Claude Desktop "Open" attach picks wrong file content despite showing correct filename in confirmation dialog

**Environment:**
- Windows 11 Home, build 10.0.26200
- Claude Desktop (version: check Settings > About)
- Reproduced across a full shutdown/reboot, not a transient state issue

**Description:**
Right-clicking Open or double-clicking a .csv file in File Explorer launches Claude Desktop and shows a correct "Attach '' to this session?" confirmation dialog naming the actual file clicked. But the content that lands in the chat after clicking Attach is from a different, unrelated file, not the one named in the dialog or the one clicked.

**Steps to reproduce:**
1. In File Explorer, right-click a .csv file and choose Open (or double-click it).
2. Claude Desktop opens and shows "Attach '' to this session?"
3. Click Attach.
4. The content in the chat is from a different file than the one named.

**Confirmed NOT the cause (ruled out directly):**
- File corruption: read the file directly off disk outside any app; content is correct.
- Windows file-type association hijack: checked four times via registry (.md and .csv, both extension-to-progid mapping and the actual shell open command). All clean.
- Stuck app/OS state: persisted across a full shutdown and reboot.

**Context:** started shortly after ~100 duplicate CSV files were downloaded into Downloads in one session (a separate, since-fixed bug in an unrelated tool). The wrong file that gets attached appears to be from that same episode, suggesting a stale reference or cache inside Claude Desktop's own attach/file-picker logic.

**Workaround:** right-click "Open with," choosing Notepad or Excel explicitly, works correctly. Only plain Open/double-click triggers the wrong-content behavior.

Reproduce the issue in Claude Desktop on Windows 11 by opening a CSV from File Explorer and comparing the confirmation filename with the attached content. Then trace the desktop attach/file-picker path for stale file references or caching; done means the selected file's content consistently matches the filename shown and the workaround is no longer needed.

Written by the indexing model from the issue text.