think: expose additive TurnConfig stopWhen conditions

[whoiskatrin]

Summary

Expose additive AI SDK stopWhen conditions through Think's TurnConfig.

Think already owns the streamText() call and maps maxSteps to:

stopWhen: stepCountIs(maxSteps)

That covers step-count limits, but it leaves no way for Think subclasses to express other AI SDK stop conditions such as:

hasToolCall("finalAnswer")

This PR adds:

beforeTurn() {
  return {
    stopWhen: hasToolCall("finalAnswer")
  };
}

Behavior

Custom stopWhen conditions are additive.

Think now sends both:

• its existing stepCountIs(maxSteps) safety bound
• any custom TurnConfig.stopWhen condition(s)

to the AI SDK, so the loop ends when either matches.

That means callers can stop early after a designated tool call without silently removing Think's existing runaway-loop guardrail.

API

interface TurnConfig {
  maxSteps?: number;
  stopWhen?: StopCondition | StopCondition[];
}

Example:

import { hasToolCall } from "ai";

beforeTurn() {
  return {
    stopWhen: hasToolCall("finalAnswer")
  };
}

StopCondition is also re-exported from @cloudflare/think alongside the other AI SDK lifecycle-facing types.

Notes on extensions

stopWhen is function-valued, so it is supported from a Think subclass's beforeTurn() hook, but not from sandboxed extension beforeTurn hooks over RPC.

The docs call this out explicitly.

Tests

Added regression coverage verifying that:

• a Think turn can return stopWhen: hasToolCall("echo")
• the tool executes
• Think does not start the follow-up continuation model step after that matching tool call

Documentation

Updated:

• packages/think/README.md
• docs/think/lifecycle-hooks.md

to document:

• TurnConfig.stopWhen
• composition with maxSteps
• hasToolCall(...) usage
• subclass-only support for function-valued stop conditions

Validation

Passed:

npm run build --workspace @cloudflare/think
npm run build --workspace agents
npx vitest --run -c packages/think/src/tests/vitest.config.ts packages/think/src/tests/hooks.test.ts

Focused Think hook suite:

66 passed

Also ran:

npm run check

Formatting, exports, and lint passed. Repo-wide typecheck could not complete in this environment because tsgo is unavailable:

/bin/sh: tsgo: command not found

[changeset-bot]

🦋 Changeset detected

Latest commit: fb5745b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/think	Patch

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[devin-ai-integration]

✅ Devin Review: No Issues Found

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