feat(testing): make SellerA2AClient event drain configurable

[sangilish]

Summary

Refs #698.

This makes the A2A seller test harness event-drain budget configurable. SellerA2AClient.invoke() now accepts a keyword-only max_events argument that defaults to the existing hard cap of 32, so current callers keep the same behavior while tests for noisier A2A flows can opt into a larger drain budget.

What changed

• Added max_events: int = 32 to SellerA2AClient.invoke().
• Replaced the hardcoded 32-event drain loop with the caller-provided cap.
• Updated the exhaustion error to report both timeout_seconds and max_events.
• Added regression coverage for default-cap exhaustion and success with a larger cap.

Testing

Passed:

• uv run python -m pytest tests/test_seller_a2a_client.py -q
• uv run ruff check src/adcp/testing/harness.py tests/test_seller_a2a_client.py
• uv run mypy src/adcp/testing tests/test_seller_a2a_client.py
• uv run python -m pytest -q

Attempted broader checks:

• uv run ruff check fails on pre-existing unrelated lint issues outside this PR's files (26 errors reported).
• uv run mypy src tests fails on pre-existing unrelated type issues outside this PR's files (1688 errors in 160 files reported).

[github-actions]

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[sangilish]

I have read the IPR Policy

[github-actions]

IPR Policy — signed

Thanks, @sangilish. Your agreement to the IPR Policy is recorded at signatures/ipr-signatures.json and applies to all AAO repositories.

[sangilish]

I have read the IPR Policy

[bokelley]

Thanks, @sangilish — IPR acknowledgment noted.

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Generated by Claude Code

[bokelley]

Thanks @sangilish — IPR acknowledgment noted.

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Generated by Claude Code

[sangilish]

This is ready for review now. CI is green, and I kept the change scoped to #698 with the default behavior preserved.

[bokelley]

Acknowledged — thanks for the heads-up. Noted that CI is green, default cap is preserved, and scope is limited to #698. No action needed from this routine; the PR is queued for human review.

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Generated by Claude Code

[bokelley]

Looks good. Updated against main and rechecked the touched A2A harness surfaces locally.

[bokelley]

Superseded by #829, which merged the same patch from a base-repo branch so the required CodeQL check could run. Thanks again @sangilish.