await next(), provider: 'mock', model: 'mock',
	}))
	await ctx.plugin(BasicCompactionEngine, {
	thresholdRatio: 1,
	retainTokens: 100,
	maxTokens: 64,
	compactionRetries: 0,
	maxOverflowRetries: 1,
	})

	try {
	const { agent } = await ctx.agentLoop.createAgent(ctx, {
	sessionId: SessionId(`overflow-${delivery}`),
	seed: overflowHistorySeed(),
	agentOptions: {
	provider: 'unconfigured-agent-fallback',
	model: 'unconfigured-agent-fallback',
	},
	})

	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'continue from history' }], source: { kind: 'user' } }))
	await agent.whenIdle()

	expect(adapter.conversationRequests).toHaveLength(2)
	expect(adapter.summaryRequests).toHaveLength(1)
	const instruction = adapter.summaryRequests[0]!.messages.at(-1)?.content
	.map(block => (block.type === 'text' ? block.text : ''))
	.join('') ?? ''
	expect(instruction).toContain('Write concise English engineering prose.')
	expect(instruction).toContain('numeric values, function signatures, and syntax fragments.')
	expect(JSON.stringify(adapter.conversationRequests[0]!.messages)).toContain('OLD HISTORY SENTINEL')
	const retry = JSON.stringify(adapter.conversationRequests[1]!.messages)
	expect(retry).toContain('RECOVERY CHECKPOINT')
	expect(retry).not.toContain('OLD HISTORY SENTINEL')

	const events = agent.session.snapshotEvents()
	const stepStart = events.find(event =>
	event.type === 'step/start' && event.data.turn === 3 && event.data.step === 1,
	)!
	const stepEnd = events.find(event =>
	event.type === 'step/end' && event.data.turn === 3 && event.data.step === 1,
	)!
	const compaction = events.filter(event =>
	event.type === 'compaction/start'
	\|\| event.type === 'compaction/summary'
	\|\| event.type === 'compaction/end',
	)
	expect(compaction.map(event => event.type)).toEqual([
	'compaction/start',
	'compaction/summary',
	'compaction/end',
	])
	expect(compaction.every(event =>
	event.seq > stepStart.seq && event.seq < stepEnd.seq,
	)).toBe(true)
	expect(events.filter(event => event.type === 'turn/start').slice(-1).map(event => event.data.turn))
	.toEqual([3])
	expect(events.filter(event => event.type === 'step/start' && event.data.turn === 3))
	.toHaveLength(1)
	expect(events.at(-1)).toMatchObject({
	type: 'turn/end',
	data: { reason: { kind: 'completed' } },
	})
	} finally {
	await ctx.fiber.dispose()
	}
	},
	)

	it('keeps context-overflow and transient retry budgets independent in one sequence', async () => {
	const ctx = new Context()
	const adapter = new OverflowRecoveryAdapter('thrown', true)
	await mountAgentLoopTestDependencies(ctx)
	await mountInvariants(ctx)
	await ctx.plugin(LlmRetry)
	await ctx.plugin(AgentLoop, { agents: [] })
	await ctx.plugin(TokenMeter)
	ctx.llm.registerAdapter(['mock'], adapter)
	await ctx.plugin(BasicCompactionEngine, {
	thresholdRatio: 1,
	retainTokens: 100,
	maxTokens: 64,
	compactionRetries: 0,
	maxOverflowRetries: 1,
	})

	try {
	const { agent } = await ctx.agentLoop.createAgent(ctx, {
	sessionId: SessionId('alternating-recovery'),
	seed: overflowHistorySeed(),
	agentOptions: { provider: 'mock', model: 'mock' },
	})
	agent.followup(createUserMessage({ content: [{ type: 'text', text: 'continue from history' }], source: { kind: 'user' } }))
	await agent.whenIdle()

	expect(adapter.conversationRequests).toHaveLength(3)
	expect(adapter.summaryRequests).toHaveLength(1)
	expect(agent.session.snapshotEvents().filter(event => event.type === 'llm/retry').map(event => event.data))
	.toEqual([expect.objectContaining({ turn: 3, step: 1, retry: 1, failure: { message: 'temporary provider outage', code: 'SERVER' } })])
	expect(agent.session.snapshotEvents().filter(event => event.type === 'turn/start').slice(-1).map(event => event.data.turn))
	.toEqual([3])
	expect(agent.session.snapshotEvents().at(-1)).toMatchObject({
	type: 'turn/end',
	data: { reason: { kind: 'completed' } },
	})
	} finally {
	await ctx.fiber.dispose()
	}
	})
	})