test: add example corpus non-vacuity guard

[Brad-Edwards]

Summary

Adds an explicit non-vacuity guard to the SDL example scenario loading suite so a stale or relocated example-corpus root fails loudly instead of collecting zero parametrized cases.

Requirement UIDs

• ASR-504

Related Issues

Closes #7

ADR Impact

• No ADR required

Changes

• Added test_example_scenario_corpus_is_nonempty beside the example scenario parametrization in implementations/python/tests/test_scenarios.py.
• Kept the existing marker-discovered EXAMPLES_DIR and load_scenario() path unchanged.
• Verified the SDL testing documentation already points at examples/scenarios/, so no documentation edit was needed.

Test Plan

• cd implementations/python && uv run --extra dev pytest tests/test_scenarios.py -q (27 passed)
• ACES_REQUIREMENT_UID=ASR-504 pre-commit run --all-files
• ACES_REQUIREMENT_UID=ASR-504 implementations/python/.venv/bin/python tools/check_repo_policy.py
• ACES_REQUIREMENT_UID=ASR-504 implementations/python/.venv/bin/python tools/check_requirement_governance.py (exited 0 with Ground Control unavailable skip)
• ACES_REQUIREMENT_UID=ASR-504 implementations/python/.venv/bin/python tools/verify_all.py
• ACES_REQUIREMENT_UID=ASR-504 uv tool run --from 'nox[uv]==2026.4.10' nox -f noxfile.py -s verify

The full verify runs passed. Their requirement-governance subcheck also exited 0 in Ground Control unavailable skip mode.

Ground Control Checks

• Latest implemented-diff GRC screening recorded not_security_relevant
• gc_assert_quality_gates passed for ASR-504
• Pre-push codex review and test-quality review completed cleanly

Traceability

• IMPLEMENTS: ASR-504 <- implementations/python/tests/test_scenarios.py
• TESTS: ASR-504 <- implementations/python/tests/test_scenarios.py, ASR-504 <- implementations/python/tests/test_example_schema_conformance.py, ASR-504 <- implementations/python/tests/test_sdl_models.py, ASR-504 <- implementations/python/tests/test_sdl_realworld.py, ASR-504 <- implementations/python/tests/test_sdl_fuzz.py, ASR-504 <- implementations/python/tests/test_sdl_validator.py

Checklist

• Code follows project coding standards
• No business logic in API layer
• Domain layer has no framework imports
• Envers @Audited on new entities if applicable
• Changelog fragment: N/A — test-only diff; repo plan rules forbid changelog fragments
• Architectural docs updated if stack, package structure, or key behaviors changed

Documentation

Verified unchanged: no documentation update required for the test-only diff, and docs/explain/sdl/testing.md already documents repo-root examples/scenarios/.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud