fix: correct error message for full label length validation

Fix incorrect error message in NetworkConfiguration label validation.
The error previously stated "key length is greater than" when actually
checking the full label length (key=value combination).

Changes:
- Update error message to say "full label length (key=value)" instead of "key length"
- Add test case to verify the error message is correct

This makes the error message more accurate and helpful for users debugging
label validation issues.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: hobostay

Sources/ContainerResource/Network/NetworkConfiguration.swift

@@ -120,7 +120,7 @@ public struct NetworkConfiguration: Codable, Sendable, Identifiable {
 
         let fullLabel = "\(key)=\(value)"
         guard fullLabel.count <= labelLengthMax else {
-            throw ContainerizationError(.invalidArgument, message: "invalid label, key length is greater than \(labelLengthMax): \(fullLabel)")
+            throw ContainerizationError(.invalidArgument, message: "invalid label, full label length (key=value) is greater than \(labelLengthMax): \(fullLabel)")
         }
     }
 }

Tests/ContainerResourceTests/NetworkConfigurationTest.swift

@@ -102,4 +102,22 @@ struct NetworkConfigurationTest {
         }
     }
 
+    @Test func testFullLabelLengthErrorMessage() throws {
+        // Test that the error message correctly mentions "full label length" instead of "key length"
+        let id = "foo"
+        let ipv4Subnet = try CIDRv4("192.168.64.1/24")
+        // Create a label where the full label (key=value) exceeds 4096 chars
+        let labels = ["test-key": String(repeating: "x", count: 4097 - "test-key=".count)]
+
+        #expect {
+            _ = try NetworkConfiguration(id: id, mode: .nat, ipv4Subnet: ipv4Subnet, labels: labels)
+        } throws: { error in
+            guard let err = error as? ContainerizationError else { return false }
+            #expect(err.code == .invalidArgument)
+            // Verify the error message mentions "full label length" not just "key length"
+            #expect(err.message.contains("full label length"))
+            return true
+        }
+    }
+
 }