Report errors for git patch types which are not valid

[strawgate]

Right now, create_pull_request and update branch tools are more permissive when called than the actual git patch process is.

Certain activities like merge commits and changes to the tree emit patches that later in safe outputs fails to apply.

We can detect this in the history when the tool is called and return an error to the agent who can correct the situation

[strawgate]

This means: no git merge, no git rebase, no git commit-tree with multiple -p flags.