[excursion] Deduplicate persisted attachment IDs
Codex excursion, unverified.
Summary
Persisted chat attachments now collapse duplicate attachment IDs by keeping the latest chip. Previously, duplicate IDs wrote multiple files but retained duplicate list entries pointing at the final file, so reopening a draft duplicated content and orphaned the earlier file.
Validation
git diff --check- Added
ChatDraftAttachmentsTests.duplicateAttachmentIdsKeepOnlyTheLatestChip. - Swift tests and macOS app builds were not run locally; use the fleet compile-check.
No capture: persistence-only change.
Agent session: cosmic-gray
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Summary by cubic
Persisted chat attachments now collapse duplicate attachment IDs by keeping the latest chip. Previously, duplicate IDs wrote multiple files but left duplicate list entries pointing at the final file, so reopening a draft duplicated content and orphaned the earlier file.
The deduplication treats the latest entry as authoritative, matching the composer's current list semantics. Added ChatDraftAttachmentsTests.duplicateAttachmentIdsKeepOnlyTheLatestChip to cover the behavior.