DESIGN.md@tests/tla/mcp_call/designA
DESIGN.md@tests/tla/mcp_call/design from vercel-labs/fx is a DESIGN.md file: the design rules coding agents follow in that repo.
mdr add vercel-labs/fx/tests/tla/mcp_call/design/DESIGN.md@git:20261030.965ced5Pins git:20261030.965ced5 in mdr.lock. Pin the fingerprint instead.
- Audit grade
- A, 14 of 14 checks passed
- Kind
- DESIGN.md file
- Repository
- vercel-labs/fx
- Path
tests/tla/mcp_call/design/DESIGN.md- Versions recorded
- 5
- Latest version
- git:20261030.965ced5, committed Oct 30, 2026
- First version recorded
- Oct 29, 2026
- Size
- 30,781 bytes
- Repository stars
- 3,794
- License
- Apache-2.0
Collected from public GitHub. Every version is saved exactly as it was and never changes. Install it at an exact version with the mdr tool, and every file is checked before it reaches your agent. The main file is checked against the SHA-256 fingerprint recorded here, and the others against the fingerprints GitHub keeps for its source commit. The automatic checks below grade the latest version, and the same checks always give the same file the same grade.
What the file says
# Design: `fx mcp call` bridge How a running fx session takes MCP tool calls from the commands its shell runs, so the agent can send a large result to a file or a pipe instead of into its context. `CONTEXT.md` describes the code on `6bb36a928`. Line numbers here refer to that commit, except those marked "this change", which refer to this worktree. `tests/tla/drivers/mcp_call/traceability.ts` reads this file. It requires: - every question below to be answered or listed as not applicable; - every rule and law to have a row under Enforcement; - every law to name a planted bug; - every entry there to name a check that exists. ## Questions - Q1: Values cross only as references or small typed fields. The client sends one JSON line (token, version, and an operation: a call's tool and arguments, or a lookup's server, query, or tool) over the session's socket. The core gets a 32-byte token, a version, request ids, and enums (`mcp_call.zig:115-132`, this change). Arguments and results stay in the shell by request id. The result crosses once, from the session to the client's standard output, and the model sees only what the agent prints. Logs get request ids and drop kinds, never tokens… …
Read the whole file at its exact version.
How to install
mdr add vercel-labs/fx/tests/tla/mcp_call/design/DESIGN.md@sha256:bb8a9261c689aa23The line at the top of this page pins the label git:20261030.965ced5, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
[](https://markdownregistry.com/a/art_3j3vq5cmzhpvltgy)
2 badge image fetches in 30 days. What the badge shows.
Versions
The registry has recorded 5 versions of this file, between Oct 29, 2026 and Oct 30, 2026, more than one a day.
| version | committed | commit | size | audit | |
|---|---|---|---|---|---|
| git:20261030.965ced5 latest | 2026-10-30 | 965ced5 | 30,781 B | A | view · diff |
| git:20261030.4f26d9f | 2026-10-30 | 4f26d9f | 30,541 B | A | view · diff |
| git:20261030.138d5de | 2026-10-30 | 138d5de | 27,960 B | A | view · diff |
| git:20261029.b8b5056 | 2026-10-29 | b8b5056 | 27,875 B | A | view · diff |
| git:20261029.6579f9c | 2026-10-29 | 6579f9c | 27,435 B | A | view |
Audit of the latest version
- pass: Size between 200 bytes and 200 KB (30781 bytes)
- pass: No zero-width or bidi control characters
- pass: No instruction hidden inside an HTML comment
- pass: No link to an exfiltration or paste host
- pass: No credential-shaped string
- pass: No instruction to send local credentials anywhere
- pass: No text hidden with inline styles
- pass: No prompt-injection phrasing
- pass: No curl or wget piped into a shell
- pass: No recursive delete of root, home or parent
- pass: No instruction to read or print local credentials
- pass: No base64 blob over 200 characters
- pass: No link to a raw IP address
- pass: No script tag
Source
vercel-labs/fx · 3,794 stars · license Apache-2.0 · pushed 2026-11-08 · branch main
API
GET https://markdownregistry.com/api/v1/artifacts/art_3j3vq5cmzhpvltgy GET https://markdownregistry.com/api/v1/resolve?ref=vercel-labs/fx/tests/tla/mcp_call/design/DESIGN.md GET https://markdownregistry.com/api/v1/blob/bb8a9261c689aa231620e662b1bd3adee38fb569ce171e6947d25300446d9815
Your AI assistant does the legwork. You hear about the deals worth your word. Hand yours the standing instructions at modelranch.com and it joins the network that reads files like this one.
Guides: what DESIGN.md is and how agents use it · which agent file does what.