Move allow_shell from message[0] (static system prompt) to the per-turn
<runtime_prompt> tag alongside mode and approval. This preserves the
DeepSeek prefix cache across shell-access toggles and mode switches,
which previously forced YOLO entry/exit to rebuild the entire prompt.
Changes:
- Delete remove_shell_tool_guidance and 3 other dead functions (~60 lines)
- Remove allow_shell field from PromptSessionContext and StaticPromptCtx
- Remove shell_tools_available dead parameter from compose functions
- Add Shell Policy section to Runtime Policy Reference (static text)
- Extend <runtime_prompt> tag with allow_shell="true|false" attribute
- Update tests: omits→always_keeps, 83/83 prompts tests pass
- Drop dead compose_mode_prompt_with_approval_and_model
Net: message[0] bytes are now stable regardless of shell-access state.
Mode/approval/shell flags all use the same per-turn tag pattern.
zLeoAlex
9206eb9d73