Better behavior on entry posting when over the tag limit

[azurelunatic]

Title
Better behavior on entry posting when over the tag limit

Short, concise description of the idea
Instead of giving you no errors when saving, showing no tags, but displaying tags on the edit screen when you're over the tag limit and use mixed existing and new tags on an entry, the system should handle it better.

Full description of the idea
So you have reached or passed the tag limit (if you created more tags than the tag limit before tags were capped, you may be over the limit), and you post an entry. You type in a tag you know you have, and a tag you think you have. You post. Success! You view your entry. No tags! You go to edit entry (not edit tags for some reason, because you don't feel like that today) and lo and behold, your tags are right there in the tags field where they should be. You view edit tags, and there are no tags. You ask Support, and someone tells you that the tags are right there in the entryprops.

This is (now) known bad behavior.

Obviously something instead of this should happen. Please shred the following ideas to pieces and contribute your own if you think of some.

Proposals:

• Post with only the tags that already exist, not preserving any of the attempted tags. (Advantages: posts immediately which is good for Really Weird Clients and post by email. Disadvantages: no record of the tags you were trying to use.)

• Post only with the tags that already exist, but throw an inescapable (no-optout) email and inbox error that contains the tags you were trying to use. (Advantages: preserves tags, good for weird clients. Disadvantages: more notifications that people might ignore.)

• Post entirely without tags, with no error and no attempt at preservation. (Advantage: probably simple to implement. Disadvantages: legion.)

• Post entirely without tags, but sending error messages to email and inbox with the tags you were trying to use, all of them. (Advantages: immediate posting, tags preserved, possibly simple. Disadvantages include no tags, in addition to the above-mentioned problems with notifications.)

• On attempting to post, an error to the effect of:
  
  "The following tag(s) could not be created, as you have 2,926 tags and the current maximum is 1,200:
  • this tag does not exist
  • bunnies
  • why me and frank the goat are homies
  Please go edit before posting."
  
  Advantages: a whole lot of information, consistent with other errors, tags preserved.
  Disadvantages: Complexity to implement, may cause issues with Weird Clients (some clients will take error messages, some aren't so good at it) and/or email posting, entry is not posted immediately.