Tests/logger coverage

[AnandKrishnamoorthy1]

Summary

This PR implements a robust unit test suite for the AgentFieldLogger, achieving 100% coverage for the module (exceeding the 95% requirement for this task). It also modernizes the SDK’s project configuration by removing legacy support for Python 3.9.

Testing

• ./scripts/test-all.sh
• Additional verification:
  Executed uv run python -m pytest tests/test_execution_logger.py -v
  Verified 16/16 tests passing locally on Python 3.13.
  Confirmed agentfield/logger.py reached 100% line coverage via pytest-cov.

Checklist

[x] I updated documentation where applicable (Docstrings added to new tests).
[x] I added or updated tests.
[x] I updated pyproject.toml to remove Python 3.9 (EOL Oct 2025).
[x] I updated CHANGELOG.md (or this change does not warrant a changelog entry).

Related issues

Fixes #400

[CLAassistant]

All committers have signed the CLA.

[github-actions]

Performance

SDK	Memory	Δ	Latency	Δ	Tests	Status
Python	7.9 KB	-13%	0.32 µs	-9%	✓	✓

✓ No regressions detected

[github-actions]

📊 Coverage gate

Thresholds from .coverage-gate.toml: per-surface ≥ 86%, aggregate ≥ 88%, max per-surface regression ≤ 1.0 pp, max aggregate regression ≤ 0.50 pp.

Surface	Current	Baseline	Δ
control-plane	87.30%	87.30%	→ +0.00 pp	🟡
sdk-go	90.70%	90.70%	→ +0.00 pp	🟢
sdk-python	93.63%	93.63%	↑ +0.00 pp	🟢
sdk-typescript	92.56%	92.56%	→ +0.00 pp	🟢
web-ui	90.02%	90.01%	↑ +0.01 pp	🟢
aggregate	89.02%	89.01%	↑ +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	0	—	➖ no changes
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.

[AbirAbbas]

will run ci then merge