Fetched content stops evaporating — and a writer that deleted fields on every save

Previews fetched a page, showed it, and threw it away. Now they file it. Found a bug on the way that was quietly stripping `internal_only` from real client sources.

• Source-Curation
• Corpus-Building
• Frontmatter-Schema
• Jina
• Data-Loss
• Two-Tier-Fetch
• MemoPop