The Claude Code mimic path rewrites tool names in tools[] (and
tool_choice) but left tool_use blocks in messages[] with their
original names. Anthropic validates that every tool referenced by
a tool_use block is declared in tools[], so the mismatch produces:
messages.N.content.M: Input tag 'original_name' not found in tools
(surfaced as HTTP 400 directly, or wrapped as 424 by upstream proxies
such as Bedrock gateways.)
The previous code comment asserted 'this matches Parrot; response-side
bytes.Replace will restore the names'. Parrot's behavior is fine for
Claude Code's own tool set, but breaks once the upstream client sends
additional tools (e.g. web_search) that are not part of Claude Code
and therefore get renamed here.
Fix: apply the same ToolNameRewrite to messages[].content[] blocks
where type == 'tool_use', keeping tools[], tool_choice and messages
self-consistent before the request reaches Anthropic. tool_result
blocks reference tools via tool_use_id, not name, so no change is
needed there.
A new unit test covers the full rewrite flow and guards against
server tools (type != '') being affected.
f97b853460