perf(audit-log): bound GetExecutionTreeAsync edge scan to a root-anchored time window (partition elimination)

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/AuditLogRepository.cs

@@ -665,6 +665,16 @@ VALUES
     // practice.
     private const int ExecutionChainMaxDepth = 32;
 
+    // Execution trees span minutes, not years — an inbound request and every script it
+    // spawns all fire inside one operational burst. Anchoring the Edges CTE scan to a
+    // narrow window around the root's first event lets SQL Server eliminate every
+    // AuditLog partition outside it, turning a full-table DISTINCT scan into a seek on
+    // IX_AuditLog_Execution over one or two months (arch-review 04, P2). The slack absorbs
+    // minor clock skew before the root; the max span is the documented traversal bound —
+    // a genuine descendant stamped beyond it is excluded by design.
+    private static readonly TimeSpan ExecutionTreeWindowSlack = TimeSpan.FromHours(1);
+    private static readonly TimeSpan ExecutionTreeMaxSpan = TimeSpan.FromDays(7);
+
     /// <inheritdoc />
     public async Task<IReadOnlyList<ExecutionTreeNode>> GetExecutionTreeAsync(
         Guid executionId,
@@ -713,6 +723,31 @@ VALUES
                 rootExecutionId = parent.Value;
             }
 
+            // --- Between phases: bound the down-walk to a root-anchored window ---
+            // The root's first event timestamp anchors a [rootFirst - slack, rootFirst + maxSpan)
+            // window used to prune the Edges CTE scan to a handful of partitions. A row-less stub
+            // root (purged/no-action parent) has no MIN — leave the scan unbounded in that
+            // degenerate case (correctness over speed).
+            DateTime? rootFirstOccurred;
+            await using (var winCmd = conn.CreateCommand())
+            {
+                winCmd.CommandText =
+                    "SELECT MIN(OccurredAtUtc) FROM dbo.AuditLog WHERE ExecutionId = @root;";
+                var pWinRoot = winCmd.CreateParameter();
+                pWinRoot.ParameterName = "@root";
+                pWinRoot.Value = rootExecutionId;
+                winCmd.Parameters.Add(pWinRoot);
+
+                var winResult = await winCmd.ExecuteScalarAsync(ct).ConfigureAwait(false);
+                rootFirstOccurred = winResult is null or DBNull ? null : (DateTime)winResult;
+            }
+
+            // Build the optional window predicate for the Edges CTE. When the root has rows the
+            // scan is confined to the window (partition elimination); otherwise it stays unbounded.
+            var edgesWindowPredicate = rootFirstOccurred is null
+                ? string.Empty
+                : "AND OccurredAtUtc >= @winStart AND OccurredAtUtc < @winEnd";
+
             // --- Phase 2: walk down from the root via a recursive CTE ---------
             // Edges : a non-recursive, DISTINCT (ExecutionId, ParentExecutionId)
             //         edge set distilled from AuditLog. Recursing over edges
@@ -743,6 +778,7 @@ VALUES
                         SELECT DISTINCT ExecutionId, ParentExecutionId
                         FROM dbo.AuditLog
                         WHERE ExecutionId IS NOT NULL
+                        {edgesWindowPredicate}
                     ),
                     Chain AS (
                         -- Anchor: the root execution id, seeded as a literal so
@@ -797,6 +833,19 @@ VALUES
                 pRoot.Value = rootExecutionId;
                 downCmd.Parameters.Add(pRoot);
 
+                if (rootFirstOccurred is { } rootFirst)
+                {
+                    var pWinStart = downCmd.CreateParameter();
+                    pWinStart.ParameterName = "@winStart";
+                    pWinStart.Value = rootFirst - ExecutionTreeWindowSlack;
+                    downCmd.Parameters.Add(pWinStart);
+
+                    var pWinEnd = downCmd.CreateParameter();
+                    pWinEnd.ParameterName = "@winEnd";
+                    pWinEnd.Value = rootFirst + ExecutionTreeMaxSpan;
+                    downCmd.Parameters.Add(pWinEnd);
+                }
+
                 await using var reader = await downCmd.ExecuteReaderAsync(ct).ConfigureAwait(false);
                 while (await reader.ReadAsync(ct).ConfigureAwait(false))
                 {