feat(ai): Implement configurable base system prompt and expose in UI

src/ai_client.py

@@ -143,7 +143,8 @@ _SYSTEM_PROMPT: str = (
 )
 
 _custom_system_prompt: str = ""
-_global_tool_instructions: str = ""
+_base_system_prompt_override: str = ""
+_use_default_base_system_prompt: bool = True
 _project_context_marker: str = ""
 
 def set_custom_system_prompt(prompt: str) -> None:
@@ -151,9 +152,13 @@ def set_custom_system_prompt(prompt: str) -> None:
  global _custom_system_prompt
  _custom_system_prompt = prompt
 
-def set_global_tool_instructions(instructions: str) -> None:
- global _global_tool_instructions
- _global_tool_instructions = instructions
+def set_base_system_prompt(prompt: str) -> None:
+ global _base_system_prompt_override
+ _base_system_prompt_override = prompt
+
+def set_use_default_base_prompt(use_default: bool) -> None:
+ global _use_default_base_system_prompt
+ _use_default_base_system_prompt = use_default
 
 def set_project_context_marker(marker: str) -> None:
  global _project_context_marker
@@ -165,7 +170,10 @@ def _get_context_marker() -> str:
 def _get_combined_system_prompt(preset: Optional[ToolPreset] = None, bias: Optional[BiasProfile] = None) -> str:
  if preset is None: preset = _active_tool_preset
  if bias is None: bias = _active_bias_profile
- base = _global_tool_instructions if _global_tool_instructions.strip() else _SYSTEM_PROMPT
+ if _use_default_base_system_prompt:
+  base = _SYSTEM_PROMPT
+ else:
+  base = _base_system_prompt_override
  if _custom_system_prompt.strip():
   base = f"{base}\n\n[USER SYSTEM PROMPT]\n{_custom_system_prompt}"
  if preset and bias: