Cancelling a Package installation leads to invisible compilation errors preventing the user to enter Play Mode when the “Cancel” button is clicked, and does not actually cancel the package install as it appears in the Project after the Editor is restarted

Steps to reproduce:

1. Create a new Unity project using the Universal 3D template
2. Enable AI toolbar button (Burger button > Services > AI)
3. Click the AI toolbar button and select "Agree and install Unity AI"
4. When loading bar appears, click the "Cancel" button
5. Enter Play Mode
6. Observe the Console window
7. Repeat step 3
8. Observe the Editor
9. Restart the Editor
10. Click the AI toolbar button
11. Observe the Editor

Actual results: Cancelling the package installation leads to invisible compilation errors that prevent user from entering Play Mode (compilation errors are not visible in the Console window), trying to install the same package again does not do anything, and when the Editor is restarted the package appears to be installed

Expected results: The "Cancel" button should cancel the package installation, or if that is not possible, it should at least prevent from invisible errors/breakage. If the "Cancel" button does not cancel the package installation, maybe there shouldn't be a cancel button at all

Reproducible with versions: 6000.0.70f1, 6000.3.11f1, 6000.4.0b11, 6000.5.0a8

Tested on (OS): MacOS Silicon Tahoe 26.2

Notes:

• Reproduces with other packages as well