fix duraton in session list

src/Agent/AutopilotMonitor.Agent/buildcounter.txt

@@ -1 +1 @@
-119
+121

src/Backend/AutopilotMonitor.Functions/Services/TableStorageService.Sessions.cs

@@ -419,9 +419,13 @@ namespace AutopilotMonitor.Functions.Services
                         // Store accurate DurationSeconds based on first event timestamp (not registration StartedAt)
                         // The agent registers before events arrive, so registration StartedAt is always earlier
                         // than the actual enrollment start — using the first event gives the true enrollment duration.
-                        var durationStart = earliestEventTimestamp ?? currentStartedAt;
-                        if (durationStart < effectiveCompletedAt)
-                            update["DurationSeconds"] = (int)(effectiveCompletedAt - durationStart).TotalSeconds;
+                        // Use the effective StartedAt (already corrected by earlier batches via the StartedAt
+                        // alignment above), taking the minimum with the current batch's earliest timestamp.
+                        var effectiveStartedAt = earliestEventTimestamp.HasValue && earliestEventTimestamp.Value < currentStartedAt
+                            ? earliestEventTimestamp.Value
+                            : currentStartedAt;
+                        if (effectiveStartedAt < effectiveCompletedAt)
+                            update["DurationSeconds"] = (int)(effectiveCompletedAt - effectiveStartedAt).TotalSeconds;
                     }
 
                     // Track the most recent event timestamp for excessive data sender detection
@@ -704,10 +708,15 @@ namespace AutopilotMonitor.Functions.Services
                 Status = status,
                 FailureReason = entity.GetString("FailureReason") ?? string.Empty,
                 EventCount = SafeGetInt32(entity, "EventCount") ?? 0,
-                DurationSeconds = SafeGetInt32(entity, "DurationSeconds")
-                    ?? (completedAt.HasValue
+                DurationSeconds = SafeGetInt32(entity, "DurationSeconds") switch
+                {
+                    // Stored duration is valid — use it directly
+                    int d when d > 0 => d,
+                    // Duration missing or zero (bug from batch-split race) — recompute from timestamps
+                    _ => completedAt.HasValue
                         ? (int)(completedAt.Value - startedAt).TotalSeconds
-                        : (int)(DateTime.UtcNow - startedAt).TotalSeconds),
+                        : (int)(DateTime.UtcNow - startedAt).TotalSeconds
+                },
                 EnrollmentType = entity.GetString("EnrollmentType") ?? "v1",
                 DiagnosticsBlobName = entity.GetString("DiagnosticsBlobName"),
                 LastEventAt = SafeGetDateTime(entity, "LastEventAt"),