feat(stability): unify readiness and recovery

backend/Controllers/AgentsController.cs

@@ -5,6 +5,7 @@ using System.Diagnostics;
 using System.Security.Claims;
 using Nexus.Api.DTOs;
 using Nexus.Api.Integrations;
+using Nexus.Api.Http;
 using Nexus.Api.Repositories;
 using Nexus.Api.Services;
 
@@ -160,9 +161,15 @@ public class AgentsController(
     public async Task<IResult> SaveConfigFile(string id, string fileName, [FromBody] SaveConfigRequest request, CancellationToken ct)
     {
         if (request.Content is null)
-            return Results.BadRequest(new { error = "Content is required." });
+            return Results.ValidationProblem(new Dictionary<string, string[]>
+            {
+                ["content"] = ["Content is required."]
+            });
         if (string.IsNullOrWhiteSpace(request.ExpectedHash))
-            return Results.BadRequest(new { error = "ExpectedHash is required." });
+            return Results.ValidationProblem(new Dictionary<string, string[]>
+            {
+                ["expectedHash"] = ["ExpectedHash is required."]
+            });
 
         try
         {
@@ -170,7 +177,10 @@ public class AgentsController(
             var idempotencyKey = Request.Headers["Idempotency-Key"].FirstOrDefault()?.Trim();
             if (string.IsNullOrWhiteSpace(idempotencyKey))
             {
-                return Results.BadRequest(new { error = "Idempotency-Key header is required." });
+                return Results.ValidationProblem(new Dictionary<string, string[]>
+                {
+                    ["Idempotency-Key"] = ["Idempotency-Key header is required."]
+                });
             }
 
             var invocation = OpenClawInvocationContext.Create(
@@ -204,15 +214,15 @@ public class AgentsController(
         }
         catch (OpenClawAgentConfigurationConflictException ex)
         {
-            return Results.Json(
-                new
+            return NexusHttpResults.Problem(
+                StatusCodes.Status409Conflict,
+                ex.Message,
+                NexusProblemCodes.Conflict,
+                extensions: new Dictionary<string, object?>
                 {
-                    code = ex.Code,
-                    message = ex.Message,
-                    ex.ExpectedHash,
-                    ex.CurrentHash
-                },
-                statusCode: StatusCodes.Status409Conflict);
+                    ["expectedHash"] = ex.ExpectedHash,
+                    ["currentHash"] = ex.CurrentHash
+                });
         }
         catch (OpenClawAgentConfigurationValidationException ex)
         {