The agent write-stamp idiom — `...(isAgent ? { <source>: 'agent', <chat>: aiChatId } : {})`
— was hand-reimplemented at every REST write site, so each new path risked a
wrong literal or a forgotten aiChatId. Extract a single
`agentSourceFields(provenance, sourceKey, chatKey)` next to AuthProvenanceData and
call it at the 5 uniform spread sites:
- comment.service create -> createdSource / aiChatId
- page.service create/update/orphan-move/move -> lastUpdatedSource / lastUpdatedAiChatId
Sites that must CLEAR the source on a non-agent action keep their own conditional
(comment un-resolve writes an explicit null), and the collab persistence path keeps
its sticky-window logic — both noted in the helper's doc.
Behavior-preserving (the helper returns the identical object/`{}`). Typecheck
clean; server comment/page/auth/collab suites 246 pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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