To build for macOS, Linux, and Windows efficiently in Azure DevOps YAML, use Job Templates for shared build logic and Stage Templates to orchestrate these jobs across different OS agents, defining OS-specific pool agents within the job template or calling the job template within a looping stage for maximum reuse and minimal duplication, especially when parameterized. Start by creating a reusable job template with OS-agnostic steps (e.g., dotnet build), then define a stage template that calls this job template for each OS, using vmImage to specify ubuntu-latest, windows-latest, and macos-latest, allowing for a single, parameterized pipeline definition.
Note:
A DevOps job template is a reusable blueprint (often a YAML file in platforms like Azure DevOps) that defines standardized stages, jobs, tasks, and parameters for automated build, test, and deployment pipelines, promoting consistency, reducing duplication, and improving maintainability across projects. It acts as a framework, allowing teams to quickly spin up new pipelines with pre- defined best practices for security, compliance, and workflows, ensuring smooth collaboration between development and IT.
Reference:
https://techcommunity.microsoft.com/blog/healthcareandlifesciencesblog/azure-devops-pipelines- templates-tasks-and-jobs/3712459

To entirely remove unwanted files from a repository's history you can use either the git filter-branch command or the BFG Repo-Cleaner open source tool.
Reference:
https://docs.github.com/en/github/authenticating-to-github/keeping-your-account-and-data-secure/removing-sensitive-data-from-a-repository

Flaky tests present a barrier to finding real problems, since the failures often don't relate to the changes being tested. A flaky test is a test that provides different outcomes, such as pass or fail, even when there are no changes in the source code or execution environment.
Reference:
https://docs.microsoft.com/en-us/azure/devops/pipelines/test/flaky-test-management?view=azure-devops

Explanation:
Box 1: subscribe
To start monitoring all Git repositories in a project, use the following slash command inside a channel:
/azrepos subscribe [project url]
Box 2: https://dev.azure.com/contoso/contoso-app
You can also monitor a specific repository using the following command:
/azrepos subscribe [repository url]
The repository URL can be to any page within your repository that has your repository name.
For example, for Git repositories, use:
/azrepos subscribe https://dev.azure.com/myorg/myproject/_git/myrepository Reference:
https://docs.microsoft.com/en-us/azure/devops/repos/integrations/repos-slack

Explanation:
Restore the working tree files with the content from the given tree. It is common to specify the source tree by naming a commit, branch or tag associated with it.
https://www.git-tower.com/learn/git/commands/git-restore