feat(harness-deepagents): implement harness adapter for Deep Agents

[mlekhi]

Background

DeepAgents is a TS agent runtime. This is the harness adapter for DeepAgents - @ai-sdk/harness-deepagents. Runs the deepagents package through a Node bridge in the sandbox.

• Built-in tools: read, write, edit, bash, grep, glob, ls, task, write_todos
• Host tools work
• Skills work
• Auth: Anthropic, OpenAI, Gateway
• Multi-turn, attach, resume
• Built-in tool approvals (approve/reject) via DeepAgents interruptOn

Manual Verification

Ran the examples for real (model + sandbox):

• examples/ai-functions/src/harness-agent/deepagents/* — all worked
• Approvals: approve → tool runs; reject → tool doesn't run, returns "Rejected by user."
• TUI + Next apps: all variants worked
• 45 unit tests pass

Checklist

• All commits are signed
• Tests added
• Docs added
• Changeset added
• Self-reviewed

[felixarntz]

@mlekhi this works great based on initial testing! the main thing to look into further is proper skills setup, and then some minor fixes around tools. also worth checking whether we can support tool approvals at least for custom tools (like e.g. for Codex).

[felixarntz]

what are the @langchain/anthropic and @langchain/openai dependencies used for?

[mlekhi]

these are the langchain provider packages, createDeepAgent loads them based on the model id. theyre not bundled by deepagents or langchain so without them it just errors at runtime. anthropic is the default, openai only kicks in for openai models. we can drop the openai one if we wanna stay anthropic-only for now.