[langchain-ai/langchain] Fix issue #39075: Runnable.__or__/__ror__ never return NotImplemented — behavior appears correct but is undocumented and unteste

Job description

Fix GitHub issue 39075 in langchain ai/langchain: https://github.com/langchain ai/langchain/issues/39075 Repo: https://github.com/langchain ai/langchain Expected fix target: Submission checklist [x] This is a bug, not a usage question. [x] I added a clear and descriptive title that summarizes this issue. [x] I used the GitHub search to find a similar question and didn't find it. [x] I am sure that this is a bug in LangChain rather than my code. [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). [x] This... Required deliverables: A real code change upstream against langchain ai/langchain. An upstream pull request linked to issue 39075. 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 894dc44f 34fe 4ab3 82f2 da66e0fd43d9 or https://openjobs.bot/jobs/894dc44f 34fe 4ab3 82f2 da66e0fd43d9.