Teams that deal with automatically-created Alertmanager tasks will sometimes want to move the task to a subproject/milestone of their main team board - e.g., a board for a team's current sprint - in order to be able to deal with the task more effectively within Phabricator (and within teams' established task-management workflows).
Currently, though, the software behind @phaultfinder (https://github.com/knyar/phalerts/, if I'm not mistaken) doesn't consider subprojects/milestones when trying to work out whether or not a task for a given alert already exists. This results in duplicate tasks for the same issue being created, which then have to be merged into the originally-created task; which in turn increases task noise/work required. (see e.g., T395892#10880018)
This task therefore proposes that the software behind @phaultfinder is modified to also search any milestones/subprojects of a base project, when checking to see whether or not a task for a given alert already exists.
In terms of implementing this, looking at https://github.com/knyar/phalerts/blob/master/phalerts.py, it seems like there might be a few possible options for how to go about it (assuming that the repo owner is happy to accept a PR to enable this behaviour). The simplest that I can think of (right now, off the top of my head) would be to simply remove the lines phalerts.py#L166-L169, which appear to limit the result of the maniphest.search API query to tasks which are specifically tagged with the (base) project provided. Phabricator Maniphest search already seems to include subprojects & milestones when searching by a base project (e.g., this search that filters by Language and Product Localization includes tasks that are tagged with LPL Essential); so if this filtering was removed from phalerts upstream, it seems like @phaultfinder might be able to find tasks within milestones/subprojects with no further changes needed.
(Disclaimer: there might be side effects to this idea that I haven't immediately thought of!)