TYPO3 Core

While it's know that TYPO3_MODE isn't used anymore in v12, it's quite common that updating extensions might be still required.
Old extensions have checks included like this:

defined('TYPO3_MODE') || die();

This is stopping TYPO3 v12 completely and never shows any hint what could be wrong. The install tool shouldn't be derailed by the missing of this constant, but scanning for it and reporting the need for removal or replacement.
Currently TYPO3 v12 is completely unusable if an extension is still having this check included.

Therefore I plead to include a definition for it at least in the install tool, so that an upgrade wizard could inform about required changes.