fix(grpc): default to native dns resolver on macos

[sicoyle]

Description

grpc's bundled c-ares resolver frequently ignores macos dns config, cancelling lookups that resolve fine system-wide and failing with StatusCode.UNAVAILABLE "DNS query cancelled", even for reachable endpoints. Defferring to the os resolver (getaddrinfo on mac) fixes it, so mac users get reliable connectivity out of the box without setting an env var for this.

only changes for mac, not windows or linux.

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #[issue number]

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation

[Copilot]

Pull request overview

This PR aims to improve out-of-the-box gRPC connectivity reliability on macOS by defaulting gRPC’s DNS resolver to the OS-native resolver (via the GRPC_DNS_RESOLVER environment variable), while leaving behavior unchanged on other platforms.

Changes:

• Add macOS-only import-time defaulting of GRPC_DNS_RESOLVER=native when the variable is not already set.
• Introduce unit tests validating darwin vs non-darwin behavior and preservation of explicitly configured resolver values.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
dapr/__init__.py	Sets GRPC_DNS_RESOLVER to native on macOS (when unset) during import dapr.
tests/test_grpc_dns_resolver_default.py	Adds unit tests for the new macOS DNS resolver defaulting behavior.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.13%. Comparing base (bffb749) to head (b968b72).
⚠️ Report is 173 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1125      +/-   ##
==========================================
- Coverage   86.63%   82.13%   -4.50%     
==========================================
  Files          84      116      +32     
  Lines        4473     9609    +5136     
==========================================
+ Hits         3875     7892    +4017     
- Misses        598     1717    +1119     

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