When I type a new task title and/or description, Phabricator should suggest potential duplicates. Here is how Bugzilla does this:
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Restricted Application added a subscriber: Aklapper. · View Herald TranscriptMay 4 2015, 10:54 PM2015-05-04 22:54:21 (UTC+0)
Qgil closed this task as a duplicate of T45: Phabricator should suggest possible duplicates when creating a new task.May 5 2015, 3:49 AM2015-05-05 03:49:30 (UTC+0)