* fix(router): stop a Responses fallback from replaying a delivered tool call
A tool-only Responses stream carries no output text, so a retriable error or
response.failed after a completed function call was treated as a failure before
output and the fallback replayed the whole request, running the tool twice.
Check for a started tool call before the before-output shortcut so the primary
error surfaces instead. Pre-output fallback and text continuation are unchanged.
* test(router): read the delivered tool call events one at a time
Consume the created and output_item.done events with anext and expect the
primary error on the next read, so the raises block holds a single statement.
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Co-authored-by: Joshua Valluru <326636767+joshua-berri@users.noreply.github.com>