Inherit prompt instructions when appropriate

[basicthinker]

Is your feature request related to a problem? Please describe.

Currently, instructions are not inherited from previous prompts. But if you are discussing a commit message, for example, you won't repeat /commit_message in each prompt.

Describe the solution you'd like

If the current prompt has instructions, disregard any from previous prompts. Otherwise, inherit the instructions of the latest previous prompt (reference or parent if no reference).