EXC_BREAKPOINT crash when asking Apple Intelligence while a PDF is open

[AlvaroFranco]

Describe the bug

We've received several reports of crashes when users invoke Apple Intelligence (by double-tapping the inner bar) while a PDF is open.

/Library/Caches/com.apple.xbs/Sources/UIIntelligenceSupport_Sim/UIIntelligenceSupport/API/Elements/Element Content Types/IntelligenceElement+Document.swift:106: Fatal error: URL is not a file URL: http://localhost:58818/26FDADF6-67B8-42E8-885D-DE0F629A296E/00048362.pdf

We've been able to reproduce this both in our app and in the Readium TestApp.

We think that the Apple Intelligence framework expects a file URL, whereas Readium uses a local server to serve the book content.

How to reproduce?

1. Open a PDF book
2. Make sure Apple Intelligence is enabled on the device
3. Double tap on the iOS inner bar (the one used to close the apps)
4. When the text field prompts, write something
5. App is currently crashing

Readium version

3.6.0

OS version

26.2.0

Testing device

iPhone 17 Pro (simulator)

Environment

macOS: 26.1
platform: arm64
Xcode 26.1.1
Build version 17B100

Additional context

No response