docs(deepagents): add forked subagents page

[Thushanth Bengre (thushanth-bengre-langchain)]

Overview

Adds a new "Forked subagents" page documenting mode: "fork" — a declarative subagent spec (ForkedSubAgent) that inherits the parent's full conversation history and exact system prompt instead of a tool message. This feature previously had zero documentation in either language. Also adds a short teaser section to the existing subagents.mdx page linking out to the new one, and registers the page in nav for both Python and JS.

Type of change

Type: New documentation page

Related issues/PRs

• Feature PR: feat(sdk): add subagent conversation forking deepagents#5714 (Python implementation), fix(deepagents): backport Python's fork cache-parity and recursion-safety fixes deepagentsjs#800 (JS backport)

Checklist

• I have read the contributing guidelines, including the language policy
• I have tested my changes locally using docs dev
• All code examples have been tested and work correctly
• I have used root relative paths for internal links
• I have updated navigation in src/docs.json if needed

Additional notes

• No deepagents>=X.Y line yet (both source PRs still open); Will update once we release
• This PR can't pass CI (or be correct) until deepagents#5714 merges and a new PyPI release goes out.

[github-actions]

Thanks for opening a docs PR, Thushanth Bengre (@thushanth-bengre-langchain)! When it's ready for review, please add the relevant reviewers:

• @npentrel or @lnhsingh (Deep Agents)

[github-actions]

Mintlify preview branch generated: preview-bengre-1788126811-6994ab4

Site preview: https://langchain-5e9cc07a-preview-bengre-1788126811-6994ab4.mintlify.site

Important

Preview links may take a few minutes to start working while the deployment finishes.

Changed documentation pages (preview deep links):

• src/oss/deepagents/forked-subagents.mdx
• src/oss/deepagents/subagents.mdx