OPC # 0006: OPC Git Trunk-Based management

Co-authored-by: Copilot <copilot@github.com>

ControlPlane.Api/Endpoints/PromotionEndpoints.cs

@@ -1,5 +1,6 @@
 using ControlPlane.Api.Services;
 using ControlPlane.Core.Models;
+using ControlPlane.Core.Services;
 using System.Text.Json;
 
 namespace ControlPlane.Api.Endpoints;
@@ -178,6 +179,27 @@ public static class PromotionEndpoints
             }
         });
 
+        // GET /api/promotions/build-gate?sha={sha}
+        // Returns the build-gate status for the given commit SHA.
+        // If status is "Red", the promote button in the UI should be disabled.
+        g.MapGet("/build-gate", async (string sha, BuildHistoryService history, CancellationToken ct) =>
+        {
+            var builds = await history.GetBuildsByShaAsync(sha);
+            var latest = builds.MaxBy(b => b.StartedAt);
+            if (latest is null)
+                return Results.Ok(new { status = "Unknown", sha, buildId = (string?)null, buildStatus = (string?)null });
+
+            var gateStatus = latest.Status switch
+            {
+                BuildStatus.Succeeded => "Green",
+                BuildStatus.Failed    => "Red",
+                BuildStatus.Running   => "Running",
+                _                     => "Unknown",
+            };
+
+            return Results.Ok(new { status = gateStatus, sha, buildId = latest.Id, buildStatus = latest.Status.ToString() });
+        });
+
         return app;
     }
 }