initial commit

backend/API/Hubs/IPrinterClient.cs

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+namespace Extrudex.API.Hubs;
+
+/// <summary>
+/// Strongly-typed client interface for the SignalR PrinterHub.
+/// Defines the methods that the server can invoke on connected clients
+/// to push real-time printer status updates.
+/// </summary>
+public interface IPrinterClient
+{
+    /// <summary>
+    /// Pushes a full printer status update to all clients subscribed
+    /// to a specific printer's group. Fired whenever a printer's
+    /// operational status changes (e.g., Idle → Printing, Offline → Idle).
+    /// </summary>
+    /// <param name="printerId">The unique identifier of the printer that changed.</param>
+    /// <param name="status">The new status value (e.g., "Idle", "Printing", "Offline", "Error", "Paused").</param>
+    /// <param name="lastSeenAt">Timestamp (UTC) of when this status was last observed.</param>
+    /// <returns>A Task that completes when the client has processed the update.</returns>
+    Task PrinterStatusChanged(Guid printerId, string status, DateTime? lastSeenAt);
+
+    /// <summary>
+    /// Pushes a lightweight heartbeat to confirm that a printer is still
+    /// reachable and its connection is alive. Useful for dashboards that
+    /// display online/offline indicators without requiring a full status payload.
+    /// </summary>
+    /// <param name="printerId">The unique identifier of the printer.</param>
+    /// <param name="isActive">Whether the printer is currently active and available for jobs.</param>
+    /// <param name="lastSeenAt">Timestamp (UTC) of the last telemetry received from the printer.</param>
+    /// <returns>A Task that completes when the client has processed the heartbeat.</returns>
+    Task PrinterHeartbeat(Guid printerId, bool isActive, DateTime? lastSeenAt);
+}