feat: complete Nexus mission-control workflows

backend/Repositories/ActivityRepository.cs

@@ -3,7 +3,7 @@ using Nexus.Api.Data;
 
 namespace Nexus.Api.Repositories;
 
-public sealed class ActivityRepository(NexusDbContext db) : IActivityRepository
+public sealed class ActivityRepository(NexusDbContext db, Nexus.Api.Services.ILiveUpdateService liveUpdates) : IActivityRepository
 {
     public Task<List<ActivityEvent>> GetRecentAsync(int take, CancellationToken ct = default)
         => db.Activity.AsNoTracking().OrderByDescending(x => x.CreatedAt).Take(take).ToListAsync(ct);
@@ -39,17 +39,35 @@ public sealed class ActivityRepository(NexusDbContext db) : IActivityRepository
         return (items, totalCount);
     }
 
-    public Task<List<ActivityEvent>> GetByAgentAsync(string agentId, int take, CancellationToken ct = default)
-        => db.Activity.AsNoTracking()
-            .Where(x => x.Message.Contains(agentId, StringComparison.OrdinalIgnoreCase) || x.Type == "agent")
+    public async Task<List<ActivityEvent>> GetByAgentAsync(string agentId, int take, CancellationToken ct = default)
+    {
+        var candidateCount = Math.Max(take * 8, 100);
+        var recent = await db.Activity.AsNoTracking()
             .OrderByDescending(x => x.CreatedAt)
-            .Take(take)
+            .Take(candidateCount)
             .ToListAsync(ct);
 
+        return recent
+            .Where(x => Nexus.Api.Services.AgentActivityText.MatchesAgent(x.Message, agentId))
+            .Take(take)
+            .ToList();
+    }
+
     public async Task<ActivityEvent> AddAsync(ActivityEvent activity, CancellationToken ct = default)
     {
+        var agentIds = Nexus.Api.Services.AgentActivityText.ExtractAgentIds(activity.Message);
+        activity.Message = Nexus.Api.Services.AgentActivityText.RedactForDisplay(activity.Message);
         db.Activity.Add(activity);
         await db.SaveChangesAsync(ct);
+        liveUpdates.Publish("activity.created", new
+        {
+            activity.Id,
+            activity.Type,
+            activity.Message,
+            activity.TaskId,
+            activity.CreatedAt,
+            agentIds
+        }, "activity");
         return activity;
     }
 }