[Bug] Empty tool_calls arrays split continuous reasoning into separate parts #47875

Description

OpenCode's pinned @ai-sdk/[email protected] closes active reasoning whenever a streamed delta contains tool_calls, even when the array is empty. Consecutive reasoning deltas with tool_calls: [] therefore produce separate persisted reasoning parts instead of one continuous part.

This is the SDK bug tracked in vercel/ai#20203, fixed by vercel/ai#20253 and published in compatible 3.0.44. OpenCode's pinned version still needs the fix. A narrow backport would avoid a major SDK migration.

Related: #40865 describes fragmented Thought blocks, but also content-field behavior outside this report's scope. This report only concerns consecutive reasoning_content deltas with empty tool-call arrays, not merging across real text or tool boundaries.

Plugins

None required; reproduced with local SSE fixtures through the SDK and real session processor.

OpenCode version

dev at ecbc6ccac85b3e8087b6445e584318419b9e2b34; [email protected], @ai-sdk/[email protected], Bun 1.3.14.

Steps to reproduce

1. Configure an OpenAI-compatible test endpoint to return this chat-completion SSE response:

data: {"id":"repro","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"reasoning_content":"r1","tool_calls":[]},"finish_reason":null}]}

data: {"id":"repro","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"reasoning_content":"r2","tool_calls":[]},"finish_reason":null}]}

data: {"id":"repro","object":"chat.completion.chunk","choices":[{"index":0,"delta":{"content":"done"},"finish_reason":null}]}

data: {"id":"repro","object":"chat.completion.chunk","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

data: [DONE]

2. Send a prompt and inspect the assistant's persisted reasoning parts.

Expected: one completed reasoning part, r1r2, followed by text done.

Actual: two completed reasoning parts, r1 and r2; text done remains intact. Omitting tool_calls produces the expected single part.

Screenshot and/or share link

Not applicable; reproduced with headless SDK/session tests, not a live provider account.

Operating System

Linux.

Terminal

Not applicable to the headless reproduction.