[Cowork] Regression since 10 Sep 2026: skills can no longer be saved as a full .skill package; only SKILL.md-only `propose_skills` card, `references/` un-updatable

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?

In Cowork, updating a skill with its reference files stopped working on 10 Sep 2026 between the morning and the afternoon (Europe/Paris). In the morning, the session built a full .skill package (SKILL.md + references/ + scripts/). It was delivered as a file card with Save skill → Upload and replace. From the afternoon on, the only publish path offered is the propose_skills review card, which replaces SKILL.md only. The session instructions now also tell the model not to hand over a packaged skill file. I've reproduced it in 4 sessions in a row, from the afternoon of 10 Sep through 11 Sep.

Consequences:

• There's no in-session way to add, update or delete files under references/ or scripts/.
• Editing a references/ file from a session changes only the session's snapshot. Nothing reaches the account store (checksums were unchanged in a session started afterwards), yet the model reports success.
• Large skills are blocked: a ~277 KB SKILL.md can't safely be resent whole through the card.

What Should Happen?

As on the morning of 10 Sep: a skill update can be saved as a full package (SKILL.md + references/ + scripts/) from a Cowork session. Either restore the .skill → Save skill / Upload and replace card, or let propose_skills carry reference/script files.

Error Messages/Logs

Steps to Reproduce

1. In the Claude desktop app (Windows), start a Cowork task.
2. Ask Claude to update an existing personal skill, including a change to a file under references/.
3. Observe: only a propose_skills card (SKILL.md only) is offered, with no .skill file / Save skill card.
4. Save the card, then start a new session and check the reference file: it is unchanged.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Cowork session on the morning of 10 Sep 2026 (Claude Code version not recorded)

Claude Code Version

2.1.268 (Claude Code) — Cowork cloud session; Claude desktop app 1.52386.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

Cowork (Claude desktop app 1.52386.0, Windows x64, Electron 44.2.0). Cowork runs Claude Code in a cloud session, so there is no terminal.

Last working: Cowork sessions on the morning of 10 Sep 2026 (Europe/Paris). It broke the same afternoon without any local update, so it's probably a server-side change.

Related: #68071 (see my comment there: https://github.com/anthropics/claude-code/issues/68071#issuecomment-5633086321).