What
The Read tool is how Claude Code opens a file for the model. It has a shortcut: if the model already read the same part of a file in full, it can skip reading it again. That shortcut now applies only if the earlier read's content was actually placed in the model's context, the text the model can see. Several kinds of reads are now marked as not having reached the model, and those do not trigger the shortcut.
Why
Before, the model could be told it already had a file's contents when it never saw them, and so work without them. Now a file that never reached the model gets read properly.