docs: define v1 requirements

.planning/REQUIREMENTS.md

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+# Requirements: Chat Agent WebApp
+
+**Defined:** 2026-03-27
+**Core Value:** A working, well-understood AI chat interface — every line of code is intentional and explained
+
+## v1 Requirements
+
+### Chat Core
+
+- [ ] **CHAT-01**: User can type a message and send it to the OpenAI GPT API
+- [ ] **CHAT-02**: User receives the AI response displayed in the chat area
+
+### Conversation Management
+
+- [ ] **CONV-01**: User can create a new conversation
+- [ ] **CONV-02**: User can switch between existing conversations
+- [ ] **CONV-03**: User can delete a conversation
+- [ ] **CONV-04**: Conversations persist to JSON files and survive app restarts
+
+### Message Display
+
+- [ ] **DISP-01**: AI responses render as formatted markdown (headings, lists, bold, links)
+- [ ] **DISP-02**: Code blocks in AI responses display with syntax highlighting
+- [ ] **DISP-03**: User can copy a message to clipboard
+
+### UI/Layout
+
+- [ ] **UI-01**: App has sidebar with conversation list and main chat area
+- [ ] **UI-02**: Chat area has text input with send button
+- [ ] **UI-03**: App layout is responsive across screen sizes
+
+### Code Quality
+
+- [ ] **CODE-01**: Every Blazor concept introduced has inline comments explaining what and why
+- [ ] **CODE-02**: Each phase introduces one concept incrementally (tutorial-style progression)
+
+## v2 Requirements
+
+### Streaming
+
+- **STRM-01**: AI responses stream token-by-token in real time
+- **STRM-02**: User can cancel an in-progress AI response
+- **STRM-03**: Loading/typing indicator shows during AI generation
+
+### Agentic Workflows
+
+- **AGNT-01**: LangChain integration for workflow orchestration
+- **AGNT-02**: RAG pipeline for document retrieval
+- **AGNT-03**: MCP server integration for tool use
+
+### Enhanced Features
+
+- **ENH-01**: Auto-generated conversation titles from first message
+- **ENH-02**: System prompt configuration per conversation
+- **ENH-03**: Model selector (GPT-4o, GPT-4o-mini, etc.)
+- **ENH-04**: Dark/light theme toggle
+- **ENH-05**: Auto-scroll during message display
+- **ENH-06**: Visual distinction between user and AI messages (styled bubbles)
+
+## Out of Scope
+
+| Feature | Reason |
+|---------|--------|
+| Authentication/login | Single user, no auth needed |
+| Database storage | JSON files sufficient for personal use |
+| Deployment/hosting | Local development only for v1 |
+| Multi-user support | Personal tool |
+| OAuth/third-party login | Not needed |
+| Voice input/output | Complexity, not core to chat value |
+| Image/multimodal input | Defer to v2+ |
+| Real-time collaboration | Single user |
+| Mobile app | Web-first |
+
+## Traceability
+
+Which phases cover which requirements. Updated during roadmap creation.
+
+| Requirement | Phase | Status |
+|-------------|-------|--------|
+| CHAT-01 | — | Pending |
+| CHAT-02 | — | Pending |
+| CONV-01 | — | Pending |
+| CONV-02 | — | Pending |
+| CONV-03 | — | Pending |
+| CONV-04 | — | Pending |
+| DISP-01 | — | Pending |
+| DISP-02 | — | Pending |
+| DISP-03 | — | Pending |
+| UI-01 | — | Pending |
+| UI-02 | — | Pending |
+| UI-03 | — | Pending |
+| CODE-01 | — | Pending |
+| CODE-02 | — | Pending |
+
+**Coverage:**
+- v1 requirements: 14 total
+- Mapped to phases: 0
+- Unmapped: 14 ⚠️
+
+---
+*Requirements defined: 2026-03-27*
+*Last updated: 2026-03-27 after initial definition*