why

• addresses #249

what changed

• Strip Anthropic’s beta-only caller field from tool_use blocks before persisting conversation history so subsequent beta.messages.create calls don’t send invalid keys.
• The _process_provider_response path now model_dump()s each response.content block, removes caller, and falls back gracefully if serialization fails.
• Fix ensures Stagehand agents can complete multi-step Claude sessions without the 400 "messages.*.tool_use.caller: Extra inputs are not permitted" error

test plan

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Summary by cubic

Strip Anthropic’s beta-only caller field from tool_use blocks when saving conversation history, so we don’t resend invalid keys on the next call. Fixes the 400 “messages.*.tool_use.caller: Extra inputs are not permitted” error in multi-step Claude sessions (addresses #249).

• Bug Fixes
  • In _process_provider_response, serialize each content block, remove caller, and handle serialization failures gracefully.
  • Prevent invalid keys in beta.messages.create to keep multi-step sessions running.