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).

---

Note

Low Risk
Documentation-only changes with no runtime, auth, or API behavior modifications.

Overview
Adds documentation for connecting Vercel Labs’ fx CLI agent to Kernel’s MCP server so it can manage cloud browser sessions and run Playwright via MCP tools.

A new integrations/vercel/fx page explains the integration, links to the fx client guide, and includes an example fx ask Hacker News scrape. The Vercel integrations overview, integrations index, and docs.json nav now point to that page.

The reference/mcp-server/clients/fx page is expanded with an OAuth issuer mismatch warning (mcp.onkernel.com vs clerk.onkernel.com), a note that interactive /mcp auth does not work for headless fx ask / fx acp / CI, and a Connect with an API key section using fx’s bearer_token_env (not static Authorization headers). reference/mcp-server/troubleshooting adds a short section on strict RFC 9207 clients and API-key fallback.

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[mintlify]

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

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[cursor]

Stale comment

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.

  

_{Sent by Cursor Automation: Assign PR reviewers}

[cursor]

Stale comment

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 HEAD (79ee9a2, +96 / -1 across 6 files) from the file diffs only. PR description and Bugbot risk claims were ignored.

Current change set (Mintlify docs site only):

• New integrations/vercel/fx.mdx integration page
• Nav entry in docs.json
• Link additions in integrations/overview.mdx and integrations/vercel/overview.mdx
• OAuth issuer-mismatch warning and API-key workaround (bearer_token_env, placeholder key) on reference/mcp-server/clients/fx.mdx
• New troubleshooting section on reference/mcp-server/troubleshooting.mdx describing the same server-side issuer mismatch and API-key workaround

Delta since last assessment (47f6190 → 79ee9a2):

• Documentation of an existing OAuth RFC 9207 issuer mismatch and the already-supported API-key path. No new pages of application logic. Still prose, callouts, and example config on the docs site.

No application code, auth/billing/permissions implementation, infrastructure, schema, or shared runtime paths changed. Documenting an existing auth bug is not an auth-model change. No CODEOWNERS file exists, so codeowner review is not required.

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

  

_{Sent by Cursor Automation: Assign PR reviewers}

[cursor]

Stale comment

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 HEAD (6ba5e36, +94 / -1 across 6 files) from the file diffs only. PR description and Bugbot risk claims were ignored.

Current change set (Mintlify docs site only):

• New integrations/vercel/fx.mdx integration page
• Nav entry in docs.json
• Link additions in integrations/overview.mdx and integrations/vercel/overview.mdx
• OAuth issuer-mismatch warning and API-key workaround (bearer_token_env, placeholder env var) on reference/mcp-server/clients/fx.mdx
• Troubleshooting section on reference/mcp-server/troubleshooting.mdx describing the same server-side issuer mismatch and API-key workaround

Delta since last assessment (79ee9a2 → 6ba5e36):

• Editorial reorder only: troubleshooting entry now leads with the workaround, then the root cause. Same content, no new files or behavior.

No application code, auth/billing/permissions implementation, infrastructure, schema, or shared runtime paths changed. Documenting an existing auth bug is not an auth-model change. No CODEOWNERS file exists, so codeowner review is not required.

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

  

_{Sent by Cursor Automation: Assign PR reviewers}

[cursor]

Stale comment

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 HEAD (4f3edd8, +92 / -1 across 6 files) from the file diffs only. PR description and Bugbot risk claims were ignored.

Current change set (Mintlify docs site only):

• New integrations/vercel/fx.mdx integration page
• Nav entry in docs.json
• Link additions in integrations/overview.mdx and integrations/vercel/overview.mdx
• OAuth failure warning and API-key workaround (bearer_token_env, placeholder env var) on reference/mcp-server/clients/fx.mdx
• Troubleshooting section on reference/mcp-server/troubleshooting.mdx pointing strict-issuer clients at the existing API-key path

Delta since last assessment (6ba5e36 → 4f3edd8):

• Editorial cut only: dropped the server-side issuer-mismatch root-cause paragraph and a cross-link sentence. Same pages, less detail, no new files or behavior.

No application code, auth/billing/permissions implementation, infrastructure, schema, or shared runtime paths changed. Documenting an existing auth workaround is not an auth-model change. No CODEOWNERS file exists, so codeowner review is not required.

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

  

_{Sent by Cursor Automation: Assign PR reviewers}

[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 HEAD (af82a39, +96 / -1 across 6 files) from the file diffs only. PR description and Bugbot risk claims were ignored.

Current change set (Mintlify docs site only):

• New integrations/vercel/fx.mdx integration page
• Nav entry in docs.json
• Link additions in integrations/overview.mdx and integrations/vercel/overview.mdx
• OAuth failure warning and API-key workaround (bearer_token_env, placeholder env var) on reference/mcp-server/clients/fx.mdx
• Troubleshooting section on reference/mcp-server/troubleshooting.mdx pointing strict-issuer clients at the existing API-key path

Delta since last assessment (4f3edd8 → af82a39):

• Editorial example swap only: fx ask prompt changed from an example.com title fetch to a Hacker News top-5 scrape, plus sample output. Same pages, no new files or behavior.

No application code, auth/billing/permissions implementation, infrastructure, schema, or shared runtime paths changed. Documenting an existing auth workaround is not an auth-model change. The fx ask string is a user-facing docs example, not a model system prompt. No CODEOWNERS file exists, so codeowner review is not required.

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

  

_{Sent by Cursor Automation: Assign PR reviewers}