[BUG] Cowork (Linux/WSL2): new project never prompts for directory; in-session folder not persisted

Summary

On Claude Desktop for Linux (WSL2), the Cowork project flow has three related problems:

1. Creating a new project never prompts for a directory (on Windows the same version shows a location prompt). The project folder is silently created under the folder that happened to be mounted as session context, with no visible indication.
2. Adding a folder inside a session is not persisted to the project. Local state confirms the binding is stored per session, not per project (see evidence below).
3. coworkUserFilesPath is ignored — it points to a directory that does not even exist on disk, yet project folders are created elsewhere.

Environment

• Claude Desktop 1.34493.1 (.deb package)
• Ubuntu 26.04 LTS on WSL2 (kernel 6.18.35.2-microsoft-standard-WSL2), WSLg 1.0.79
• Same behavior before and after fixing the environment (D-Bus session bus + xdg-desktop-portal available and verified working, gnome-libsecret password store active), so this is not a missing-portal issue.

Evidence

Folder binding is stored per session, not per project — ~/.config/Claude/local-agent-mode-sessions/<account>/<org>/remote-session-spaces.json:

{
  "entries": [
    {
      "sessionId": "session_01H3Ue5tdC8gY6vpLB33PEP3",
      "folders": ["/home/valdecir/workdir/cowork/brain"],
      "memoryEnabled": false
    }
  ]
}

Configured files path is ignored (directory does not exist):

"coworkUserFilesPath": "/home/valdecir/Claude"   # ~/Claude does not exist

The new project folder was created inside the previously mounted context folder (~/workdir/cowork/), matching the behavior described in #67330.

Expected

• New project creation should prompt for (or at least clearly display and honor) the destination directory, as on Windows.
• A folder added to a project should persist as project context across sessions.
• coworkUserFilesPath should be honored as the default project root.

Related

• #76694 — same "Choose a folder" loss reported on macOS after the Chat/Cowork merge; this report confirms the regression on Linux/WSL2.
• #67330 — project folder created inside currently-mounted context folder (closed as not planned; behavior still present in 1.34493.1).