Recursive sync watcher stops tracking computed

[skirtles-code]

Vue version

3.5.6

Link to minimal reproduction

https://play.vuejs.org/#eNp9Uctqw0AM/BWxlzjgOC19QXBCH4TSHtrS9rhQ3I2cOFnvmn04KcH/Xq2N0xxKbtLMSMxIe3ZXVUntkU1YaoUpKgcWna9mXBVlpY2DPRjMY9hmTqxiELqsvMMFNJAbXcKAZgdccSW0sg4MTIM8Ohv2iCCkH4qiIUxnYJI6kx5JwlW7NhIxRHXL7bkCKHJqYQbnw66HfmQ0Cm3DVROTr1x6u5rAwP4oMYCG9qXjLgO5p8ZhWcnMIXUAe8oBTQOjUIlQpd/eOa3gVshCbKacBfM3nM0edTruOJpMx0drWMycpVx5sUzWViu6WmuQsxCxkGheK1dQbs4mvXXOMin19rnFnPEY97hYodj8g6/tLmCcvRm0aGrk7MC5zCzRdfT84wV3VB/IUi+8JPUJ8h2tlj547GT3Xi3I9pGudfvU/r5Qy0873zlUtg8VjLY/aPWc0fsfTkT/s3uRXPa/oyt+1WjCTjrgRXKVXLPmFzJo0y8=

Steps to reproduce

Just click the button.

What is expected?

The rendered values should be 1.

What is actually happening?

The rendered values are 6.

System Info

No response

Any additional comments?

This changed in 3.5.6. In 3.5.5 and earlier it renders 1, as expected.

I found this while investigating #11956. I still don't know what causes the memory leak, but after staring at #11944 for a bit I noticed the potential problem I've reported here.

This is what I believe is happening...

When a computed is notified, the NOTIFIED flag gets set for both ComputedRefImpl and its dep. These are queued in a batch. When endBatch() is called it handles the dep first, clearing the NOTIFIED flag from the dep and then calling trigger(). But the NOTIFIED flag is still set for the ComputedRefImpl, so it can't be notified while trigger() is running.

I used watch with flush: 'sync' in the reproduction, as that was the most direct way to take advantage of the mismatched flags. I'm not sure whether there's a more 'normal' way to hit this timing issue.