Yes it is possible and I could see this as a benefit. Just as guitarhack says, DVR's do it all the time. Hell my Tivo keeps a 30min buffer all the time. I could see software doing the same thing.
Here's how to do it:
The DAW would always keep a (pre-determined size in MB) buffer from the sound cards input. Press play and it starts to write to the buffer. When you hit stop, the buffer is kept with all the info on it. However, the moment you press play, the buffer is over-written with new info and keeps all info until you press stop or it reaches the size limit. Repeat endlessly.
Select Options/Keep Buffer.
There ya go!
[edit]
Forgot to answer original question!
No Sonar does nothing close to this.
Workaround?
Always keep your trk armed! Always press R!
: )
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