fix(auditlog): evolve existing site auditlog.db schema for ExecutionId

src/ScadaLink.AuditLog/Site/SqliteAuditWriter.cs

@@ -121,6 +121,46 @@ public class SqliteAuditWriter : IAuditWriter, ISiteAuditQueue, IAsyncDisposable
                 ON AuditLog (ForwardState, OccurredAtUtc);
             """;
         cmd.ExecuteNonQuery();
+
+        // Audit Log #23 (ExecutionId): additively add the ExecutionId column.
+        // CREATE TABLE IF NOT EXISTS above does NOT add columns to an AuditLog
+        // table that already exists from a pre-ExecutionId build, so an
+        // auditlog.db created by an older build needs the column ALTER-ed in.
+        // The file is durable across restart/failover by design (7-day
+        // retention), so without this step every WriteAsync on an upgraded
+        // deployment would bind $ExecutionId against a missing column and the
+        // best-effort write path would silently drop every site audit row.
+        // SQLite has no "ADD COLUMN IF NOT EXISTS"; the column presence is
+        // probed first and the ALTER skipped when already there. The column is
+        // nullable with no default, so any row written before this migration
+        // reads back ExecutionId = null (back-compat).
+        AddColumnIfMissing("ExecutionId", "TEXT NULL");
+    }
+
+    /// <summary>
+    /// Audit Log #23 (ExecutionId): adds a column to <c>AuditLog</c> only when
+    /// it is not already present. SQLite lacks <c>ADD COLUMN IF NOT EXISTS</c>,
+    /// so the schema is probed via <c>PRAGMA table_info</c> first. Idempotent —
+    /// safe to run on every <see cref="InitializeSchema"/>. Mirrors
+    /// <c>StoreAndForwardStorage.AddColumnIfMissingAsync</c>; kept synchronous
+    /// here to match the rest of this writer's bootstrap DDL.
+    /// </summary>
+    private void AddColumnIfMissing(string columnName, string columnDefinition)
+    {
+        using var probe = _connection.CreateCommand();
+        probe.CommandText = "SELECT COUNT(*) FROM pragma_table_info('AuditLog') WHERE name = $name";
+        probe.Parameters.AddWithValue("$name", columnName);
+        var exists = Convert.ToInt32(probe.ExecuteScalar()) > 0;
+        if (exists)
+        {
+            return;
+        }
+
+        using var alter = _connection.CreateCommand();
+        // Column name + definition are caller-controlled constants, never user
+        // input — safe to interpolate (parameters are not permitted in DDL).
+        alter.CommandText = $"ALTER TABLE AuditLog ADD COLUMN {columnName} {columnDefinition}";
+        alter.ExecuteNonQuery();
     }
 
     /// <summary>