fix: preserve callProviderMetadata, providerExecuted, and title on tool parts

[threepointone]

Fixes #1009

Problem

When using Gemini with client-side tools (e.g. addToolOutput), the continuation call after tool output fails with:

Function call is missing a thought_signature in functionCall parts. This is required for tools to work correctly, and missing thought_signature may lead to degraded model performance.

This affects agents SDK v0.5.1+ / @cloudflare/ai-chat v0.1.3+ with the Gemini API. Reproduction: https://github.com/Suman085/agents-issue-reproduction

Root Cause

applyChunkToParts in message-builder.ts — the server-side message builder used by AIChatAgent — was silently dropping providerMetadata from tool-input stream chunks instead of storing it as callProviderMetadata on the resulting tool UIMessage parts.

The AI SDK's own client-side updateToolPart correctly does this mapping:

// AI SDK client-side (correct)
if (anyOptions.providerMetadata != null) {
  part.callProviderMetadata = anyOptions.providerMetadata;
}

But our server-side applyChunkToParts was only storing state and input:

// Our code (before fix — missing callProviderMetadata)
parts.push({
  type: `tool-${chunk.toolName}`,
  toolCallId: chunk.toolCallId,
  toolName: chunk.toolName,
  state: "input-available",
  input: chunk.input
});

Later, when convertToModelMessages reads the persisted messages for the continuation call, it looks for callProviderMetadata and passes it as providerOptions to the model. Since it was never stored, Gemini doesn't receive its thought_signature back and throws the error.

Two additional fields were also missing: providerExecuted (used by convertToModelMessages for provider-executed tools like Gemini code execution) and title (tool display name).

Changes

packages/ai-chat/src/message-builder.ts

• tool-input-start: Store callProviderMetadata, providerExecuted, and title on new tool parts
• tool-input-available: Store all three fields on both create and update paths
• tool-input-error: Store callProviderMetadata and providerExecuted on both create and update paths
• Added providerExecuted to StreamChunkData type explicitly (was previously only accessible via the [key: string]: unknown index signature)

packages/ai-chat/src/react.tsx

• Fixed stale comment that described tool-input-start and tool-input-delta as "unrecognized types" — they are handled by applyChunkToParts

packages/ai-chat/src/tests/message-builder.test.ts

• Added 13 regression tests covering all create/update paths for the three fields
• Tests use Gemini-style google.thoughtSignature metadata to match the real-world failure case

Notes for reviewers

1. Why only tool-input- handlers?* The AI SDK's stream only includes providerMetadata on tool-input-start, tool-input-available, and tool-input-error events. The tool-output-available and tool-output-error events do not carry providerMetadata, so those handlers don't need changes.

2. Sanitization is safe. _sanitizeMessageForPersistence only strips openai-keyed metadata from callProviderMetadata. Google/Gemini metadata (keyed under google) passes through untouched.

3. _applyToolResult is safe. It uses { ...part, state: "output-available", output } spread, so callProviderMetadata, providerExecuted, and title from the original tool part are preserved through the update.

4. All consumers benefit. Server-side streaming (_streamSSEReply), client-side react (react.tsx), and orphaned stream persistence (_persistOrphanedStream) all go through applyChunkToParts, so the fix covers all codepaths.

5. This is a field-by-field parity fix with the AI SDK's updateToolPart. I audited every field the AI SDK stores and confirmed no other fields are missing after this change.

Testing

• 226 tests pass (13 new), 2 pre-existing MCP timeout flakes unrelated to this change
• Build clean
• oxfmt clean

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Latest commit: e7dde8d

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

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Name	Type
@cloudflare/ai-chat	Patch

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