In other words, I want this Target to be invoked just once a the start and end of the whole build session, not for each individual project that might be built as part of that session.
Another way to put is it that when hitting Build (F7) in Visual Studio I would like to invoke my custom Target at the very beginning and end of the build, regardless of what was built (and whether or not it was successful).
Is this possible? If not, are there alternatives to using MSBuild Targets that would allow me to call my process at the start and end of every Visual Studio build?
To execute a solution-wide Before and After targets, you would create two MSBuild project files named "after.<SolutionName>.sln.targets" and "before.<SolutionName>.sln.targets" in the same folder as your solution.
To do this on all solutions, you would drop your custom solution-level after targets files into the path $(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\SolutionFile\ImportBefore\ or $(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\SolutionFile\ImportAfter. When those solutions are built, it will import all project files in these folders if they exist.
To verify the above, open a command prompt and navigate to the folder containing your solution file. Type "SET MSBuildEmitSolution=1". Then run msbuild.exe <SolutionName>. You will see that msbuild has saved the metadata project files <SolutionName>.sln.metaproj and <SolutionName>.sln.metaproj.tmp in the same path as your solution.
View the <Import /> declarations at the top and bottom of the file and you'll notice the conditional imports that allow you to declare solution-specific before and after targets, or global solution-specific before and after targets.
Edit:
It appears that this would only be applicable to command line or team builds, but not from within Visual Studio.
I added this to my After.Solution.sln.targets file:
From the command line: Bananas!
On a TFS build: Bananas!
Visual Studio: No bananas :(