From c4149af23a32410d4ae8b63cd51a65feb0cf8562 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Ren=C3=A9=20White=20Enciso?=
 <jrenewhite@gmail.com>
Date: Wed, 25 Feb 2026 13:13:56 -0600
Subject: [PATCH] feat(furniture-domain): enforce availability decision
 invariants

---
 docs/migration/behavior-invariants.md         |  2 +
 .../FurnitureAvailabilityDecisionService.cs   | 11 +++++-
 ...rnitureAvailabilityDecisionServiceTests.cs | 38 +++++++++++++++++++
 3 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/docs/migration/behavior-invariants.md b/docs/migration/behavior-invariants.md
index 0233310..ba3889c 100644
--- a/docs/migration/behavior-invariants.md
+++ b/docs/migration/behavior-invariants.md
@@ -4,6 +4,8 @@
 - Availability decision outcome remains unchanged for equivalent inputs.
 - Correlation propagation behavior remains unchanged.
 - Transport contracts stay stable at service boundary.
+- Missing display names map to `Unknown Furniture`.
+- Negative inventory quantities are clamped to `0`.
 
 ## Validation Approach
 - Compare pre/post extraction contract examples.
diff --git a/src/Furniture.Domain/Decisions/FurnitureAvailabilityDecisionService.cs b/src/Furniture.Domain/Decisions/FurnitureAvailabilityDecisionService.cs
index c2337ef..c9a9a24 100644
--- a/src/Furniture.Domain/Decisions/FurnitureAvailabilityDecisionService.cs
+++ b/src/Furniture.Domain/Decisions/FurnitureAvailabilityDecisionService.cs
@@ -38,10 +38,17 @@ public sealed class FurnitureAvailabilityDecisionService : IFurnitureAvailabilit
         ProductContractResponse catalogResponse,
         InventoryItemLookupResponse inventoryResponse)
     {
+        var displayName = string.IsNullOrWhiteSpace(catalogResponse.DisplayName)
+            ? "Unknown Furniture"
+            : catalogResponse.DisplayName;
+        var quantityAvailable = inventoryResponse.QuantityAvailable < 0
+            ? 0
+            : inventoryResponse.QuantityAvailable;
+
         return new FurnitureAvailabilityDecisionResponse(
             request.FurnitureId,
-            catalogResponse.DisplayName,
-            inventoryResponse.QuantityAvailable);
+            displayName,
+            quantityAvailable);
     }
 
     private static string ResolveCorrelationId(string correlationId)
diff --git a/tests/Furniture.Domain.UnitTests/FurnitureAvailabilityDecisionServiceTests.cs b/tests/Furniture.Domain.UnitTests/FurnitureAvailabilityDecisionServiceTests.cs
index 67c3b20..3dbc098 100644
--- a/tests/Furniture.Domain.UnitTests/FurnitureAvailabilityDecisionServiceTests.cs
+++ b/tests/Furniture.Domain.UnitTests/FurnitureAvailabilityDecisionServiceTests.cs
@@ -51,4 +51,42 @@ public class FurnitureAvailabilityDecisionServiceTests
         Assert.Equal("Chair", response.DisplayName);
         Assert.Equal(12, response.QuantityAvailable);
     }
+
+    [Fact]
+    public void ComposeResponse_WhenCatalogDisplayNameMissing_UsesFallbackName()
+    {
+        var service = new FurnitureAvailabilityDecisionService();
+        var request = new FurnitureAvailabilityDecisionRequest("FUR-004", "corr-004");
+        var catalog = new ProductContractResponse(
+            new CatalogContractEnvelope("1.0.0", "corr-004"),
+            "FUR-004",
+            string.Empty);
+        var inventory = new InventoryItemLookupResponse(
+            new InventoryContractEnvelope("1.0.0", "corr-004"),
+            "FUR-004",
+            5);
+
+        var response = service.ComposeResponse(request, catalog, inventory);
+
+        Assert.Equal("Unknown Furniture", response.DisplayName);
+    }
+
+    [Fact]
+    public void ComposeResponse_WhenInventoryNegative_ClampsQuantityToZero()
+    {
+        var service = new FurnitureAvailabilityDecisionService();
+        var request = new FurnitureAvailabilityDecisionRequest("FUR-005", "corr-005");
+        var catalog = new ProductContractResponse(
+            new CatalogContractEnvelope("1.0.0", "corr-005"),
+            "FUR-005",
+            "Shelf");
+        var inventory = new InventoryItemLookupResponse(
+            new InventoryContractEnvelope("1.0.0", "corr-005"),
+            "FUR-005",
+            -3);
+
+        var response = service.ComposeResponse(request, catalog, inventory);
+
+        Assert.Equal(0, response.QuantityAvailable);
+    }
 }