Use environment defaults for client async config

[liuzemei]

Fixes #621

Summary

• initialize AgentFieldClient with AsyncConfig.from_environment() when no explicit async config is provided
• preserve explicit async_config instances unchanged
• add regression coverage for client-level environment defaults

Tests

• uv run --extra dev pytest tests/test_async_config.py -q
• uv run --extra dev pytest tests/test_client_unit.py tests/test_client_auth.py tests/test_async_config.py -q

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
2 out of 3 committers have signed the CLA.

✅ AbirAbbas
✅ santoshkumarradha
❌ SheldonNeo
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Python	9.4 KB	+4%	0.32 µs	-9%	✓	✓

✓ No regressions detected

[santoshkumarradha]

Thanks for the fix. This brings AgentFieldClient in line with Agent by picking up async defaults from the environment, and the regression tests cover both the env-backed default path and the explicit override path.

I also approved the first-time contributor workflow runs so CI is now moving.

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 84%, aggregate ≥ 85%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.10%	87.40%	↓ -0.30 pp	🟡
sdk-go	91.80%	92.00%	↓ -0.20 pp	🟢
sdk-python	93.73%	93.73%	↑ +0.00 pp	🟢
sdk-typescript	90.20%	90.42%	↓ -0.22 pp	🟢
web-ui	84.94%	84.79%	↑ +0.15 pp	🟡
aggregate	85.74%	85.75%	↓ -0.01 pp	🟡

✅ Gate passed

No surface regressed past the allowed threshold and the aggregate stayed above the floor.

[github-actions]

📐 Patch coverage gate

Threshold: 80% on lines this PR touches vs origin/main (from .coverage-gate.toml:thresholds.min_patch).

Surface	Touched lines	Patch coverage	Status
control-plane	0	—	➖ no changes
sdk-go	0	—	➖ no changes
sdk-python	1	100.00%	✅
sdk-typescript	0	—	➖ no changes
web-ui	0	—	➖ no changes

✅ Patch gate passed

Every surface whose lines were touched by this PR has patch coverage at or above the threshold.

[santoshkumarradha]

Thanks for updating this branch. The code and required test checks look good on my side.

The remaining blocker is still the CLA check. cla-assistant is showing SheldonNeo as the missing signer here: https://cla-assistant.io/Agent-Field/agentfield?pullRequest=632

Once that clears, this should be in good shape to merge.