Add fx integration guide, document headless MCP auth

[dprevoznik]

Summary

• Adds integrations/vercel/fx.mdx, an integration guide for connecting fx (Vercel Labs' native CLI coding agent) to Kernel's MCP server, and links it from integrations/overview.mdx, integrations/vercel/overview.mdx, and the nav.
• Documents a gap in the existing reference/mcp-server/clients/fx.mdx page: the OAuth flow kernel mcp install --target fx sets up only works in an interactive fx session. Non-interactive runs (fx ask, fx acp, CI) need a Kernel API key via fx's bearer_token_env field instead — fx rejects a literal Authorization header, so the generic API-key pattern used on other client pages doesn't apply here.

Test plan

Verified end-to-end in a scratch environment before writing anything down:

• Installed fx 0.0.7, confirmed it authenticates against the model provider with no extra setup
• Configured ~/.fx/mcp.json with bearer_token_env pointing at a Kernel API key
• Ran fx ask with a prompt to create a browser session, run execute_playwright_code against https://example.com, and delete the session — got back the correct page title and confirmed via kernel browser list that the session was cleaned up
• Confirmed the OAuth config written by kernel mcp install --target fx fails in non-interactive fx ask with the exact error now documented on the client page
• docs.json validated as JSON

Not run: mintlify broken-links (exits non-zero in this sandbox with no other output, likely a network/environment issue unrelated to this change).

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Note

Low Risk
Documentation-only changes with no runtime or security logic modifications.

Overview
Adds documentation for connecting Vercel Labs' fx CLI agent to Kernel's MCP server so users can spin up cloud browsers from fx prompts.

A new integrations/vercel/fx.mdx page explains the integration (on-demand MCP tool discovery, Playwright via execute_playwright_code) and includes an fx ask example. It's wired into docs.json, integrations/overview.mdx, and integrations/vercel/overview.mdx.

reference/mcp-server/clients/fx.mdx gains a Headless and scripted use section: OAuth from kernel mcp install --target fx only works interactively; fx ask, fx acp, and CI need a Kernel API key via fx's bearer_token_env (not a static Authorization header).

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Project	Status	Preview	Updated (UTC)
Kernel	🟢 Ready	View Preview	Aug 29, 2026, 9:53 PM

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[cursor]

Risk assessment: Very Low

Decision: Approval stands. Risk did not increase after the latest push. Not re-approving (already approved on 46e4c55).

Re-evaluated the current diff (+75 / -1 across 5 files) independently of the PR description.

Current change set (docs site only):

• New integrations/vercel/fx.mdx integration page
• One nav entry in docs.json
• Link additions in integrations/overview.mdx and integrations/vercel/overview.mdx
• New “Headless and scripted use” section on reference/mcp-server/clients/fx.mdx (placeholder sk_..., env-var auth via bearer_token_env)

Delta since prior approval (46e4c55 → 47f6190):

• Editorial trim only: removed a duplicated Setup section from integrations/vercel/fx.mdx and replaced it with a pointer to the existing MCP client guide. Smaller surface than the previously approved revision.

No application code, auth/billing/permissions logic, infrastructure, schema, or shared runtime paths changed. No CODEOWNERS file exists, so codeowner review is not required.

Fits the Very Low criteria: documentation-only, small scoped diff, no production logic or infra impact.

  

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