Improve experience for invalid generateRebase responses

[d13]

Missing or incorrect hunks

On rare occasion, the AI provider responds with commits that:

• don't include all the hunks we sent
• include hunk numbers we didn't send
• use the same hunk twice

Our current short-term solution is to provider an error message to the user that explains the AI response was missing changes and to retry again.

Ideally, a better retry solution would be to continue the conversation with another turn, telling the provider that it missed some changes, provide the bad response they sent and ask it to fix it.

A follow-up: #4429

Verification steps

• don't pick the best model because it often succeeds from the first time (pick ollama or an old model of another provider)
• try generating: the action should fail with less frequency than before the fix

[sergeibbb]

@d13

I've separated the second part to another issue, because these parts can obviously go independently. And the second part wasn't specified as well as the first part. Now it's here: #4429