Record H2 img2img output-cloud portability boundary

[DeliciousBuding]

Summary: Adds a CPU-only existing-cache review for H2 output-cloud geometry on the existing SD/CelebA img2img response caches. The result is weak or unstable on the admission cache and not distinct from simple distance, so this narrows H2 output-cloud to a Research-side response-strength diagnostic only. No Runtime runner, Platform row, admitted bundle change, model download, GPU task, or img2img sweep is selected.

Checks: review_h2_img2img_output_cloud_portability.py smoke run; python -X utf8 scripts/check_markdown_links.py; python -X utf8 scripts/check_public_surface.py; python -X utf8 scripts/export_admitted_evidence_bundle.py --check; python -X utf8 scripts/run_pr_checks.py.

[gemini-code-assist]

Code Review

This pull request introduces a portability review for H2 output-cloud geometry on image-to-image (img2img) response caches. It includes a new evaluation script, review_h2_img2img_output_cloud_portability.py, and detailed documentation of the findings, which conclude that the geometry is weak or unstable on SD/CelebA caches compared to simple-distance baselines. The project roadmap, reproduction status, and implementation queue have been updated to reflect that this method remains a research-side diagnostic rather than a production candidate. A review comment correctly identified a potential runtime error in the new script when reference metrics are missing and provided a code suggestion to improve robustness.

[gemini-code-assist]

The max() function will raise a ValueError if the generator expression is empty, which occurs if the reference simple-distance-review.json files are missing for both the admission and stability caches. Adding a default value ensures the script remains robust even when reference metrics are unavailable.

Suggested change

	max_simple_distance_auc_delta = max(
	float(packet["comparison"]["output_cloud_minus_best_simple_distance"]["auc"])
	for packet in packets
	if packet["comparison"]["output_cloud_minus_best_simple_distance"] is not None
	)
	max_simple_distance_auc_delta = max(
	(
	float(packet["comparison"]["output_cloud_minus_best_simple_distance"]["auc"])
	for packet in packets
	if packet["comparison"]["output_cloud_minus_best_simple_distance"] is not None
	),
	default=0.0,
	)