feat(print): route print jobs through a local agent, fall back to TCP

Phase 2. NetworkPrinterService now builds the ESC/POS bytes (as before) and
dispatches them via a new router: if the receipt/kitchen/station printer is mapped
to a PrintDevice whose agent is online, the bytes are sent to that agent over the
hub and we await its ack; otherwise it falls back to a direct TCP connection (raw
IP), so existing on-prem/reachable printers keep working unchanged. Adds nullable
mapping columns Branch.ReceiptPrintDeviceId / KitchenPrintDeviceId and
KitchenStation.PrintDeviceId (additive migration), plus TestPrintDeviceAsync for
testing an agent printer. The cloud can now reach LAN/USB printers it never could.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Meezi.API/Services/Printing/NetworkPrinterService.cs

@@ -22,6 +22,7 @@ public interface IPrinterService
         string? stationId = null,
         CancellationToken ct = default);
     Task<PrintResult> TestPrintAsync(string printerIp, int port, CancellationToken ct = default);
+    Task<PrintResult> TestPrintDeviceAsync(string cafeId, string deviceId, CancellationToken ct = default);
 }
 
 public class NetworkPrinterService : IPrinterService
@@ -29,17 +30,20 @@ public class NetworkPrinterService : IPrinterService
     private readonly AppDbContext _db;
     private readonly IOrderService _orders;
     private readonly ReceiptBuilder _receiptBuilder;
+    private readonly IPrintAgentRegistry _agents;
     private readonly ILogger<NetworkPrinterService> _logger;
 
     public NetworkPrinterService(
         AppDbContext db,
         IOrderService orders,
         ReceiptBuilder receiptBuilder,
+        IPrintAgentRegistry agents,
         ILogger<NetworkPrinterService> logger)
     {
         _db = db;
         _orders = orders;
         _receiptBuilder = receiptBuilder;
+        _agents = agents;
         _logger = logger;
     }
 
@@ -49,13 +53,16 @@ public class NetworkPrinterService : IPrinterService
         if (ctx is null)
             return PrintResult.Fail("ORDER_NOT_FOUND");
 
-        if (string.IsNullOrWhiteSpace(ctx.Value.branch.ReceiptPrinterIp))
+        var branch = ctx.Value.branch;
+        if (string.IsNullOrWhiteSpace(branch.ReceiptPrintDeviceId) && string.IsNullOrWhiteSpace(branch.ReceiptPrinterIp))
             return PrintResult.Fail("PRINTER_NOT_CONFIGURED");
 
         var bytes = _receiptBuilder.BuildReceipt(ctx.Value.printCtx);
-        return await SendToPrinterAsync(
-            ctx.Value.branch.ReceiptPrinterIp!,
-            ctx.Value.branch.ReceiptPrinterPort ?? 9100,
+        return await DispatchAsync(
+            cafeId,
+            branch.ReceiptPrintDeviceId,
+            branch.ReceiptPrinterIp,
+            branch.ReceiptPrinterPort ?? 9100,
             bytes,
             ct);
     }
@@ -122,18 +129,21 @@ public class NetworkPrinterService : IPrinterService
                 ? null
                 : stations.FirstOrDefault(s => s.Id == group.Key);
 
+            string? deviceId;
             string? ip;
             int port;
             string? stationLabel = null;
 
