feat(compose): honour deploy.replicas

Sources/ComposeEngine/ComposeOrchestrator.swift

@@ -87,9 +87,14 @@ public struct ComposeOrchestrator: Sendable {
         return "\(sanitize(project))-\(sanitize(service))-\(replica)"
     }
 
-    /// How many replicas a service runs: the `--scale` value when given, else `scale:`, else 1.
+    /// How many replicas a service runs. The `--scale` value wins, then a
+    /// non-default `scale:`, then `deploy.replicas`, then 1.
     public static func replicaCount(for serviceName: String, in project: ComposeProject, scales: [String: Int]) -> Int {
-        max(1, scales[serviceName] ?? project.services[serviceName]?.scale ?? 1)
+        let service = project.services[serviceName]
+        if let scaled = scales[serviceName] { return max(1, scaled) }
+        if let scale = service?.scale, scale != 1 { return max(1, scale) }
+        if let replicas = service?.deploy?.replicas { return max(1, replicas) }
+        return 1
     }
 
     /// The image reference for a service: its `image:` when present, otherwise

Sources/ComposeEngine/Models/ComposeModels.swift

@@ -798,18 +798,23 @@ public struct HealthCheckConfig: Sendable, Codable, Equatable {
 /// The deploy section (only resource limits are honored).
 public struct DeployConfig: Sendable, Codable, Equatable {
     public var resources: DeployResources?
+    /// Number of containers to run for the service (used when `scale:` is not set).
+    public var replicas: Int?
 
-    public init(resources: DeployResources? = nil) {
+    public init(resources: DeployResources? = nil, replicas: Int? = nil) {
         self.resources = resources
+        self.replicas = replicas
     }
 
     enum CodingKeys: String, CodingKey {
         case resources
+        case replicas
     }
 
     public init(from decoder: Decoder) throws {
         let c = try decoder.container(keyedBy: CodingKeys.self)
         resources = try c.decodeIfPresent(DeployResources.self, forKey: .resources)
+        replicas = try c.decodeIfPresent(Int.self, forKey: .replicas)
     }
 }
 

Tests/ComposeEngineTests/ComposeMultiFileTests.swift

@@ -94,3 +94,29 @@ final class ComposeReplicaTests: XCTestCase {
         XCTAssertEqual(ComposeOrchestrator.replicaCount(for: "db", in: project, scales: ["db": 0]), 1)
     }
 }
+
+final class ComposeDeployReplicasTests: XCTestCase {
+    func testDeployReplicasUsedWhenScaleIsDefault() throws {
+        let project = try ComposeParser().parse(yaml: """
+        services:
+          web:
+            image: nginx
+            deploy:
+              replicas: 3
+        """)
+        XCTAssertEqual(ComposeOrchestrator.replicaCount(for: "web", in: project, scales: [:]), 3)
+        XCTAssertEqual(ComposeOrchestrator.replicaCount(for: "web", in: project, scales: ["web": 2]), 2)
+    }
+
+    func testExplicitScaleBeatsDeployReplicas() throws {
+        let project = try ComposeParser().parse(yaml: """
+        services:
+          web:
+            image: nginx
+            scale: 4
+            deploy:
+              replicas: 3
+        """)
+        XCTAssertEqual(ComposeOrchestrator.replicaCount(for: "web", in: project, scales: [:]), 4)
+    }
+}