[BUG] Desktop preview reports 'Couldn't find this file' for a file the agent just wrote (exists on disk)

App and versions

• Claude Desktop on Windows: Version 1.46388.4 (50e62f), Sep 4, 2026 (About dialog).
• Same machine also has Claude Code CLI 2.1.236 for reference.
• Windows 11 + WSL2 present, but the failing file below is Windows-native — zero WSL involvement.

What issue are you seeing?

The Desktop preview pane reports "Couldn't find this file" for a Markdown file the agent had just written in the same session:

Couldn't find this file. It may have been deleted, or it lives outside the working directory.

The chat transcript card shows the file (18.9KB) and the preview offers "Show in Explorer". The file was written via the agent Write tool to C:\Users\<user>\Documents\....

Independently verified from outside the app: the file exists — 18,870 bytes, newest file in its folder. Screenshot of the app state available on request.

Possibly same root: outside-workspace PNG won't attach/display

Separately, a PNG under a Windows AppData\...\TempState\ path exists and is navigable but will not attach or display in the app. Its bytes were verified independently (full read, matching SHA-256 across environments) and the image renders in a different harness — so this is attach/preview path handling, not file corruption or transport. Filing together since both smell like workspace-root scoping; happy to split.

What is the expected behavior?

Preview and attach resolve files the agent wrote and files that exist at valid paths. If outside-root files are intentionally excluded, the rule should be documented and the UI should offer a copy-in step instead of a dead end.

Repro notes

The September-4 preview incident has rotated out of retained main.log (current log only), so this report rests on the screenshot plus independent file verification. I can re-run a minimal write-then-preview probe on request.