fix: three tool calling bugs causing multi-turn agentic loops to fail

[mchenco]

Summary

Fixes three bugs in workers-ai-provider that collectively caused multi-turn tool calling to fail for new models (@cf/moonshotai/kimi-k2.5, @cf/meta/llama-4-scout-17b-16e-instruct, @cf/zai-org/glm-4.7-flash).

Fixes

1. Tool result output not unwrapped (primary cause of broken agentic loops)

convert-to-workersai-chat-messages.ts was calling JSON.stringify(toolResponse.output) on the full LanguageModelV3ToolResultOutput wrapper ({ type: 'text', value: '...' }), sending the wrapper object as the tool message content instead of just the value. Models received garbled tool results and stopped after the first tool call instead of continuing the loop.

Fix: exhaustive switch over all 7 LanguageModelV3ToolResultOutput variants:

switch (output.type) {
  case "text":
  case "error-text":
    content = output.value;
    break;
  case "json":
  case "error-json":
    content = JSON.stringify(output.value);
    break;
  case "execution-denied":
    content = output.reason
      ? `Tool execution denied: ${output.reason}`
      : "Tool execution was denied.";
    break;
  case "content":
    content = output.value
      .filter((p) => p.type === "text")
      .map((p) => p.text)
      .join("\n");
    break;
  default:
    content = "";
    break;
}

2. toolChoice: "required" mapped to "any" instead of "required"

All models returned 8001: Invalid input for tool_choice: "any". Anyone using toolChoice: "required" or toolChoice: { type: "tool", toolName: "..." } got a hard error.

// Before
case "required": return { tool_choice: "any", tools: mappedTools };
case "tool":     return { tool_choice: "any", tools: filteredTools };

// After
case "required": return { tool_choice: "required", tools: mappedTools };
case "tool":     return { tool_choice: "required", tools: filteredTools };

3. description: false and parameters: false in tool definitions

&& short-circuit evaluated to false (not undefined) for non-function tool types, which would cause 8001: Invalid input if the ai-sdk ever sends a non-function tool type.

// Before
description: tool.type === "function" && tool.description,

// After
description: tool.type === "function" ? tool.description : undefined,

Testing

Unit tests

222 unit tests passing, including new tests covering:

• All 7 LanguageModelV3ToolResultOutput variants (text, json, error-text, error-json, execution-denied, content, unknown)
• toolChoice: "required" mapping
• Tool definition field correctness

E2E tests

E2E tests against real models via both the Workers AI binding and REST API, including two new test scenarios:

• Multi-step agentic loop (T-MS): Model must make 2+ sequential tool calls, correctly read each result, and produce a final text answer. Directly exercises the tool result unwrapping fix.
• toolChoice: "required" (T-Rq): Validates the tool_choice mapping fix — verifies no API error and at least one tool call is made.

Binding E2E results:

Model	Chat	Strm	Turn	Tool	T-RT	T-MS	T-Rq	JSON
Llama 4 Scout 17B	✅	✅	✅	✅	✅	✅	✅	✅
Llama 3.3 70B	✅	✅	✅	✅	~	✅	✅	✅
GPT-OSS 120B	✅	✅	✅	✅	✅	✅	✅	✅
QwQ 32B (reasoning)	✅	✅	✅	✅	✅	✅	❌	✅
Llama 3.1 8B Fast	✅	✅	✅	✅	~	~	✅	✅
GPT-OSS 20B	✅	✅	✅	✅	✅	✅	✅	✅
Qwen3 30B	✅	✅	✅	✅	✅	✅	✅	✅
Kimi K2.5	✅	✅	✅	✅	✅	✅	✅	✅

T-MS = multi-step agentic loop, T-Rq = toolChoice required, ~ = partial (model behavior)

QwQ 32B's T-Rq failure is a server-side model limitation, not a provider bug.

[changeset-bot]

🦋 Changeset detected

Latest commit: cff5c89

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

This PR includes changesets to release 1 package

Name	Type
workers-ai-provider	Patch

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commit: cff5c89

[threepointone]

added some more checks and updated e2e tests, looking good to me now