Extract TelemetryHelper for shared telemetry logic\n\nTask ID: task-2.1-extract-telemetry-helper

.gitignore

@@ -292,3 +292,6 @@ generated_task_specs.json
 
 # Git worktrees
 .worktrees/
+
+# Demo directory (local only)
+demo/

csharp/doc/telemetry-design.md

@@ -2846,3 +2846,83 @@ This **direct object telemetry design (V3)** provides a simple approach to colle
 4. **Deterministic emission**: Exactly one telemetry event per statement — on reader dispose (success) or catch block (error)
 5. **Flush-before-close**: Connection dispose blocks until all pending telemetry is sent to Databricks
 6. **JDBC-compatible**: snake_case JSON field names, same proto schema, same export endpoint
+
+---
+
+## Implementation Notes - E2E Test Infrastructure (2026-03-13)
+
+### Files Implemented
+
+1. **CapturingTelemetryExporter.cs** (`csharp/test/E2E/Telemetry/CapturingTelemetryExporter.cs`)
+   - Thread-safe telemetry event capture using `ConcurrentBag<TelemetryFrontendLog>`
+   - Export call counting for validation
+   - Reset capability for test cleanup
+
+2. **TelemetryTestHelpers.cs** (`csharp/test/E2E/Telemetry/TelemetryTestHelpers.cs`)
+   - `CreateConnectionWithCapturingTelemetry()` - Uses `TelemetryClientManager.ExporterOverride` to inject test exporter
+   - `WaitForTelemetryEvents()` - Waits for expected telemetry events with timeout
+   - Proto field assertion helpers for session, system config, connection params, SQL operations, and errors
+
+3. **TelemetryBaselineTests.cs** (`csharp/test/E2E/Telemetry/TelemetryBaselineTests.cs`)
+   - 10 baseline E2E tests validating all currently populated proto fields
+   - Tests against real Databricks workspace (no backend connectivity required)
+   - All tests passing ✅
+
+### Test Coverage
+
+Baseline tests validate:
+- ✅ session_id population
+- ✅ sql_statement_id population
+- ✅ operation_latency_ms > 0
+- ✅ system_configuration fields (driver_version, driver_name, os_name, runtime_name)
+- ✅ driver_connection_params.mode is set
+- ✅ sql_operation fields (statement_type, operation_type, result_latency)
+- ✅ Multiple statements share session_id but have unique statement_ids
+- ✅ Telemetry disabled when telemetry.enabled=false
+- ✅ error_info populated on SQL errors
+- ✅ UPDATE statement telemetry
+
+### Implementation Patterns Discovered
+
+1. **Exporter Override**: `TelemetryClientManager.ExporterOverride` provides global test exporter injection
+2. **Proto Enums**: Use nested structure `Statement.Types.Type.Query`, `Operation.Types.Type.ExecuteStatement`, etc.
+3. **Name Collision**: Proto `Statement` conflicts with `AdbcStatement` - resolved with type aliases:
+   ```csharp
+   using ProtoStatement = AdbcDrivers.Databricks.Telemetry.Proto.Statement;
+   using ProtoOperation = AdbcDrivers.Databricks.Telemetry.Proto.Operation;
+   using ProtoDriverMode = AdbcDrivers.Databricks.Telemetry.Proto.DriverMode;
+   ```
+4. **QueryResult**: `ExecuteQuery()` returns `QueryResult` with `Stream` property (IDisposable)
+
+### Test Pattern
+
+```csharp
+CapturingTelemetryExporter exporter = null!;
+AdbcConnection? connection = null;
+
+try
+{
+    var properties = TestEnvironment.GetDriverParameters(TestConfiguration);
+    (connection, exporter) = TelemetryTestHelpers.CreateConnectionWithCapturingTelemetry(properties);
+
+    // Execute operation
+    using var statement = connection.CreateStatement();
+    statement.SqlQuery = "SELECT 1";
+    var result = statement.ExecuteQuery();
+    using var reader = result.Stream;
+
+    statement.Dispose();
+
+    // Wait for and validate telemetry
+    var logs = await TelemetryTestHelpers.WaitForTelemetryEvents(exporter, expectedCount: 1);
+    var protoLog = TelemetryTestHelpers.GetProtoLog(logs[0]);
+
+    Assert.False(string.IsNullOrEmpty(protoLog.SessionId));
+    // ... more assertions
+}
+finally
+{
+    connection?.Dispose();
+    TelemetryTestHelpers.ClearExporterOverride();
+}
+```