docs: add Deep Agents integration page

[r-marques]

What

Adds integrate/add-to-your-agent/deep-agents.mdx — a guide for charging for a capability that lives inside a Deep Agents subagent.

@requires_payment works on the Deep Agents harness unchanged, including on a tool one task() delegation hop away from where the buyer supplied the token. LangGraph copies configurable into subagent tool calls, so the decorator still finds config.configurable.payment_token. That property is what makes the harness usable for monetized capabilities at all — a deep agent's premise is that the supervisor hands work to subagents — and nothing documented it.

Contents

• The delegation hop, with a diagram of where the token enters and where it is read.
• A quick start that puts the paid tool only on the subagent, so every paid call crosses the boundary.
• Deployment (unchanged — create_deep_agent() returns a compiled graph, so langgraph.json works as-is).
• The LangChain v1 version floor (langchain-core>=1.6.1) and why the agent usually wants its own virtualenv.
• Two harness behaviours that are easy to miss:
  • a deep agent decides for itself how many subagent calls a request warrants, so one user turn can settle credits several times — cap it per run;
  • two LLM layers can paraphrase the paid tool's output, or worse, answer from their own knowledge and give the capability away free.
• A harness comparison table against plain create_react_agent.

Also adds the nav entry in docs.json (edited as text) and a cross-link <Note> from the LangChain page.

Verification

mintlify broken-links → no broken links. Because that check can go green having scanned nothing when MDX fails to parse, I also ran a canary: a deliberately broken link in the new page was caught (found 1 broken links in 1 files), then reverted — so the green is real.

Related

• SDK: test(x402): pin Deep Agents compatibility for @requires_payment payments-py#267 (compat tests + API-reference section)
• Tutorial: langchain-deep-agent-py

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[aaitor]

🤖 Fallback review bot picking this up.

[aaitor]

Fallback docs review (docs#336) — new Deep Agents integration page + nav entry + a langchain.mdx cross-link.

Checked the code samples against the actual SDK rather than eyeballing them: payments_py.x402.langchain exports requires_payment / PaymentRequiredError / last_settlement at the #267 head, and the decorator signature matches its docstring — so the imports and usage are real. The delegation-hop explanation and the two harness caveats (multi-billing per turn, supervisor answering from its own knowledge) match the behaviour the PR describes. Nav (docs.json) and the reciprocal langchain.mdx note are both in place.

No blockers, no should-fix. Nice page.

[aaitor]

✅ Approved — no blockers, nothing to address.

Inline review: #336 (review)