Notes to fix a CDP port problem in windows:
If Antigravity launches the browser, but it can’t navigate to url, likely CDP port isn’t working.
So, check if CDP port 9222 is already being used or is already reserved:
List currently in use: netstat -ab
List reserved ranges: netsh int ipv4 show excludedportrange tcp
Mine had reserved range: 9145 9244
So I killed a process reserving many ranges: net stop winnat
Then the browser tool worked.