Source MSSQL fails migrating empty legacy stream state when first records arrive

A Slack thread reported a Source MSSQL edge case where streams that were empty during migration from the legacy MSSQL connector retained legacy stream state and later failed when the first records arrived. Slack context: https://app.slack.com/client/T02TET08MDH/C0B6NTCHFPW Requested by: Rodi (rodi@airbyte.io) Note: Customer/workspace/connection identifiers are intentionally omitted because this is a public issue. ### Issue category Confirmed connector bug, likely minor severity because the affected connection was unblocked by refreshing the streams, but the connector should handle this state migration path automatically. ### What happened - A connection was migrated from the legacy MSSQL source connector to the new MSSQL source connector. - Two selected tables were empty at migration time. - Because the tables were empty, their per-stream state apparently did not migrate and remained on legacy state with `"version": 2`. - On May 26, both previously-empty streams received a single row. - The next sync hit an edge case while moving those streams to `"version": 3` state with no previous cursor value. - Refreshing both streams moved them to correct `"version": 3` state and unblocked the connection. ### Expected behavior The new MSSQL connector should gracefully handle per-stream state migration from `"version": 2` to `"version": 3` when: - the stream had no records at migration time, - there is no previous cursor value in state, and - the stream later receives its first record. ### Actual behavior The connector appears to fail this state migration path instead of initializing the missing cursor/state for the first observed record. ### Suggested investigation - Reproduce with an MSSQL incremental stream that is empty during legacy-to-new connector migration, preserving legacy `"version": 2` stream state. - Insert the first row after migration. - Confirm the next sync migrates to `"version": 3` state without requiring a stream refresh. - Add regression coverage for the no-previous-cursor-value path. ### Workaround observed Refreshing the affected streams moved them to `"version": 3` state and unblocked syncs. --- [Devin session](https://app.devin.ai/sessions/dbc6dfdd3b5141399df1b722447c6d86) --- **Internal Tracking:** https://github.com/airbytehq/oncall/issues/12733