feat(python): plumb AbortSignal through ToolInvocation for handler cancellation

[gimenete]

Summary

Port of the Node.js AbortSignal implementation (#1433) to the Python SDK.

Adds cooperative cancellation support so tool handlers can detect and respond to session.abort() calls.

Changes

• AbortSignal class with is_aborted property and await signal.wait() coroutine
• AbortController class that creates and manages an AbortSignal
• ToolInvocation.signal field — receives the session's current AbortSignal
• CopilotSession.abort() triggers all in-flight handlers via the signal, then resets the controller for future tool calls
• AbortSignal exported from the top-level copilot package

Usage

from copilot import define_tool, ToolInvocation

@define_tool(description="Fetch remote data")
async def fetch_data(params: Params, inv: ToolInvocation) -> str:
    if inv.signal.is_aborted:
        return "cancelled"
    # Pass signal to cooperative async operations
    async with aiohttp.ClientSession() as s:
        # Poll for abort
        while not inv.signal.is_aborted:
            ...

Backwards compatible

Handlers that don't consume the signal continue to work unchanged.

Closes #1433

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds cooperative cancellation support for tool handlers by introducing an abort signal propagated from CopilotSession.abort() into each ToolInvocation.

Changes:

• Introduces AbortSignal/AbortController and adds ToolInvocation.signal for cooperative cancellation.
• Propagates a session-scoped abort signal into tool invocations and triggers it on session abort (then resets for future tool calls).
• Adds unit tests validating abort signal behavior and propagation to tool handlers.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
python/copilot/tools.py	Adds AbortSignal/AbortController and attaches an abort signal to ToolInvocation.
python/copilot/session.py	Wires a session-level abort controller into tool invocation execution and triggers it from abort().
python/copilot/init.py	Exposes AbortSignal in the public package API.
python/test_tools.py	Adds tests for abort signal semantics and propagation via ToolInvocation.