This adds the `-E/--use-existing-tasks` flag to the `fuzzy` or `chooser` selectors. For example: ./mach try fuzzy -E This queries the Treeherder API to find your latest try push, then any tasks that exist on that push, but aren't explicitly selected this time, will be replaced with those older tasks. You can also run: ./mach try fuzzy -E task-id=<task id> Where `<task id>` is the id of the Decision task from the push you would like to use as the base. Differential Revision: https://phabricator.services.mozilla.com/D200380