* fix(anthropic): stop repeating streamed thinking text in the signature chunk
The Anthropic stream handler emitted, on the signature_delta, a thinking block carrying every thinking delta seen so far plus the signature, after it had already streamed that text as per-delta blocks. Every additive consumer (the Agents SDK, stream_chunk_builder, the Responses bridge) stored the text twice under one signature and replayed the doubled block on the next turn
The signature chunk now carries a signature-only block, matching the Bedrock emitter, so accumulators rebuild the text once and the saved history replays to Anthropic exactly as it was streamed
* test(anthropic): audit the signature-only thinking chunk across wire providers
* test(anthropic): pin the cached replay's thinking shape in the wire audit
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Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
