feat(engine): ConnectionInstanceRegistry with per-id caching + invalidate on delete

src/VolcanicCore.Api/Endpoints/ConnectionsEndpoints.cs

@@ -1,6 +1,7 @@
 using System.Text.Json;
 using VolcanicCore.Api.Auth;
 using VolcanicCore.Api.Contracts;
+using VolcanicCore.Api.Engine;
 using VolcanicCore.Persistence.Repositories;
 
 namespace VolcanicCore.Api.Endpoints;
@@ -46,8 +47,11 @@ public static class ConnectionsEndpoints
             }
         });
 
-        g.MapDelete("/{id}", (string id, ConnectionRepository repo) =>
-            repo.Delete(id) ? Results.NoContent() : Results.NotFound());
+        g.MapDelete("/{id}", async (string id, ConnectionRepository repo, ConnectionInstanceRegistry instances) =>
+        {
+            await instances.InvalidateAsync(id);
+            return repo.Delete(id) ? Results.NoContent() : Results.NotFound();
+        });
     }
 
     private static JsonElement StripSecrets(string configJson, IReadOnlySet<string> secretFields)

src/VolcanicCore.Api/Engine/ConnectionInstanceRegistry.cs

@@ -0,0 +1,69 @@
+using System.Text.Json;
+using VolcanicCore.Api.Registries;
+using VolcanicCore.Persistence.Repositories;
+
+namespace VolcanicCore.Api.Engine;
+
+public sealed class ConnectionInstanceRegistry : IConnectionInstanceRegistry, IAsyncDisposable
+{
+    private sealed record Entry(string ProviderId, object Handle);
+
+    private readonly ConnectionRepository _repo;
+    private readonly ConnectionProviderRegistry _providers;
+    private readonly Dictionary<string, Entry> _cache = new(StringComparer.Ordinal);
+    private readonly SemaphoreSlim _mu = new(1, 1);
+
+    public ConnectionInstanceRegistry(ConnectionRepository repo, ConnectionProviderRegistry providers)
+    {
+        _repo = repo;
+        _providers = providers;
+    }
+
+    public async Task<object> GetAsync(string connectionId, CancellationToken ct)
+    {
+        await _mu.WaitAsync(ct);
+        try
+        {
+            if (_cache.TryGetValue(connectionId, out var hit)) return hit.Handle;
+
+            var row = _repo.Get(connectionId)
+                ?? throw new KeyNotFoundException($"Connection {connectionId} not found.");
+            var provider = _providers.Get(row.ProviderId);
+            using var doc = JsonDocument.Parse(row.ConfigJson);
+            var handle = await provider.OpenAsync(doc.RootElement.Clone(), ct);
+            _cache[connectionId] = new Entry(row.ProviderId, handle);
+            return handle;
+        }
+        finally { _mu.Release(); }
+    }
+
+    public async Task InvalidateAsync(string connectionId)
+    {
+        await _mu.WaitAsync();
+        Entry? removed = null;
+        try
+        {
+            if (_cache.Remove(connectionId, out var e)) removed = e;
+        }
+        finally { _mu.Release(); }
+
+        if (removed is not null)
+            await _providers.Get(removed.ProviderId).CloseAsync(removed.Handle);
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        Entry[] snapshot;
+        await _mu.WaitAsync();
+        try
+        {
+            snapshot = _cache.Values.ToArray();
+            _cache.Clear();
+        }
+        finally { _mu.Release(); }
+
+        foreach (var e in snapshot)
+            try { await _providers.Get(e.ProviderId).CloseAsync(e.Handle); }
+            catch { /* best-effort on shutdown */ }
+    }
+}

src/VolcanicCore.Api/Program.cs

@@ -2,6 +2,7 @@ using Microsoft.AspNetCore.Authentication.Cookies;
 using VolcanicCore.Api;
 using VolcanicCore.Api.Auth;
 using VolcanicCore.Api.Endpoints;
+using VolcanicCore.Api.Engine;
 using VolcanicCore.Api.Registries;
 using VolcanicCore.Core;
 using VolcanicCore.Persistence;
@@ -112,6 +113,10 @@ builder.Services.AddSingleton<NodeRegistry>(sp =>
 builder.Services.AddSingleton<ConnectionProviderRegistry>(sp =>
     new ConnectionProviderRegistry(sp.GetServices<IConnectionProvider>()));
 
+builder.Services.AddSingleton<ConnectionInstanceRegistry>();
+builder.Services.AddSingleton<IConnectionInstanceRegistry>(sp =>
+    sp.GetRequiredService<ConnectionInstanceRegistry>());
+
 var app = builder.Build();
 
 // Apply migrations at boot.