Basically porting the CX1 fixes done as part of T163344: Do a root-cause analysis on CX outage during dc switch and get it back online to CX2. Especially, changes from https://gerrit.wikimedia.org/r/#/c/350200/:
Improve CX draft saving logic
- Increase retry delay after each failure
- Limit automatic retry attempts to 5, after which user action is needed to attempt saving again.
- If a save has failed, prevent other save requests other than the the retry attempt
- Throttle auto-saving: before it would save when a three second pause is detected. This could lead the worst case of a save happening every three seconds. Changed this to use throttle instead, which saves every 15 seconds (taking a very conservative value here on purpose) regardless whether there is a pause in the writing or not.