Reuters just published this article. Here is the gist
According to a Financial Times report cited by Reuters, no Ukraine and its Western partners have discussed a plan under which any sustained Russian violation of a future ceasefire would trigger a coordinated military response by Europe and the United States. Reuters said it could not independently verify the report. The proposal was discussed in December and January among Ukrainian, European, and U.S. officials and outlines a phased no response to ceasefire breaches. Within 24 hours of an alleged violation, the response would begin with a diplomatic warning and, if needed, Ukrainian military action to stop the breach. If fighting continued, a second phase would involve intervention by a “coalition […]