Keep author-layout image URLs editor-valid after WordPress materialization

[chubes4]

Problem

Fixture 37 materializes blocks-engine/author-layout with a nested image whose saved block markup retains the relative source website/assets/materialized-svg/inline-svg-453b87c087581ebd.svg. WordPress resolves the editor DOM value to an absolute theme URL, so wp.blocks.validateBlock reports an attribute mismatch and marks the block invalid.

Evidence

• SSI PR: Fix form control topology materialization static-site-importer#760 at 00cfb164
• Blocks Engine: 74fec9e9
• Homeboy run: b280bf88-2257-4915-9d80-f4c52ff6a538
• Fixture: 37-art-gallery-exhibition
• Block: blocks-engine/author-layout
• Mismatch: relative src=website/assets/materialized-svg/inline-svg-453b87c087581ebd.svg vs absolute runtime theme URL

Reproduction:

node tools/run-fixture-matrix.mjs --static-site-importer /path/to/static-site-importer --blocks-engine /path/to/blocks-engine --local --target-fixture 37-art-gallery-exhibition --surface-coverage 6

Acceptance

• Author-layout nested image serialization remains valid after WordPress resolves materialized asset URLs.
• The generic fix applies to URL-bearing nested content without fixture-specific selectors or paths.
• Fixture 37 editor validation reports no author-layout attribute mismatch.

AI Assistance

OpenAI GPT-5.6 Sol via OpenCode ran the seven-surface matrix, analyzed the editor validation evidence, and drafted this report. Chris Huber reviewed the evidence and remains responsible for the issue.