Why: Upload inventory alone did not prove that the attachment-only user message included and persisted all three materials.
Evidence: Real upload IDs match the empty-text POST and the same user artifact_ref parts before and after reload; both live cases pass.
Impact: Stronger acceptance evidence only; retain mock-runner model-quality limits.
Refs: ce-code-review 20261012-165912-cb241b46 #4, UI01/UI04/U5
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