[kentonv]

Note that sandstorm.io (and Cap'n Proto) was written 100% after I left Google, so I'm not sure if that's a great example.

I would not recommend working on a future startup while still at Google, unless the work is 100% open source and approved. If it's open source, you'll have an easier time getting it approved if you let Google keep copyright. This should be fine because they cannot retroactively revoke the license, so your startup will be able to use it under the terms of the open source license.

If you're writing proprietary code, you are putting your future startup at risk. It's not just that Google might come after you (this is actually unlikely, since it's bad PR for Google), but you may have a hard time getting investors if your IP rights aren't in order. Investors do care about this stuff.

California law does not work well as a defense since Google essentially claims that all code relates to its business in some way.