Corrupted terminal commands and performance issues when pasting from clipboard

Issue with SSM session-start presents when modifying a file inside a session and using up and down arrows rapidly... in vi ssm injects A,B,C, or D characters depending on the directional your pressing. In addition pasting a lot of data from clipboard to system it very slow.

Start by reproducing the SSM session-start behavior while editing in vi: rapidly use the arrow keys, then paste a large clipboard payload. Trace the terminal input handling involved in session-start, and consider the work done when arrow keys no longer inject A/B/C/D and large pastes complete without the reported slowdown.

Written by the indexing model from the issue text.