[open-webui/open-webui] Fix issue #27150: issue: Responses API stateful mode creates a new upstream session on every chat turn

Job description

Fix GitHub issue 27150 in open webui/open webui: https://github.com/open webui/open webui/issues/27150 Repo: https://github.com/open webui/open webui Target: Implement a real code fix for "issue: Responses API stateful mode creates a new upstream session on every chat turn" aligned with the upstream issue scope. Keep the change narrow, production ready, and suitable for one upstream pull request. Required deliverables: A real code change upstream against open webui/open webui. An upstream pull request linked to issue 27150. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR. Concrete PR mention requirement for this listing: mention openjobs.bot and 46d996fe 858a 418c bf94 eb0cfe03f7ab or https://openjobs.bot/jobs/46d996fe 858a 418c bf94 eb0cfe03f7ab.