[BUG] Azure Cosmos Java sdk not validating item ids

[vsarris]

Describe the bug
Azure Java SDK for Cosmos lacks proper validation when inserting rows into a container.
As we have verified in docs for allowed characters in an id, plus trying this hands on in the azure console, whenever we try to create one row with id including e.g. the '/' character we get this error: Illegal characters ['/', '\', '#'] cannot be used in Resource ID.
However, the java client allows these characters. If you try to process/delete them it's also not possible with the java client as it reaches a not found error. So this can lead to corrupted data inside a cosmos container(as we realized) instead of failing fast and not allowing those at all.

Exception or Stack Trace
Adding only the stacktrace for the deletion, as insertion is always successful.

Exception in thread "main" java.lang.IllegalArgumentException: Entity with the specified id does not exist in the system. More info: https://aka.ms/cosmosdb-tsg-not-found-java, - Path: /dbs/cdp-test-sessions-db/colls/active_sessions2/docs/clientKeyTest__386fd1c9-1bb0-403d-be24-10d4c0fae5db__kkia/en/
	at com.azure.cosmos.implementation.RxDocumentServiceRequest.<init>(RxDocumentServiceRequest.java:254)
	at com.azure.cosmos.implementation.RxDocumentServiceRequest.<init>(RxDocumentServiceRequest.java:274)
	at com.azure.cosmos.implementation.RxDocumentServiceRequest.<init>(RxDocumentServiceRequest.java:290)
	at com.azure.cosmos.implementation.RxDocumentServiceRequest.<init>(RxDocumentServiceRequest.java:319)
	at com.azure.cosmos.implementation.RxDocumentServiceRequest.create(RxDocumentServiceRequest.java:559)
	at com.azure.cosmos.implementation.RxDocumentClientImpl.deleteDocumentInternal(RxDocumentClientImpl.java:3733)
	at com.azure.cosmos.implementation.RxDocumentClientImpl.lambda$deleteDocumentCore$93(RxDocumentClientImpl.java:3704)
	at com.azure.cosmos.implementation.ObservableHelper.lambda$inlineIfPossibleAsObs$1(ObservableHelper.java:44)
	at com.azure.cosmos.implementation.BackoffRetryUtility.lambda$executeRetry$0(BackoffRetryUtility.java:36)
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:45)
	at reactor.core.publisher.FluxRetryWhen.subscribe(FluxRetryWhen.java:81)
	at reactor.core.publisher.MonoRetryWhen.subscribeOrReturn(MonoRetryWhen.java:46)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:63)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:165)
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2570)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.request(MonoFlatMap.java:194)
	at reactor.core.publisher.FluxDoOnEach$DoOnEachSubscriber.request(FluxDoOnEach.java:108)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.request(FluxContextWrite.java:136)
	at reactor.core.publisher.BlockingSingleSubscriber.onSubscribe(BlockingSingleSubscriber.java:54)
	at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onSubscribe(FluxContextWrite.java:101)
	at reactor.core.publisher.FluxDoOnEach$DoOnEachSubscriber.onSubscribe(FluxDoOnEach.java:121)
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onSubscribe(MonoFlatMap.java:117)
	at com.azure.cosmos.implementation.DiagnosticsProvider.subscribe(DiagnosticsProvider.java:1064)
	at com.azure.cosmos.implementation.DiagnosticsProvider.access$300(DiagnosticsProvider.java:76)
	at com.azure.cosmos.implementation.DiagnosticsProvider$PropagatingMono.subscribe(DiagnosticsProvider.java:1090)
	at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:76)
	at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:55)
	at reactor.core.publisher.Mono.subscribe(Mono.java:4576)
	at reactor.core.publisher.Mono.block(Mono.java:1778)
	at com.sitecore.cosmos.integration.ChangeFeedServiceSetup2Utils.main(ChangeFeedServiceSetup2Utils.java:114)
	Suppressed: java.lang.Exception: #block terminated with an error
		at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:104)
		at reactor.core.publisher.Mono.block(Mono.java:1779)
		... 1 more

To Reproduce
Insert with the java sdk an item in a container with an id like this:
clientKeyTest__386fd1c9-1bb0-403d-be24-10d4c0fae5db__kkia/en
You can see it will appear in the container successfully. Then you cannot view/delete this with the java client.
You cannot delete it through the azure console, you cannot delete it through azure console.

Code Snippet

    ObjectNode testDocument = objectMapper.createObjectNode();
    testDocument.put("id", "clientKeyTest__386fd1c9-1bb0-403d-be24-10d4c0fae5db__kkia/en");
    testDocument.put("shardId", 1);

CosmosAsyncClient cosmosClient = new CosmosClientBuilder()
        .endpoint(endpoint)
        .key(key)
        .consistencyLevel(ConsistencyLevel.SESSION)
        .contentResponseOnWriteEnabled(false)
        .gatewayMode(new GatewayConnectionConfig()
            .setMaxConnectionPoolSize(1000)
            .setIdleConnectionTimeout(Duration.ofSeconds(60)))
        .buildAsyncClient();
    CosmosAsyncDatabase sharedDb = cosmosClient.getDatabase(sharedDatabase);
    CosmosAsyncContainer container = sharedDb.getContainer(CONTAINER_NAME);

     container.createItem(testDocument, new PartitionKey(doc.get("shardId").asInt()),
            new CosmosItemRequestOptions()));

Expected behavior
If Azure Cosmos is disallowing illegal characters in ids the java client should return a validation error first place instead of allowing you to add such in the container and then having trouble processing and removing them.

Screenshots

Setup (please complete the following information):

• OS: Azure Linux 3.0
  AZURELINUX_BUILD_NUMBER=3.0.20251206
  DISTRIB_ID="azurelinux"

• IDE: IntelliJ

• Library/Libraries: implementation("com.azure:azure-cosmos:4.76.0")

• Java version: openjdk version "25.0.1" 2025-10-21 LTS
  OpenJDK Runtime Environment Microsoft-12574220 (build 25.0.1+8-LTS)

• App Server/Environment: [e.g. Tomcat, WildFly, Azure Function, Apache Spark, Databricks, IDE plugin or anything special]

• Frameworks: Micronaut

Additional context
Add any other context about the problem here.

Information Checklist
Kindly make sure that you have added all the following information above and checkoff the required fields otherwise we will treat the issuer as an incomplete report

• Bug Description Added
• Repro Steps Added
• Setup information Added

[github-actions]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @kushagraThapar @pjohari-ms @TheovanKraay.

[samvaity]

@kushagraThapar Believe this needs to be fixed on the SDK side to not allow illegal characters in ids ?