Worked on the Azure/azure-sdk-for-python repository to address a critical bug in session-token generation within the Cosmos Python SDK. Focused on backend development using Python and the Azure Cosmos DB SDK, the work involved resolving a KeyError caused by missing 'version' fields in partition key definitions by defaulting the version to 1. This fix restored session-consistency cache hits and ensured reliable session reads. Comprehensive unit and regression tests were implemented to validate correct token generation and effective partition key calculation, including distinct handling for V1 and V2 EPKs. Updates to the test harness and changelog further strengthened code reliability.