Artifact db capability: reads/writes silently fail (no data persists) across networks, browsers, devices

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When using a Claude Artifact with the db capability declared, data does not persist and reads always return empty — even though the artifact tool's own read_db/write_db confirm the documents exist server-side.

Symptoms:

• Adding an item via the app's own UI appears to save (optimistic UI update), but disappears after a page refresh.
• All read queries return empty results, with no error banner shown.
• Reproduced on a brand-new artifact with default (no custom) db capability settings — not specific to one artifact.
• Reproduced on: normal Chrome tab, Incognito mode, home WiFi, and mobile data (cellular) — ruling out network/extension causes.
• Browser console shows this error on every page load:

Unsafe attempt to load URL http://160.79.104.10:6080/php/urlblock.php?args=... from frame with URL https://claude.ai/code/artifact/... . Domains, protocols and ports must match.

This looks like a platform-side issue establishing the db capability's backend connection for my account, not an artifact code bug.

Affected artifact: https://claude.ai/code/artifact/8daf8fda-ea31-4372-ad40-e5985d9eab4c

What Should Happen?

Data entered or read through an Artifact's db capability should persist to the server and be readable again after a page refresh, on any network/browser/device — matching what the artifact tool's own read_db/write_db actions show is actually stored.

Error Messages/Logs

Steps to Reproduce

1. Publish a Claude Artifact with capabilities: {db: {}} declared.
2. Open the published artifact URL in a normal Chrome tab (also reproduced in Incognito mode, on home WiFi, and on mobile cellular data).
3. Use the artifact's own UI to add/save an item (it appears immediately via optimistic UI update).
4. Refresh the page.
5. The item is gone, and any db read (e.g. window.claude.use('db').then(db => db.collection(...).get())) returns 0 documents — even though the artifact tool's own read_db/write_db actions (used from the Claude session that built the artifact) confirm the documents exist server-side.
6. Reproduced this on a brand-new, separate artifact with no custom db rules — not specific to one artifact.
7. Browser console shows this error on every load: "Unsafe attempt to load URL http://160.79.104.10:6080/php/urlblock.php?args=... from frame with URL https://claude.ai/code/artifact/... . Domains, protocols and ports must match."

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.260 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_