feat(plan-77): add priority validation and document error types

- Add priority field validation (high/medium/low, case-insensitive)
- Add ConfigurationError.invalidPriority case
- Document error types in README-vsock-relays.md
- Add priority validation tests (valid, invalid, nil cases)
- Fix test imports to use ContainerComposeCore module
- Update Plan 77 with quality assessment findings

Author: amazon1148

Sources/Container-Compose/Networking/RelayConfigurationLoader.swift

@@ -43,6 +43,7 @@ public struct RelayConfigurationLoader {
         case invalidPort(UInt32)
         case missingTarget(String)
         case conflictingPort(UInt32, String)
+        case invalidPriority(String)
 
         public var description: String {
             switch self {
@@ -54,6 +55,8 @@ public struct RelayConfigurationLoader {
                 return "Relay in service '\(service)' requires 'target' for inter-container routing"
             case .conflictingPort(let port, let service):
                 return "Port \(port) already in use by service '\(service)'"
+            case .invalidPriority(let priority):
+                return "Invalid priority: '\(priority)'. Must be 'high', 'medium', or 'low' (case-insensitive)"
             }
         }
     }
@@ -109,6 +112,14 @@ public struct RelayConfigurationLoader {
                     throw ConfigurationError.missingTarget(serviceName)
                 }
 
+                // Validate priority (if provided)
+                if let priority = relayConfig.priority {
+                    let validPriorities = ["high", "medium", "low"]
+                    guard validPriorities.contains(priority.lowercased()) else {
+                        throw ConfigurationError.invalidPriority(priority)
+                    }
+                }
+                
                 let loaded = LoadedRelay(
                     serviceName: serviceName,
                     type: supportedType,

Tests/Container-Compose-Tests/Integration/ComposeSchemaMappingTests.swift

@@ -1,5 +1,5 @@
 import XCTest
-@testable import Container_Compose
+@testable import ContainerComposeCore
 
 // MARK: - Compose YAML Schema Mapping Tests (Plan 77 Phase 6)
 

Tests/Container-Compose-Tests/Networking/NetworkTraceTests.swift

@@ -1,5 +1,5 @@
 import XCTest
-@testable import Container_Compose
+@testable import ContainerComposeCore
 
 // MARK: - Network Trace Tests (Plan 77 Phase 3)
 

Tests/Container-Compose-Tests/Networking/RelayConfigurationLoaderTests.swift

@@ -1,5 +1,5 @@
 import XCTest
-@testable import Container_Compose
+@testable import ContainerComposeCore
 
 // MARK: - Relay Configuration Loader Tests (Plan 77 Phase 6)
 
@@ -155,6 +155,45 @@ final class RelayConfigurationLoaderTests: XCTestCase {
         }
     }
 
+    // MARK: - Priority Validation Tests
+    
+    func testAcceptsValidPriorityValues() throws {
+        let validPriorities = ["high", "medium", "low", "HIGH", "Medium", "LOW"]
+        
+        for priority in validPriorities {
+            let relay = AppleRelayConfig(type: "vsock-db", port: 5432, priority: priority)
+            let service = Service(image: "test:latest", x_apple_relays: [relay])
+            
+            // Should not throw
+            let loaded = try loader.loadRelays(from: [("test", service)])
+            XCTAssertEqual(loaded.count, 1, "Should load relay with priority: \(priority)")
+        }
+    }
+    
+    func testRejectsInvalidPriorityValues() {
+        let relay = AppleRelayConfig(type: "vsock-db", port: 5432, priority: "urgent")
+        let service = Service(image: "test:latest", x_apple_relays: [relay])
+        
+        XCTAssertThrowsError(try loader.loadRelays(from: [("test", service)])) { error in
+            guard let configError = error as? RelayConfigurationLoader.ConfigurationError,
+                  case .invalidPriority(let priority) = configError else {
+                XCTFail("Wrong error type")
+                return
+            }
+            XCTAssertEqual(priority, "urgent")
+        }
+    }
+    
+    func testAcceptsNilPriority() throws {
+        // Priority is optional
+        let relay = AppleRelayConfig(type: "vsock-db", port: 5432, priority: nil)
+        let service = Service(image: "test:latest", x_apple_relays: [relay])
+        
+        // Should not throw
+        let loaded = try loader.loadRelays(from: [("test", service)])
+        XCTAssertNil(loaded.first?.priority, "Priority should be nil")
+    }
+    
     // MARK: - Integration Tests
 
     func testLoadsHermesHonchoConfiguration() throws {

examples/README-vsock-relays.md

@@ -91,8 +91,38 @@ Container-Compose validates:
 - Port number is valid (1-65535)
 - No port conflicts across services
 - Required `target` field for MCP/log-stream types
+- Priority values (if provided) are `high`, `medium`, or `low`
 - Schema correctness before starting containers
 
+### Error Types
+
+Container-Compose throws specific errors that can be caught:
+
+```swift
+enum ConfigurationError: Error {
+    case unsupportedRelayType(String)   // Unknown relay type
+    case invalidPort(UInt32)              // Port 0 or > 65535
+    case missingTarget(String)           // MCP/log-stream missing target
+    case conflictingPort(UInt32, String) // Port already used
+    case invalidPriority(String)          // Priority not high/medium/low
+}
+```
+
+**Example error handling:**
+```swift
+do {
+    let relays = try loader.loadRelays(from: services)
+} catch let error as RelayConfigurationLoader.ConfigurationError {
+    switch error {
+    case .invalidPriority(let value):
+        print("Priority '\(value)' not supported. Use: high, medium, low")
+    case .missingTarget(let service):
+        print("Service '\(service)' requires target field")
+    // ... handle other errors
+    }
+}
+```
+
 ## Test Coverage
 
 - `RelayConfigurationLoaderTests.swift` - 23 tests