I'm working primarily in two scenarios: fiction writing and small Python library development. Both follow a top-down design approach, but the current Plan Mode has a critical limitation: it only provides read-only context management. When I try to incrementally refine requirements (e.g., from novel outline to detailed chapter breakdowns, or from module architecture to function signatures), the context gets lost or overwritten. Forcing me to switch back and forth between Plan and Execute modes disrupts the creative/design flow and fragments the thought process.

Describe the solution you'd like
I propose adding a controlled write permission to Plan Mode that generates second-order instructions (design directives) without executing first-order instructions (final code/text generation). This would enable a true top-down workflow within a single mode:

1. Hierarchical Design Tree: Support nesting sub-requirements under parent nodes (e.g., outline → detailed chapter plans → implementation notes) without losing parent context
2. Permission Boundary: Plan Mode can create/modify design documents, interface definitions, and implementation strategies, but never the final deliverable (code/prose)
3. Context Preservation: Sub-requirements should complement, not replace, parent requirements
4. Mode Closure: Complete the entire design chain (outline → detailed plan → implementation specs) inside Plan Mode before explicitly switching to Execute Mode
5. Output Directory: Restrict all second-order output to a designated directory for clean management

Use Cases

Fiction Writing:

1. Generate novel outline in Plan Mode
2. Continue in Plan Mode to break down each chapter into detailed beats
3. Refine character arcs and plot points iteratively
4. Only switch to Execute Mode when ready to write actual prose

Python Library Development:

1. Design module structure and public APIs in Plan Mode
2. Define function signatures and docstrings without implementation
3. Add configuration schemas and error handling strategies
4. Switch to Execute Mode only after all design layers are complete

Describe alternatives you've considered

• Manual context management: Copy-pasting previous context into new prompts is error-prone and inefficient
• Frequent mode switching: Alternating between Plan/Execute modes causes mental context switching and premature generation
• External documentation: Maintaining separate design docs defeats the purpose of an integrated AI-assisted workflow

Additional context
This essentially transforms Plan Mode from a "one-time outline generator" into a "multi-level design workspace," enabling users to stay in the creative/design headspace until they consciously decide to generate the final artifact.