test(examples): regression test for seller_agent PRODUCTS schema compliance (#324)

[bokelley]

Refs #324

Summary

Issue #324 reports that @adcp/client@5.21.1's Ajv oneOf validator falsely flags products 2–5 in seller_agent.py as missing required properties (name, description, publisher_properties, etc.) — fields that are clearly present in the dumped CI response. The Python jsonschema validator confirms all six static products are 3.0.1 spec-compliant; the failures are in the npm-side error reporter, not in the shape we emit.

This PR adds a regression test that anchors that Python-side verdict and guardrails future PRODUCTS additions.

What's in this PR

• tests/test_seller_agent_products_schema.py — 7 test cases:
  • test_full_products_list_passes_response_validation — validates all 6 products as a batch (catches array-level constraints)
  • test_individual_product_passes_response_validation[] — parametrized per product, so a failing product ID appears directly in the pytest node name

Both tests guard against outcome.variant == "skipped" (the silent-pass case when schemas/cache/ is absent).

_PRODUCTS is a copy.deepcopy snapshot at collection time, guarding against seed_pricing_option() mutating per-dict pricing_options contents if an integration test runs in the same process.

What was tested

• pytest tests/test_seller_agent_products_schema.py -v — 7 passed (initial + fixup pass)
• ruff check tests/test_seller_agent_products_schema.py — clean
• mypy tests/test_seller_agent_products_schema.py --ignore-missing-imports — clean

Pre-PR review (initial)

• code-reviewer: approved — two issues flagged in round 1 (variant != "skipped" guard, list() copy); both fixed; round-2 pass found no new blockers, 1 nit (shallow copy leaves per-dict pricing_options mutable)
• dx-expert: approved — 3 nits noted: import path, raw repr vs format_issues(), shallow vs deep copy. None blockers.

Fixup commit — nits addressed (re-trigger via /triage execute on #324)

Three nits from the initial review were addressed in a follow-up commit:

#	Location	Change
1	line 19	Import validate_response + format_issues from public adcp.validation (not internal schema_validator submodule)
2	lines 50, 68	format_issues(outcome.issues) in assert messages for actionable CI output
3	line 35	copy.deepcopy(...) instead of list(...) to guard per-dict contents

Fixup pre-PR review:

• code-reviewer: approved — no blockers; 1 nit (comment could be more precise about which mutations deepcopy guards); pre-existing internal imports in protocols/ are out of scope
• dx-expert: approved — all three nits correctly fixed, no new issues introduced

Triage-managed PR. This bot does not currently iterate on
review comments or PR conversation threads (only on the source
issue). To unblock:

• Push fixup commits directly: gh pr checkout <num> →
  fix → push.
• Or re-trigger: comment /triage execute on the source
  issue.

See adcp#3121
for context.

Session: https://claude.ai/code/session_01XcYd2AQ7o5h5SP2HEpbcXL