Artifact database tools gain a view level, required if_version and clearer access messages

What

Published artifacts, shareable pages or apps Claude can create, can keep a small database that Claude reads and writes with the read_db and write_db actions. Several things about those actions change.

• as_level, which lets Claude act as a certain kind of user, now accepts "view" for someone who can only view the artifact, alongside "interact" (a signed-in viewer who can use it) and "admin" (someone who can edit it). A write_db at "view" is refused before anything is sent, even for your own data/users subtree.
• if_version, a version number that stops a write from overwriting changes made since you read the document, is now required for any write to a document that already exists. It used to be described as optional. Without it the write is refused until the document is read.
• In a batch, if_version is required for every entry whose document already exists. A batch missing one writes nothing, and the whole batch body is capped at 1 MiB.
• read_db results now include a meId value and note when me in a path was resolved to the caller's user id.
• Write results now say who can read the change: this differs for 'private' collections and for pages with access rules. Before, they always said every viewer sees it. By default, rows in a data/users subtree are readable only by that one user, not even by the artifact's owner, unless the page's access rules say otherwise.
• When the server confirms the requested as_level was applied (levelConfirmed), a not-found result is described as what a user at that level really sees, and other results drop the "unconfirmed" caveat.
• Write and batch-write errors now include the server's reason, including when a request fails with invalid_argument ("the server could not accept the request as shaped").
• Saved-document listings name extra ids more compactly and explain that '~' in an id is spelled '@' in the file name.

Why

Claude can now check what a view-only visitor sees and gets more definite answers about access. Writes that skip if_version on existing documents, and batches that used to succeed without it, will now be refused.