MacOS file watcher missing add events

[davidmorgan]

package:watcher tests on MacOS started failing with dev SDK, which handily ties the change to a very recent one, which means it's almost certainly

https://dart-review.googlesource.com/c/sdk/+/451260

you can see the new failures here

https://github.com/dart-lang/tools/actions/runs/18311397921/job/52140618323?pr=2197

I didn't dig into them yet but at first glance it looks like there used to be add events emitted that are no longer emitted, for example

subdirectories notifies when a subdirectory is replaced by a file (failed)
  Expected: should do the following in any order:
            • emit an event that is remove new/file.txt
            • emit an event that is add newer/file.txt
            • emit an event that is remove old
            • emit an event that is add new
    Actual: <Instance of 'StreamQueue<WatchEvent>'>
     Which: emitted • remove /private/var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/dart_test_TgMobG/new/file.txt
                    • add /private/var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/dart_test_TgMobG/new
                    • remove /private/var/folders/q0/wmf37v850txck86cpnvwm_zw0000gn/T/dart_test_TgMobG/old
                    x Stream closed.

note that the absolute paths mentioned in the test failures are not related to the change, the test deals with correctly matching the temp directory if possible.

As it happens I am currently working on this code so I can help figure out exactly what changed if needed.