feat: Anthropic eager input streaming for Code API tools

[danny-avila]

Summary

Adds Anthropic's current per-tool eager_input_streaming: true flag to the final Anthropic tool definition for CodeAPI/event-driven execution tools:

• execute_code
• bash_tool
• run_tools_with_code
• run_tools_with_bash
• read_file

The flag is applied only in the Anthropic adapter after LangChain formats tools for Anthropic, because LangChain's generic tool extras schema does not currently pass this field through. Explicit eager_input_streaming: false is preserved, and non-CodeAPI tools are left unchanged.

Research Notes

Anthropic's current docs describe fine-grained tool input streaming as a per-tool eager_input_streaming setting rather than relying solely on the old beta header. Live testing showed input_json_delta events still occur without the field on the tested model, but the field changed chunk/timing behavior and gave earlier tool-input deltas in samples.

Live Validation

Model: claude-haiku-4-5-20251001

Raw Anthropic stream comparison:

Case	First input delta	Delta count	Result
no eager field	1407ms	225	streamed input_json_delta
old beta header only	874ms	83	streamed input_json_delta
per-tool eager_input_streaming	452ms	50	streamed input_json_delta, earliest in sample

Run/eager event pipeline comparison with mocked host execution:

Case	First ON_TOOL_EXECUTE	First model end	Eager before model end
field stripped	2264ms	2290ms	yes
new field	1868ms	2031ms	yes

Validity check at the streamed-tool seal point:

Case	bash first delta	read_file first delta / bash seal	Eager bash args parseable	Eager args == final args
field stripped	838ms	1049ms	yes	yes
eager_input_streaming: true	764ms	964ms	yes	yes

Tests

• ANTHROPIC_API_KEY=test NODE_OPTIONS='--experimental-vm-modules' npx jest src/llm/anthropic/llm.spec.ts --runInBand -t 'Anthropic (CodeAPI tool|fine-grained tool input streaming)'
• ANTHROPIC_API_KEY=test NODE_OPTIONS='--experimental-vm-modules' npx jest src/__tests__/stream.eagerEventExecution.test.ts --runInBand -t 'CodeAPI|eager|stale|redispatch|changed'
• ANTHROPIC_API_KEY=test npx tsc -p tsconfig.json --noEmit
• npx eslint src/llm/anthropic/index.ts
• npx prettier --check src/llm/anthropic/index.ts src/llm/anthropic/llm.spec.ts
• git diff --check

[danny-avila]

@codex review

[chatgpt-codex-connector]

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[danny-avila]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. What shall we delve into next?

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