Feature request: import/create comment threads on Artifacts (round-trip serialization)

Feature request

Allow programmatically creating/importing comment threads on a published Artifact — the write-side counterpart of the existing comments read action on the Artifact tool.

Current behavior

• Comment threads on Artifacts can be read (action: "comments") and replied to (action: "reply", on activated threads), so Claude can export a durable transcript of threads to disk.
• There is no way to import them: threads live server-side, attached to a specific artifact URL, and can only be created by viewers in the UI.

Why it matters

We use commentable Artifact pages as review surfaces for a multi-agent build workflow (each work track publishes a review page; the human leaves pinned comment threads; Claude acts on them). We serialize each page to disk in-repo: source file + artifact-URL binding + a one-way comment export. That covers durability, but the threads themselves aren't portable:

• If a page is ever recreated at a new URL (lost binding, new account/workspace, migrating a project), all live threads are orphaned — the export is a flat transcript, not restorable state.
• Backup/restore of a project's review history can't round-trip.

Requested capability

Either of these would solve it:

1. An import_comments / create_thread action on the Artifact tool (thread anchor selector + comment list with authorship/timestamps, clearly marked as imported), or
2. An export format (JSON) whose re-import onto a same-content artifact restores threads with their anchors and resolved/open state.

Workaround today

One-way markdown export of threads committed to the repo, and treating the artifact-URL binding file as precious so republishing always targets the same URL.