ECO-639: Document the X-Agent-Info attribution header

[wkoutre]

Linear

https://linear.app/uniswap/issue/ECO-639

Summary

Adds developer docs for the optional X-Agent-Info request header (AI-agent traffic attribution on the Trading API):

• New page content/trading/swapping-api/agent-attribution.mdx: the three-field request schema (decision_origin, integration_name, version), every rule that marks the header malformed, and the x-agent-info-status response contract used to confirm it parsed — with a worked cURL + TypeScript example.
• meta.json: adds the new page to the Swapping API nav, after Integration Guide.
• Cross-links from integration-guide.mdx (Authentication section), common-errors.mdx (Headers troubleshooting), and uniswap-ai/overview.mdx (AI-agent audience).

Schema and malformed-detection rules were verified directly against Linear ECO-634 and the backend implementation PR body (Uniswap/backend#11003), not just the docs ticket's own description — two real gaps (the "successful responses only" gating on the diagnostic response header, and the empty-string-is-absent-not-malformed case) were caught by an independent review pass and fixed before this PR was opened.

⚠️ Timing — please read before merging

1. The backend feature this documents is not yet deployed. Uniswap/backend#11003 (parsing + the x-agent-info-status response header) and its base stack (#11002 → substreams#670) are all still open, unmerged as of 2026-08-02. The automated security gate passed, but the PR carries an explicit "do not merge before SECURE-274 appsec review closes" note. ECO-634 (the gateway ticket) is in "In Review", not Done. Recommend holding this docs PR until the backend stack merges and the entry-gateway CORS/Pulumi change actually deploys — otherwise these docs describe a header that silently does nothing in production yet.
2. This repo doesn't build developers.uniswap.org directly. Per this repo's own README.md/CONTRIBUTING.md (added in the recent content/-restructure), Uniswap/docs is a downstream mirror: accepted changes are ported into a separate, private publishing pipeline in batches, and may go live before or after they land here. So there's already a natural delay before this PR (once merged) reaches the live site — worth knowing when coordinating with navbar links fallback to most recent version instead of current version #1 above.
3. llms.txt / llms-full.txt are not files in this repo. No static llms.txt exists under content/; the previous (now-archived) Docusaurus site generated it from doc content at build time via docusaurus-plugin-llms, and content/uniswap-ai/overview.mdx describes the same live behavior today at developers.uniswap.org/llms.txt. This strongly suggests the new pipeline auto-generates it from content/ the same way — meaning this page should flow into llms.txt/llms-full.txt automatically once ported — but I don't have visibility into that separate pipeline's repo to confirm directly.

Test plan

• Validated meta.json is well-formed JSON and the new page's nav entry matches its filename.
• Verified every internal link/anchor added resolves to a real heading in the target page.
• Independent review pass (fresh-context reviewer) checked the schema, malformed rules, and response contract word-for-word against ECO-634 and backend PR #11003; two gaps found and fixed (see Summary).
• No local build/lint tooling exists in this repo for content/ (no root package.json) — nothing further to run.

🤖 Autonomously generated by the Linear Task Worker.

[github-actions]

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