feat: implement cross-device reading progress synchronization using SignalR and remove legacy quiz generation services.

.agents/skills/blazor-hybrid-bridge.md

@@ -24,6 +24,10 @@ description: Standards for cross-platform compatibility (Web & MAUI Hybrid)
   - Use `IPlatformService.GetDeviceContext()` to determine `DeviceType` (Phone, Tablet, Desktop).
   - Adapt UI layout dynamically based on the context (e.g., sidebars on Tablet/Desktop, bottom navigation on Phone).
 
+- **Real-time & Events (SignalR / UI):**
+  - **Debouncing**: Implement trailing-edge debouncing using `CancellationTokenSource` and `Task.Delay` for high-frequency UI events (like scrolling). Do not just drop events inside a time window, as the final state might be lost.
+  - **Dependency Isolation**: Blazor WebAssembly (`Web.Client`) cannot reference projects that require `Microsoft.AspNetCore.App` (like SignalR Hubs). Keep SignalR abstractions in `UI.Shared` and the Hub implementation strictly on the server (`Infrastructure` or `Web.New`).
+
 - **Dependency Injection:**
   - Register implementations in `MauiProgram.cs` for mobile and `Program.cs` for web.
   - Components in `NexusReader.UI.Shared` must only depend on the interfaces.

.agents/skills/nexus-clean-architecture.md

@@ -16,6 +16,7 @@ description: Clean Architecture & CQRS implementation for .NET 10 with Blazor Hy
   - **Queries**: Read-only operations, return `Task<Result<T>>`.
   - **Commands**: State-changing operations, return `Task<Result>` or `Task<Result<T>>`.
   - **Handlers**: Located in `Application` layer, grouped by feature (e.g., `Queries/Reader/...`).
+  - **Client-Server Boundaries**: DO NOT execute MediatR handlers directly from WASM/MAUI clients if the handler relies on server-only infrastructure (e.g., `AppDbContext`, `IHubContext`). Instead, the client must trigger an API or SignalR endpoint, and the server dispatches the MediatR command.
 
 - **Functional Error Handling:**
   - Mandatory use of `FluentResults`.
@@ -35,4 +36,7 @@ description: Clean Architecture & CQRS implementation for .NET 10 with Blazor Hy
 
 - **Cross-Platform Strategy:**
   - Maximize code sharing in `NexusReader.UI.Shared`.
-  - Use `IPlatformService` (or similar abstractions) for native features, implemented in `Infrastructure.Mobile` or Maui projects.
+  - Use `IPlatformService` (or similar abstractions) for native features, implemented in `Infrastructure.Mobile` or Maui projects.
+
+- **Code Validation (CRITICAL):**
+  - **Mandatory Build Verification**: After any code change, the agent MUST run `dotnet build` on the solution. The agent must verify that the build completes with `Exit code: 0` and without errors before concluding the task or requesting user feedback.

.agents/skills/nexus-code-review.md

@@ -0,0 +1,30 @@
+---
+name: nexus-code-review
+description: Code Review Checklist and Standards for NexusReader SaaS
+---
+# NexusReader Code Review Standards
+
+When conducting or receiving a code review for NexusReader, ensure the implementation adheres to the following critical architectural and performance standards:
+
+## 1. Architectural Boundaries (CQRS & Blazor Hybrid)
+- [ ] **Client vs. Server Execution**: MediatR handlers that depend on server-side infrastructure (`AppDbContext`, `IHubContext`, secrets) MUST NOT be executed directly from client environments (WASM/MAUI).
+- [ ] **Dependency Leakage**: Ensure `NexusReader.Web.Client` (WASM) does not reference `NexusReader.Infrastructure` if the infrastructure requires `Microsoft.AspNetCore.App` framework references.
+- [ ] **SignalR Bridges**: Client-initiated state changes should be sent via SignalR `SendAsync` to a server Hub, which then dispatches the internal `MediatR` command.
+
+## 2. Event Handling & Debouncing
+- [ ] **High-Frequency UI Events**: UI actions like scrolling, resizing, or typing must be debounced.
+- [ ] **Trailing-Edge Debounce**: Use a `CancellationTokenSource` and `Task.Delay` to ensure the *last* event in a rapid sequence is executed. Do not use simple time-window drops, as they result in lost final states.
+- [ ] **Async Void**: Ensure UI event handlers do not use `async void` unless they are top-level framework event bindings, and even then, they must catch all exceptions.
+
+## 3. SignalR & Real-Time Contexts
+- [ ] **Authentication Context**: Do not rely on `IHttpContextAccessor` inside MediatR handlers triggered by SignalR Hubs. Use `Context.UserIdentifier` directly from the Hub and pass it as a command parameter.
+- [ ] **Connection State**: Always check `HubConnection.State == HubConnectionState.Connected` before attempting to send messages from the client.
+- [ ] **Targeted Broadcasting**: Use SignalR `Groups` (e.g., `$"User_{userId}"`) to broadcast updates only to the devices owned by the relevant user.
+
+## 4. Performance & Scalability
+- [ ] **Database Write Contention**: High-frequency telemetry (like reading progress) should ideally be batched or cached in-memory before writing to SQL, unless real-time persistence is strictly required.
+- [ ] **Memory Leaks**: Ensure all components and services that subscribe to events (e.g., `OnProgressReceived`, JS Observers) implement `IDisposable` or `IAsyncDisposable` and properly unsubscribe.
+
+## 5. Standard Nexus Guidelines
+- [ ] **Result Pattern**: Ensure all application logic returns `Result` or `Result<T>` via FluentResults. No exceptions for control flow.
+- [ ] **AI Prompts**: Ensure changes to AI logic do not bypass the `PromptRegistry` or token estimation limits defined in `AiSettings`.