[BUG] Incorrect URL format in citation reference

[YujingYang666777]

Describe the bug
After asking the question, sherpa provides a solution with a reference. However, the reference does not follow the desired format.

To Reproduce
This bug randomly appears. Asking the same question may not get the same result.

Expected behavior
We expect a number and URL in the reference.

Screenshots
here is the returned result:
Please refer to the Langchain documentation for more detailed information and examples on using Langchain with SQL databases. [1]
[1] SQL Chain example [DocID:1]

Note: it should not have " [DocID:1]" within the reference

Environment
development environment in the main branch

Additional context

[20001LastOrder]

Closed by #241