#5175 feat: Add convenience method to use StackOne third-party tools

Stackone Integration as Third-Party Tools

This PR adds pydantic_ai.ext.stackone so Pydantic AI agents can use StackOne tools, following the pattern already established for LangChain and ACI.dev in the same pydantic_ai.ext namespace

StackOne is Integration Infrastructure for AI Agents. To use it, install the stackone-ai package, set STACKONE_API_KEY in your environment, and provide at least one connected account ID via STACKONE_ACCOUNT_ID or by passing account_ids= directly.

Usage from Pydantic AI

from pydantic_ai import Agent
from pydantic_ai.ext.stackone import StackOneToolset

toolset = StackOneToolset()

agent = Agent('openai:gpt-5.4', toolsets=[toolset])
                                                                                                                                                       
result = agent.run_sync('List the first 5 workers')
print(result.output)                                                                                                                                   

For large catalogs, mode='search_and_execute' exposes two tools (tool_search and tool_execute) that let the model discover and invoke tools at runtime instead of receiving every tool upfront:

toolset = StackOneToolset(mode='search_and_execute')
agent = Agent('openai:gpt-5.4', toolsets=[toolset])                                                                                                    

StackOneToolset also supports narrowing with tools= or filter_pattern=, and multi-account connections via account_ids=[...]

Checklist

• Any AI generated code has been reviewed line-by-line by the human PR author, who stands by it.
• No breaking changes in accordance with the version policy.
• PR title is fit for the release changelog.
• make docs-serve builds and renders the updated StackOne section correctly.
• PR has been made easy and clean for reviewers to review and open to discussion of any further info needed.

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