Published artifacts deleted server-side without user action on a personal account (no delete UI exists; links were already shared)

## Summary

Three published Claude Code artifacts were deleted server-side with no user action. The owning account is a **personal, self-paid subscription** (no Team/Enterprise workspace, no org admins, no org retention policy, no compliance-API access), so no organization-side mechanism can explain the deletion. The links had already been shared with collaborators over Slack and worked when shared; they now 404 for everyone **including the owner while logged in**.

## Affected artifact URLs

- https://claude.ai/code/artifact/573f1281-2c3f-47fb-9cbe-b177c3d88be3?via=auto_preview
- https://claude.ai/code/artifact/fb60d334-2045-4544-acec-565466b228ef
- https://claude.ai/code/artifact/cfaa9c3d-e189-47a6-a5a7-3931be95adda?via=auto_preview

All three were published from Claude Code CLI sessions in late July / early August 2026 (super-resolution microscopy render previews). Noticed broken 2026-08-18.

## Evidence

1. Each URL returns "artifact not found — it may have been deleted, or it has not been shared with you", fetched while authenticated as the owning account.
2. None of the three IDs appear in the account's artifact gallery (checked via the Artifact tool `list` action with `scope: "all"` — owned and shared).
3. The deletion is **selective**: ~50 other artifacts on the same account, published 2026-07-07 through 2026-08-18, still list and resolve normally.
4. The user never deleted them — and per #74589 there is currently no user-facing delete/unpublish mechanism in the gallery UI at all.
5. Two of the three shared URLs carry `?via=auto_preview` (i.e. Claude auto-published them). If auto-previewed artifacts receive any server-side cleanup/garbage collection, that behavior is undocumented and silently breaks already-shared links.

## Questions

1. By what mechanism were these artifacts deleted?
2. Is there any retention/expiry or GC applied to consumer-account artifacts — in particular auto-published (`via=auto_preview`) ones? If so, what is the window and where is it documented?
3. Can these artifacts (content / version history) be restored?
4. If not restorable, can deletion timestamps be provided so users know how long shared artifact links can be relied on?

Account email available privately on request for investigation.

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Filed on behalf of the account owner from a Claude Code session.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Start by reproducing the three authenticated artifact URLs and the Artifact tool list action with scope "all"; the issue provides those entry points but no repository files or tests. Compare the missing artifacts with the roughly 50 surviving artifacts and investigate the server-side retention or cleanup behavior. Done means the deletion mechanism, retention window, and restoration or deletion-timestamp outcome are documented.

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