docs(agents): add warning for JS runtime tool registration limitation

[sasmita016]

Problem

The "Runtime tool registration" tab in the agents docs shows a JS/TS
example using wrapModelCall to add new tools at runtime. This throws:

Error: You have added a new tool in "wrapModelCall" hook of middleware "...".
This is not supported.

Reproduced in @langchain/core@1.2.26 and @langchain/langgraph@^1.0.14.
The Python version works via AgentMiddleware. The JS version does not.

Fix

Added a callout in the JS tab explaining the limitation and
pointing users to the working "Filtering pre-registered tools" approach.

References

• Unable to dynamically register tools according to the documentation. langgraphjs#1934

[github-actions]

Thanks for opening a docs PR, sasmita016! When it's ready for review, please add the relevant reviewers:

• @npentrel or @lnhsingh (LangChain)

[sasmita016]

Naomi Pentrel (@npentrel) Lauren Hirata Singh (@lnhsingh) please review and approve

[Naomi Pentrel (npentrel)]

Thanks for the report - I've tested the example in question and am not getting the issue (on "@langchain/core": "^1.1.40", "@langchain/langgraph": "^1.2.9"). I think for langchain/core 1.2.26 doesn't exist, maybe you were on 1.1.26? Can you try to update and report back?

I will also check with Christian Bromann (@christian-bromann) who might know more.

[Christian Bromann (christian-bromann)]

I will also check with Christian Bromann (Christian Bromann (@christian-bromann)) who might know more.

I can confirm that this works using the latest langchain version. sasmita016 any chance you can provide a reproduction case?