Agent.WorkingDirectory appears not to be writable when run from inside a container

[flcdrg]

Not exactly sure why, but when I run Cake from within a Linux Container (Ubuntu / .NET Core) as part of an Azure Pipelines build, the directory pointed at by Agent.WorkFolder (aka TFBuild.Environment.Agent.WorkingDirectory ) is not writable, such that Cake.TFBuild.Module.TFBuildReportPrinter.WriteToMarkdown is failing to create the tasksummary.md file.

This results in the following error:

========================================
Default
========================================
##[debug]Processed: ##vso[task.logdetail finishtime=02/25/2019 05:00:15;progress=100;result=Succeeded;id=3f293bfc-27b1-42cf-af56-139f503340c8;]update
##[debug]Processed: ##vso[task.logdetail finishtime=02/25/2019 05:00:15;progress=100;state=Completed;result=Succeeded;id=0ffa0556-53ab-4a01-8f8a-c7dd226e3a15;]update
Error: One or more errors occurred. (Access to the path "/__w/tasksummary.md" is denied.)
	Access to the path "/__w/tasksummary.md" is denied.
##[debug]Exit code 1 received from tool '/bin/bash'

(I wasn't having this problem when I was building in a non-container Ubuntu hosted agent)

[flcdrg]

See comments in microsoft/azure-pipelines-agent#2122. Looks like Agent.WorkFolder is not the best place