Phase 2: Chat & AI Core — Claude API streaming, chat UI, admin context

Backend:
- Chat, Message, ContextFile models + Alembic migration
- Chat CRUD with per-user limit enforcement (max_chats)
- SSE streaming endpoint: saves user message, streams Claude response,
  saves assistant message with token usage metadata
- Context assembly: primary context file + conversation history
- Admin context CRUD (GET/PUT with version tracking)
- Anthropic SDK integration with async streaming
- Chat ownership isolation (users can't access each other's chats)

Frontend:
- Chat page with sidebar chat list + main chat window
- Real-time SSE streaming via fetch + ReadableStream
- Message bubbles with Markdown rendering (react-markdown)
- Auto-growing message input (Enter to send, Shift+Enter newline)
- Zustand chat store for streaming state management
- Admin primary context editor with unsaved changes warning
- Updated routing: /chat, /chat/:chatId, /admin/context
- Enabled Chat and Admin sidebar navigation
- English + Russian translations for all new UI

Infrastructure:
- nginx: disabled proxy buffering for SSE support
- Added ANTHROPIC_API_KEY and CLAUDE_MODEL to config

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/api/v1/admin.py

@@ -0,0 +1,33 @@
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.api.deps import require_admin
+from app.database import get_db
+from app.models.user import User
+from app.schemas.chat import ContextFileResponse, UpdateContextRequest
+from app.services import context_service
+
+router = APIRouter(prefix="/admin", tags=["admin"])
+
+
+@router.get("/context", response_model=ContextFileResponse | None)
+async def get_primary_context(
+    _admin: Annotated[User, Depends(require_admin)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    ctx = await context_service.get_primary_context(db)
+    if not ctx:
+        return None
+    return ContextFileResponse.model_validate(ctx)
+
+
+@router.put("/context", response_model=ContextFileResponse)
+async def update_primary_context(
+    data: UpdateContextRequest,
+    admin: Annotated[User, Depends(require_admin)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    ctx = await context_service.upsert_primary_context(db, data.content, admin.id)
+    return ContextFileResponse.model_validate(ctx)

backend/app/api/v1/chats.py

@@ -0,0 +1,103 @@
+import uuid
+from typing import Annotated
+
+from fastapi import APIRouter, Depends, Query, status
+from fastapi.responses import StreamingResponse
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.api.deps import get_current_user
+from app.database import get_db
+from app.models.user import User
+from app.schemas.chat import (
+    ChatListResponse,
+    ChatResponse,
+    CreateChatRequest,
+    MessageListResponse,
+    MessageResponse,
+    SendMessageRequest,
+    UpdateChatRequest,
+)
+from app.services import chat_service
+from app.services.ai_service import stream_ai_response
+
+router = APIRouter(prefix="/chats", tags=["chats"])
+
+
+@router.post("/", response_model=ChatResponse, status_code=status.HTTP_201_CREATED)
+async def create_chat(
+    data: CreateChatRequest,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    chat = await chat_service.create_chat(db, user, data.title)
+    return ChatResponse.model_validate(chat)
+
+
+@router.get("/", response_model=ChatListResponse)
+async def list_chats(
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+    archived: bool | None = Query(default=None),
+):
+    chats = await chat_service.get_user_chats(db, user.id, archived)
+    return ChatListResponse(chats=[ChatResponse.model_validate(c) for c in chats])
+
+
+@router.get("/{chat_id}", response_model=ChatResponse)
+async def get_chat(
+    chat_id: uuid.UUID,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    chat = await chat_service.get_chat(db, chat_id, user.id)
+    return ChatResponse.model_validate(chat)
+
+
+@router.patch("/{chat_id}", response_model=ChatResponse)
+async def update_chat(
+    chat_id: uuid.UUID,
+    data: UpdateChatRequest,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    chat = await chat_service.update_chat(db, chat_id, user.id, data.title, data.is_archived)
+    return ChatResponse.model_validate(chat)
+
+
+@router.delete("/{chat_id}", status_code=status.HTTP_204_NO_CONTENT)
+async def delete_chat(
+    chat_id: uuid.UUID,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    await chat_service.delete_chat(db, chat_id, user.id)
+
+
+@router.get("/{chat_id}/messages", response_model=MessageListResponse)
+async def list_messages(
+    chat_id: uuid.UUID,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+    limit: int = Query(default=50, le=200),
+    before: uuid.UUID | None = Query(default=None),
+):
+    messages = await chat_service.get_messages(db, chat_id, user.id, limit, before)
+    return MessageListResponse(messages=[MessageResponse.model_validate(m) for m in messages])
+
+
+@router.post("/{chat_id}/messages")
+async def send_message(
+    chat_id: uuid.UUID,
+    data: SendMessageRequest,
+    user: Annotated[User, Depends(get_current_user)],
+    db: Annotated[AsyncSession, Depends(get_db)],
+):
+    return StreamingResponse(
+        stream_ai_response(db, chat_id, user.id, data.content),
+        media_type="text/event-stream",
+        headers={
+            "Cache-Control": "no-cache",
+            "Connection": "keep-alive",
+            "X-Accel-Buffering": "no",
+        },
+    )

backend/app/api/v1/router.py

@@ -1,10 +1,14 @@
 from fastapi import APIRouter
 
 from app.api.v1.auth import router as auth_router
+from app.api.v1.chats import router as chats_router
+from app.api.v1.admin import router as admin_router
 
 api_v1_router = APIRouter(prefix="/api/v1")
 
 api_v1_router.include_router(auth_router)
+api_v1_router.include_router(chats_router)
+api_v1_router.include_router(admin_router)
 
 
 @api_v1_router.get("/health")