PartitionKey: Fixes latent issues in ContainerPropertiesExtensions and hardens InitTaskThreadSafe

Addresses PR Deep Reviewer findings surfaced while addressing Fabian's feedback:

- GetItemIdFromStreamIfRequiredAsync: guards against ResolveByNameAsync returning a null ContainerProperties, matching the null guard already present in EnsureIdGetAppendedToPartitionKeyIfNeededAsync. Prevents an NRE on containerProperties.IsLastPartitionKeyPathId when the collection cache returns null.

- Both helpers now rethrow OperationCanceledException instead of swallowing it in the blanket catch, so caller-cancelled tokens propagate as expected.

- InitTaskThreadSafe: also resets metadataCallCount between iterations for hygiene (previously relied on VmMetadataApiHandler's static latch) and uses Interlocked.Exchange for counter resets to stay consistent with the increment side. Adds a comment explaining why the URI bag is drained in place rather than reassigned.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: NaluTripician

Microsoft.Azure.Cosmos/src/Resource/Settings/ContainerPropertiesExtensions.cs

@@ -38,6 +38,10 @@ internal static class ContainerPropertiesExtensions
                     trace: NoOpTrace.Singleton,
                     cancellationToken: cancellationToken);
             }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
             catch (Exception)
             {
                 // Container may not exist yet (e.g. operations on non-existent containers).
@@ -115,14 +119,18 @@ internal static class ContainerPropertiesExtensions
                     trace: NoOpTrace.Singleton,
                     cancellationToken: cancellationToken);
             }
+            catch (OperationCanceledException)
+            {
+                throw;
+            }
             catch (Exception)
             {
                 // Container may not exist yet (e.g. operations on non-existent containers).
                 // Swallow the exception and let the actual operation surface the proper error.
                 return (itemId, streamPayload);
             }
 
-            if (containerProperties.IsLastPartitionKeyPathId)
+            if (containerProperties != null && containerProperties.IsLastPartitionKeyPathId)
             {
                 return await ContainerPropertiesExtensions.GetIdFromStreamPayloadAsync(streamPayload);
             }

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/ClientTests.cs

@@ -157,11 +157,14 @@ public async Task InitTaskThreadSafe()
                     httpCallCount,
                     $"Only the first task should do the http call. All other should wait on the first task. Observed URIs: [{string.Join(", ", httpRequestUris)}]");
 
-                // Reset counters and retry the client to verify a new http call is done for new requests
+                // Reset counters and retry the client to verify a new http call is done for new requests.
                 tasks.Clear();
                 delayCallBack = true;
                 this.TaskStartedCount = 0;
-                httpCallCount = 0;
+                Interlocked.Exchange(ref httpCallCount, 0);
+                Interlocked.Exchange(ref metadataCallCount, 0);
+                // Drain in-place: the RequestCallBack closure captured this specific bag instance,
+                // so we cannot swap the reference without the handler writing into a stale bag.
                 while (httpRequestUris.TryTake(out _))
                 {
                 }