Claude-Code-compatible providers force the executor-level `stream` flag on
via `upstreamStream = stream || isClaudeCodeCompatible`
(open-sse/handlers/chatCore.ts), but the outgoing body keeps the caller's
original `stream: false`. The shared `stream && targetFormat === "openai"`
branch in DefaultExecutor.transformRequest then injected
`stream_options: { include_usage: true }` onto a body that still said
`stream: false`, and qwen upstream rejected the request with
`400 "'stream_options' only set this when you set stream: true"`. The same
rejection surfaced when the body carried `thinking` / `enable_thinking`.
The qwen branch now skips the injection (and strips any client-sent
`stream_options`) when the body explicitly says `stream: false` or
requests thinking, leaving regular qwen streaming requests with the
include_usage injection intact. Other providers are unaffected.
Adds a TDD regression with 4 cases covering both opt-out paths and the
normal-streaming positive control.
Inspired-by: https://github.com/decolua/9router/pull/663
Co-authored-by: anuragg-saxenaa <anuragg.saxenaa@gmail.com>
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