fix: restore context vars in resolve_tool endpoint

[flowjzh]

Summary

Fix context var propagation in resolve_tool endpoint for uvicorn 0.39.0+.

Problem

Uvicorn PR #2742 fixed contextvar loading
in version 0.39.0. Previously, p.Server.current was accessible in the resolve_tool
endpoint, but after uvicorn 0.39.0 it became unavailable.

This breaks choice providers that depend on p.Server.current, causing:

RuntimeError: No server available in current context

Solution

Restore context vars in the resolve_tool endpoint, following the same pattern
used in the call_tool endpoint:

# Restore context vars for same-process hosted mode
for var, value in self.context_vars.items():
    var.set(value)

This ensures p.Server.current is accessible regardless of uvicorn version.

Testing

• Tested with uvicorn 0.38.0 (before fix)
• Tested with uvicorn 0.39.0+ (after fix)
• Choice providers now work correctly in both versions

References

• Related uvicorn change: explicitly start ASGI run with empty context Kludex/uvicorn#2742
• Similar implementation in call_tool endpoint (line ~716)

[kichanyurd]

Good catch, I bet this manifested in the usage of choice provider. Merged!

[Kludex]

I've reverted the changes in Uvicorn. It will be available in the next release (in a few minutes).