[BUG] Claude Desktop: can't load attachments or read pastes-as-attachments after forced update to 1.21459.0

What's wrong

After Claude Desktop force-updated today, attachments no longer load, and pasted content that gets turned into an attachment (rather than inline text) can't be read either. This is a regression tied directly to the update — confirmed via the app's own update log:

• Platform: Windows, x64
• Previous version: 1.20186.9
• Updated version: 1.21459.0
• Update applied automatically (Squirrel auto-updater), today

Symptoms

1. Attachments fail to load in the conversation.
2. Content pasted into the chat that becomes an attachment (rather than staying inline text) can't be read by the model either — same failure, same trigger.

Reproduction

1. Be on Claude Desktop 1.20186.9 or earlier on Windows.
2. Let the app apply its automatic update to 1.21459.0.
3. Try to attach a file, or paste content large/complex enough that the client turns it into an attachment rather than inline text.
4. Attachment fails to load / isn't readable.

Additional info

This reproduced immediately after the forced update with no other environment changes — same machine, same session pattern that worked before the update.