ESC ESC does not save the half-typed command in history

### Describe the feature or problem you'd like to solve

In the middle of typing a prompt, use ESC ESC to stash what's typed in history

### Proposed solution

There are so many times where I'm in the middle of typing a long prompt, and I realize I need to do something else first. A common one is I realized after typing half my prompt that I forgot to do /add-dir for an important directory. I want to be able to do ESC ESC to clear the prompt and *add my prompt in progress to the history not just erase it*. This is a huge pain point for me in transitioning from CC. I so often just instinctively hit ESC ESC and curse at myself "what did I just do!" because I really needed to save all the text I just typed out.

### Example prompts or workflows

"I'm typing this really long prompt out with very detailed instructions of everything I want done. As I'm typing, I realize I need to pull in a file from another project that I have not yet done /add-dir." ESC ESC
Expected: Save all the text I typed in the history, I can get back to it just by hitting up arrow.
Actual: All of the text I typed before hitting ESC ESC is gone forever.

### Additional context

_No response_

Start by tracing the ESC ESC prompt-handling path and how the CLI writes and reads command history. Reproduce the described workflow, then verify that clearing a half-typed prompt preserves it and that pressing the up arrow restores the saved text.

Written by the indexing model from the issue text.