feat: read-only live view at /view?key=<LIVEVIEW_KEY>

Implements issue #5. Off by default; set LIVEVIEW_KEY in .env to enable.
No JWT required — key-based auth via ?key= query param.
Returns 403 when disabled or key is wrong.
Read-only ReactFlow canvas (pan/zoom, no editing).
Standalone mode loads from localStorage without a key.
Includes 8 backend tests and 9 frontend tests.

backend/app/api/routes/liveview.py

@@ -0,0 +1,40 @@
+from typing import Any
+
+from fastapi import APIRouter, Depends, HTTPException, Query
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.core.config import settings
+from app.db.database import get_db
+from app.db.models import CanvasState, Edge, Node
+from app.schemas.canvas import CanvasStateResponse
+from app.schemas.edges import EdgeResponse
+from app.schemas.nodes import NodeResponse
+
+router = APIRouter()
+
+
+@router.get("", response_model=CanvasStateResponse)
+async def liveview_canvas(
+    key: str | None = Query(default=None),
+    db: AsyncSession = Depends(get_db),
+) -> CanvasStateResponse:
+    """Read-only public canvas endpoint.
+
+    Disabled by default — requires LIVEVIEW_KEY to be set in .env.
+    Always returns 403 when disabled, regardless of the key provided.
+    """
+    if not settings.liveview_key:
+        raise HTTPException(status_code=403, detail="Live view is disabled")
+    if not key or key != settings.liveview_key:
+        raise HTTPException(status_code=403, detail="Invalid live view key")
+
+    nodes = (await db.execute(select(Node))).scalars().all()
+    edges = (await db.execute(select(Edge))).scalars().all()
+    state = await db.get(CanvasState, 1)
+    viewport: dict[str, Any] = state.viewport if state else {"x": 0, "y": 0, "zoom": 1}
+    return CanvasStateResponse(
+        nodes=[NodeResponse.model_validate(n) for n in nodes],
+        edges=[EdgeResponse.model_validate(e) for e in edges],
+        viewport=viewport,
+    )

backend/app/core/config.py

@@ -30,6 +30,11 @@ class Settings(BaseSettings):
     # Leave empty to disable MCP service key auth.
     mcp_service_key: str = ""
 
+    # Live view — optional read-only public canvas endpoint.
+    # Set to a random secret string to enable /api/v1/liveview?key=<value>.
+    # Leave unset (or empty) to keep the feature disabled (default).
+    liveview_key: str | None = None
+
     def _override_path(self) -> Path:
         return Path(self.sqlite_path).parent / "scan_config.json"
 

backend/app/main.py

@@ -5,7 +5,7 @@ from typing import Any
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
-from app.api.routes import auth, canvas, edges, nodes, scan, status
+from app.api.routes import auth, canvas, edges, liveview, nodes, scan, status
 from app.core.config import settings
 from app.core.scheduler import start_scheduler, stop_scheduler
 from app.db.database import init_db
@@ -40,6 +40,7 @@ app.include_router(edges.router, prefix="/api/v1/edges", tags=["edges"])
 app.include_router(canvas.router, prefix="/api/v1/canvas", tags=["canvas"])
 app.include_router(scan.router, prefix="/api/v1/scan", tags=["scan"])
 app.include_router(status.router, prefix="/api/v1/status", tags=["status"])
+app.include_router(liveview.router, prefix="/api/v1/liveview", tags=["liveview"])
 
 
 @app.get("/api/v1/health")