[FEATURE]: Having custom instructions

[Sahil-Gupta584]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Can i pass custom instructions to agent everytime i prompt?
Or maybe we can tweak internal system prompt in starting of each new session

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• [FEATURE]: Support custom system prompt per model in config #18177: Support custom system prompt per model in config (very similar request)
• [FEATURE]: Allow custom system prompts in global, project or custom directories #7101: Allow custom system prompts in global, project or custom directories (very similar request)
• [FEATURE]: Add systemPrompt option to SDK like Claude Agent SDK #7351: Add systemPrompt option to SDK (related)
• [FEATURE]: Inject content to system prompt via CLI flag #16089: Inject content to system prompt via CLI flag (related)
• add optional system prompt environment injection #1894: Add optional system prompt environment injection (related)

Please review these issues and consider adding your input there instead of opening a new one.