-            if (station is not null && !string.IsNullOrWhiteSpace(station.PrinterIp))
+            if (station is not null && (!string.IsNullOrWhiteSpace(station.PrintDeviceId) || !string.IsNullOrWhiteSpace(station.PrinterIp)))
             {
+                deviceId = station.PrintDeviceId;
                 ip = station.PrinterIp;
                 port = station.PrinterPort;
                 stationLabel = station.Name;
             }
-            else if (!string.IsNullOrWhiteSpace(ctx.Value.branch.KitchenPrinterIp))
+            else if (!string.IsNullOrWhiteSpace(ctx.Value.branch.KitchenPrintDeviceId) || !string.IsNullOrWhiteSpace(ctx.Value.branch.KitchenPrinterIp))
             {
+                deviceId = ctx.Value.branch.KitchenPrintDeviceId;
                 ip = ctx.Value.branch.KitchenPrinterIp;
                 port = ctx.Value.branch.KitchenPrinterPort ?? 9100;
             }
@@ -147,7 +157,7 @@ public class NetworkPrinterService : IPrinterService
             var bytes = _receiptBuilder.BuildKitchenTicket(
                 ctx.Value.printCtx with { StationName = stationLabel },
                 itemsOnly);
-            var result = await SendToPrinterAsync(ip!, port, bytes, ct);
+            var result = await DispatchAsync(cafeId, deviceId, ip, port, bytes, ct);
             if (result.Success)
                 anyPrinted = true;
             else
@@ -166,6 +176,66 @@ public class NetworkPrinterService : IPrinterService
         return await SendToPrinterAsync(printerIp.Trim(), port, bytes, ct);
     }
 
+    public async Task<PrintResult> TestPrintDeviceAsync(string cafeId, string deviceId, CancellationToken ct = default)
+    {
+        var device = await _db.PrintDevices.AsNoTracking()
+            .FirstOrDefaultAsync(d => d.Id == deviceId && d.CafeId == cafeId, ct);
+        if (device is null)
+            return PrintResult.Fail("DEVICE_NOT_FOUND");
+        if (!_agents.IsOnline(device.AgentId))
+            return PrintResult.Fail("AGENT_OFFLINE");
+
+        var bytes = _receiptBuilder.BuildTestPage();
+        var outcome = await _agents.SendJobAsync(device.AgentId, new PrintJobRequest(device.SystemName, bytes), ct);
+        return outcome.Success ? PrintResult.Ok() : PrintResult.Fail("AGENT_PRINT_FAILED", outcome.Error);
+    }
+
+    /// <summary>
+    /// Send bytes to a printer, preferring a local print agent when one is mapped and
+    /// online (the only way to reach a LAN/USB printer from the cloud); otherwise fall
+    /// back to a direct TCP connection (on-prem deployments / reachable printers).
+    /// </summary>
+    private async Task<PrintResult> DispatchAsync(
+        string cafeId,
+        string? deviceId,
+        string? ip,
+        int port,
+        byte[] bytes,
+        CancellationToken ct)
+    {
+        if (!string.IsNullOrWhiteSpace(deviceId))
+        {
+            var device = await _db.PrintDevices.AsNoTracking()
+                .FirstOrDefaultAsync(d => d.Id == deviceId && d.CafeId == cafeId, ct);
+
+            if (device is not null && _agents.IsOnline(device.AgentId))
+            {
+                var outcome = await _agents.SendJobAsync(
+                    device.AgentId, new PrintJobRequest(device.SystemName, bytes), ct);
+                if (outcome.Success)
+                {
+                    _logger.LogInformation("Printed {Bytes} bytes via agent {Agent} → {Printer}",
+                        bytes.Length, device.AgentId, device.SystemName);
+                    return PrintResult.Ok();
+                }
+                _logger.LogWarning("Agent print failed ({Printer}): {Error}", device.SystemName, outcome.Error);
+                // Only surface the failure if there's no IP to fall back to.
+                if (string.IsNullOrWhiteSpace(ip))
+                    return PrintResult.Fail("AGENT_PRINT_FAILED", outcome.Error);
+            }
+            else if (string.IsNullOrWhiteSpace(ip))
+            {
+                return PrintResult.Fail("AGENT_OFFLINE");
+            }
+            // Agent offline/missing but an IP is configured → fall through to TCP.
+        }
+
+        if (!string.IsNullOrWhiteSpace(ip))
+            return await SendToPrinterAsync(ip!.Trim(), port, bytes, ct);
+
+        return PrintResult.Fail("PRINTER_NOT_CONFIGURED");
+    }
+
     private async Task<(Branch branch, ReceiptPrintContext printCtx)?> BuildContextAsync(
         string cafeId,
         string orderId,