Plumbing.

The thesis.

Plumbing is the catalogue’s piece of infrastructure. It is not an orchestration language in the sense Boruna, Pel, or Marsha are — it is the typed substrate that orchestration languages can be expressed on top of. Where existing agent frameworks (n8n, LangGraph, CrewAI) coordinate agents with ad hoc engineering, Plumbing coordinates them with morphisms in a copy-discard symmetric monoidal category. Objects are typed channels: !A is a stream of As, !string a stream of strings. Morphisms are processes with typed inputs and outputs. Four structural morphisms (copy, discard, merge, barrier) plus two utilities (map, filter) compose sequentially and via the tensor product. The compiler statically checks that every wiring is well-formed before any agent runs.

Static typing prevents the waste.

The distinctive move is to refuse the orchestration camp’s normal framing. Where Boruna treats the unit of computation as an .ax workflow with declared effects, and Pel treats it as a grammar-level capability, Plumbing treats the unit as a channel between two processes, with the agent itself reduced to a stateful morphism with a typed protocol — main input, main output, plus control ports for runtime parameter modulation (e.g. temperature), tool-call ports, operator-in-the-loop ports, and telemetry. A judge agent that wants to cool down a debate sends a set_temp message on the debaters’ control ports; the wiring is type-checked the same as the data path.

What it looks like.

type Verdict = { verdict: bool, commentary: string, draft: string }
type Review  = { score: int, review: string, draft: string }
let composer : !string  -> !string  = agent { … }
let checker  : !string  -> !Verdict = agent { … }
let critic   : !Verdict -> !Review  = agent { … }
let main : !string -> !string = plumb(input, output) {
input   ; composer ; checker
checker ; filter(verdict = false)
; map({verdict, commentary}) ; composer
checker ; filter(verdict = true) ; critic
critic  ; filter(score < 85)
; map({score, review}) ; composer
critic  ; filter(score >= 85).draft ; output
}

Distinctive moves.

• Typed channels, not typed messages. Objects in the category are streams. !A is a stream of As; sequential composition glues stream-producing morphisms; the tensor product runs them in parallel. Well-formedness is a category-theoretic property, checked at compile time.
• Four structural morphisms. Copy duplicates a stream, discard throws it away, merge interleaves two streams of the same type (after coproduct injection), barrier synchronises two streams into a pair. Barrier is the synchronisation primitive that unlocks session types.
• Agents as stateful morphisms with control ports. An agent has main input/output plus typed control, tool, operator-in-the-loop, and telemetry ports. Runtime parameter changes (e.g. temperature) flow through the same typed pipework as data.
• The κ-calculus “don’t care, don’t write” convention. Any output port not mentioned in the program is implicitly connected to discard. The textual surface stays small while the type system still tracks every port.
• MCP server in the release. The first public drop ships a compiler, an interpreter, and an MCP server — agent harnesses are first-class consumers of the language, not an afterthought.

Maturity.

Version 0p1, first public release March 2026, binary downloads for Linux x86_64 and macOS Apple Silicon. The release ships a compiler, interpreter, and MCP server. There is no public Git repository; the licence is free for educational and personal use, with a separate commercial licence available from Leith Document Company. The author is William Waites, a Chancellor’s Fellow at the University of Strathclyde; the broader programme of work is described in his arXiv paper Artificial organisations (arXiv:2602.13275). A second blog post, “The agent that doesn’t know itself,” extends the calculus with session types and context compaction.

The bet is that orchestration languages eventually need a category-theoretic substrate underneath them, and that the substrate is more valuable as a typed coordination layer than as another orchestration framework competing for workflow attention.

Agent tooling.

The release includes an MCP server alongside the compiler and interpreter, which is the entire agent-facing surface — there is no SKILL.md, AGENTS.md, or CLAUDE.md in this drop, because Plumbing’s framing is that the language is the agent tooling for everything above it. Agent harnesses consume Plumbing through MCP; what agents author in Plumbing is the wiring diagram for other agents.