fix(external-system-gateway): resolve ExternalSystemGateway-011 — name-keyed repository lookups replace fetch-all-then-filter on the call hot path

src/ScadaLink.SiteRuntime/Repositories/SiteExternalSystemRepository.cs

@@ -53,6 +53,31 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
         return all.FirstOrDefault(e => e.Id == id);
     }
 
+    /// <summary>
+    /// ExternalSystemGateway-011: genuine name-keyed lookup. The <c>external_systems</c>
+    /// table has <c>name</c> as its PRIMARY KEY, so this is a single indexed-row fetch
+    /// rather than the previous fetch-all-then-filter.
+    /// </summary>
+    public async Task<ExternalSystemDefinition?> GetExternalSystemByNameAsync(
+        string name, CancellationToken cancellationToken = default)
+    {
+        await using var connection = CreateConnection();
+        await connection.OpenAsync(cancellationToken);
+
+        await using var command = connection.CreateCommand();
+        command.CommandText = @"
+            SELECT name, endpoint_url, auth_type, auth_configuration
+            FROM external_systems
+            WHERE name = @name";
+        command.Parameters.AddWithValue("@name", name);
+
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        if (!await reader.ReadAsync(cancellationToken))
+            return null;
+
+        return MapExternalSystem(reader);
+    }
+
     // ── ExternalSystemMethod (read) ──
 
     public async Task<IReadOnlyList<ExternalSystemMethod>> GetMethodsByExternalSystemIdAsync(
@@ -80,6 +105,23 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
         return ParseMethodDefinitions(json, externalSystemId);
     }
 
+    /// <summary>
+    /// ExternalSystemGateway-011: name-keyed method lookup. The site store keeps a
+    /// system's methods in a single JSON column, so this fetches that one row and
+    /// matches the named method in memory. The parent system is resolved via
+    /// <see cref="GetMethodsByExternalSystemIdAsync"/>, which already performs a
+    /// single keyed read of the <c>method_definitions</c> column — this is no more
+    /// I/O than the gateway's previous fetch-all-methods-then-filter call, and on
+    /// the SQL-backed Central repository it is a genuine indexed query.
+    /// </summary>
+    public async Task<ExternalSystemMethod?> GetMethodByNameAsync(
+        int externalSystemId, string methodName, CancellationToken cancellationToken = default)
+    {
+        var methods = await GetMethodsByExternalSystemIdAsync(externalSystemId, cancellationToken);
+        return methods.FirstOrDefault(
+            m => m.Name.Equals(methodName, StringComparison.OrdinalIgnoreCase));
+    }
+
     public async Task<ExternalSystemMethod?> GetExternalSystemMethodByIdAsync(
         int id, CancellationToken cancellationToken = default)
     {
@@ -134,6 +176,38 @@ public class SiteExternalSystemRepository : IExternalSystemRepository
         return all.FirstOrDefault(d => d.Id == id);
     }
 
+    /// <summary>
+    /// ExternalSystemGateway-011: genuine name-keyed lookup. The
+    /// <c>database_connections</c> table has <c>name</c> as its PRIMARY KEY, so this
+    /// is a single indexed-row fetch rather than fetch-all-then-filter.
+    /// </summary>
+    public async Task<DatabaseConnectionDefinition?> GetDatabaseConnectionByNameAsync(
+        string name, CancellationToken cancellationToken = default)
+    {
+        await using var connection = CreateConnection();
+        await connection.OpenAsync(cancellationToken);
+
+        await using var command = connection.CreateCommand();
+        command.CommandText = @"
+            SELECT name, connection_string, max_retries, retry_delay_ms
+            FROM database_connections
+            WHERE name = @name";
+        command.Parameters.AddWithValue("@name", name);
+
+        await using var reader = await command.ExecuteReaderAsync(cancellationToken);
+        if (!await reader.ReadAsync(cancellationToken))
+            return null;
+
+        return new DatabaseConnectionDefinition(
+            name: reader.GetString(0),
+            connectionString: reader.GetString(1))
+        {
+            Id = GenerateSyntheticId(reader.GetString(0)),
+            MaxRetries = reader.GetInt32(2),
+            RetryDelay = TimeSpan.FromMilliseconds(reader.GetInt64(3))
+        };
+    }
+
     // ── Write operations (not supported on site) ──
 
     public Task AddExternalSystemAsync(ExternalSystemDefinition definition, CancellationToken cancellationToken = default)