[BUG] Cowork: tasks in a project no longer see other chats/tasks from the same project (regression, July 2026)

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) 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?

This report concerns Claude Cowork (desktop app), not the Claude Code CLI.

Until roughly a week ago (~July 18, 2026), a Cowork task started inside a project could reference context from other chats/tasks in the same project. On July 25, 2026, I explicitly asked a Cowork task to check another chat in the same project and it could not — it behaves as if the rest of the project doesn't exist, with no awareness of previous conversations, decisions, or context.

No app reinstall, settings change, or account change on my side in that window. The change coincides with the July 2026 memory redesign / unified Chat+Cowork projects rollout described in the release notes.

Support docs are currently inconsistent on this: "Organize your tasks with projects in Claude Cowork" says "Memory is enabled for Cowork projects", while "Use Claude's chat search and memory to build on previous context" says memory "is not currently available for Cowork" and doesn't list Cowork as a chat-search surface.

Impact: project-based workflows are broken — every new task starts from zero and all cross-task context has to be re-pasted manually.

Possibly related issues (context/history loss in Cowork): #45076, #42890, #33130, #38459.

### What Should Happen?

A new Cowork task started inside a project should be able to use context from previous chats/tasks in the same project, as it could until approximately July 18, 2026 — by referencing prior conversations.

### Error Messages/Logs

```shell
No error messages — Cowork simply responds as if the project had no other chats and asks for context that was already established in earlier conversations.
```

### Steps to Reproduce

1. Open a project in Claude Cowork (desktop app) that contains several previous chats/tasks with established context.
2. Start a new Cowork task inside that project.
3. Ask Claude to check or reference something discussed in one of the earlier chats in the same project.
4. Claude cannot access any other chat in the project and answers as if the project were empty.

### Claude Model

Opus

### Is this a regression?

Yes, this worked in a previous version

### Last Working Version

Unknown — Claude Desktop auto-updates. Last confirmed working approximately July 18, 2026.

### Claude Code Version

N/A — this is Claude Cowork in the Claude Desktop app (auto-updated, latest version as of July 25, 2026), not the Claude Code CLI.

### Platform

Other

### Operating System

Windows

### Terminal/Shell

Other

### Additional Information

Environment details:
- App: Claude Desktop (Cowork mode), auto-updated to the latest version available as of July 25, 2026
- OS: Windows 11 Pro N, version 21H2 (OS build 22000.2538)
- Plan: Max 5x
- Timezone/locale: Europe/Warsaw (pl)

Timeline:
- Last confirmed working: approximately July 18, 2026
- First confirmed broken: July 25, 2026, when I explicitly asked a Cowork task to check another chat in the same project

This report concerns Claude Cowork in the Claude Desktop app rather than the Claude Code CLI, and names no repository files or tests. Reproduce on Windows 11 by asking a new Cowork task in a populated project to reference an earlier chat; done means the task can access and use prior project conversations consistently.

Written by the indexing model from the issue text.