The canonical Anthropic stream leaves tool_use input empty on
content_block_start and streams the arguments as input_json_delta.
Anthropic-compatible relays may instead put the complete arguments on
content_block_start and send no delta. The Anthropic-to-Responses stream
converter ignored that input, so function_call_arguments.done carried ""
and the closed item "{}", and clients executed the tool with no arguments.
Keep the inline input as a seed. A real input_json_delta supersedes it, so
canonical streams keep their exact event sequence and two JSON documents are
never concatenated. When no delta arrived by content_block_stop, emit the
seed as a single arguments delta before the done event, which still repeats
exactly what the deltas streamed. Empty, "{}" and null inputs keep the
existing "{}" fallback.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
