fix(db): register legacy task migrations

backend-tests/MigrationSnapshotTests.cs

@@ -1,3 +1,7 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Nexus.Api.Data;
 using Nexus.Api.Migrations;
 using Xunit;
 
@@ -5,6 +9,21 @@ namespace Nexus.Api.Tests;
 
 public sealed class MigrationSnapshotTests
 {
+    [Fact]
+    public void Historical_task_migrations_are_discoverable()
+    {
+        var options = new DbContextOptionsBuilder<NexusDbContext>()
+            .UseNpgsql(
+                "Host=127.0.0.1;Database=nexus_migration_contract;Username=nexus;Password=unused")
+            .Options;
+        using var db = new NexusDbContext(options);
+        var migrations = db.GetService<IMigrationsAssembly>().Migrations.Keys;
+
+        Assert.Contains("20260618233000_AddTaskParentChild", migrations);
+        Assert.Contains("20260618233001_AddTaskDueDate", migrations);
+        Assert.Contains("20260618233002_AddActivityTaskReference", migrations);
+    }
+
     [Fact]
     public void Snapshot_builds_agent_provisioning_relationships()
     {

backend-tests/ToxiproxyAgentProvisioningIntegrationTests.cs

@@ -140,7 +140,14 @@ public sealed class ToxiproxyAgentProvisioningIntegrationTests
 
         var reconciled = await service.GetByIdAsync(created.Proposal.Id);
         Assert.NotNull(reconciled);
-        Assert.Equal(AgentProposalStates.Ready, reconciled!.Status);
+        Assert.True(
+            string.Equals(
+                AgentProposalStates.Ready,
+                reconciled!.Status,
+                StringComparison.Ordinal),
+            $"Expected ready after read-only reconciliation, got "
+            + $"'{reconciled.Status}' ({reconciled.Error?.Code}: "
+            + $"{reconciled.Error?.Message}).");
         Assert.Equal("release-analyst", reconciled.OpenClawAgentId);
         Assert.Equal(1, gateway.CreateCalls);
     }