[Bug] [core/indexer] PR #25754 seems like introducing bugs

[KeiichiHirobe]

Checked other resources

• [X] I added a very descriptive title to this issue.
• [X] I searched the LangChain documentation with the integrated search.
• [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).

Example Code

None

Error Message and Stack Trace (if applicable)

None

Description

https://github.com/langchain-ai/langchain/pull/25754 seems like introducing bugs.

Let's say we have 3 records a, b, c with the same source_id, and someone will delete the record c. The indexer should delete a record for c from vector database and record manager, but it won't after the PR was merged because docs_to_index doesn't include the source_id.

System Info

None