[pcbeingused333]

Why: The Workers AI streaming instrumentation (accumulateStreamingToolCalls) keyed every tool-call delta by toolCall.index ?? 0. OpenAI-compatible endpoints that omit index and send each parallel call whole in its own chunk therefore ended up as a single call: the first call's id and name, with the arguments of every call concatenated, and the other calls missing from gen_ai.response.tool_calls and gen_ai.output.messages. Same situation #25622 fixed for the OpenAI instrumentation.

Tool calls with a numeric index are grouped by it exactly as before. A delta without a usable index (missing or null) is kept in a separate list, in arrival order, so it can never collide with a real index: a delta whose id is already known continues that call, a new id (or a function name without an id) starts a new call, and anything else, such as an arguments fragment with neither, continues the latest one. Native and indexed streams (including the top-level name/arguments shape) behave as before.

How to review: getUnindexedToolCall and the ToolCallAccumulator split in packages/server-utils/src/ai/workers-ai/streaming.ts; the three new cases in workers-ai-streaming.test.ts (two parallel calls without an index stay separate, argument fragments of one unindexed call are merged, an unindexed call does not merge into an indexed call at index: 0). The first and third fail without the change; the whole test/ai/lib/tracing folder passes.

Unsure about: whether an unindexed delta with neither id nor name should continue the latest call (chosen here, mirrors #25622) or be dropped.

Closes: no linked issue; same class of bug as #25622.

This change was prepared with the assistance of an AI coding agent (Claude).