elcoosp

Louis Cospain

Rust engineer with a product-builder's track record. Eight years shipping TypeScript to production — six of them at Weenat (agri-tech, 10k+ IoT sensors, live on the App Store & Google Play). Since 2024 I have bet on Rust full-time and built everything in public: complete systems with specs, ADRs, test suites and CI — not tutorials.

Recent output: a framework-agnostic full-stack meta-framework (oxide), a reactive abstraction layer (quoin), an end-to-end HUNL poker AI (pkr-sota), and massive ongoing work on kod, glyim, and flux.

// this profile, as code
let shipped = vec!["flux", "kod", "vautr", "glyim", "stackbluff", "oxide", "quoin", "pkr-sota"];
debug_assert!(shipped.iter().all(|p| is_public(p) && is_spec_driven(p) && is_tested(p)));

let next = Role::rust().in_france(&["Nantes", "Paris", "remote"]);
// interested? -> elcoosp@gmail.com

Flagship Rust Work

Repository	What it is	Receipts
oxide	Framework-agnostic full-stack meta-framework with a Rust core. React, Vue, Svelte, and Solid over one shared engine. Compiles to a single static binary, ships to 12 deploy targets.	18 crates · ODF binary wire format · 3-tier cache · 2,300+ commits in Oct 2026
quoin	Framework-agnostic reactive abstraction layer for Rust. Write reactive business logic once using signals and effects, run across GPUI, Leptos, Dioxus, Xilem, or Floem.	Unified Reactive API · Declarative macros · Tailwind class transpilation
kod	Local-first AI coding-agent harness (TUI + CLI). Streaming agentic loop, multi-agent swarm, MCP & LSP clients, sandboxed shell, JSONL session audit. Your code never leaves your machine.	20 crates · ~4000 tests · Landlock / bwrap / sandbox-exec · 1,300+ commits in Oct 2026
glyim	From-scratch compiler for a Rust-like systems language, written in Rust: lexing -> HIR/MIR -> type inference & trait solving -> NLL borrow checking.	Full pipeline, no rustc internals · 580+ commits in Oct 2026
pkr-sota	End-to-end heads-up No-Limit Hold'em poker AI in Rust. Precompute, train, export, and query a CFR blueprint on a single machine with nanosecond lookup times.	Deterministic training · mmap blueprint loading · p50 ≈ 42ns queries · 460+ tests
vautr	Zero-knowledge password manager: OPAQUE authentication + Argon2id, offline-first sync. The server never sees your secrets.	Rust core · React / Expo / GPUI clients · AGPL, self-hostable forever
flux	Write-once UI language for native iOS & Android. Hot-reload on-device as binary IR patches over WebSocket — release builds compile to real SwiftUI & Jetpack Compose.	16 crates · ~63k LOC of Rust · 92 golden ISA vectors · 39 ADRs
stackbluff	Multiplayer poker platform: sub-10ms Rust engine, AI coach, bots, anti-cheat, clubs & tournaments, Stripe billing.	Built end-to-end by 5 parallel AI agents

TypeScript & Full-Stack Work

Repository	What it is	Receipts
takumi-motion	Deterministic server-side animation engine that renders React components or HTML to GIF, WebP, or APNG.	TypeScript/React integration · Server-side rendering pipeline · Created Oct 2026

Production Track Record (Pre-Rust)

Weenat — agri-tech, 6 years full-stack TypeScript
- 10k+ IoT weather sensors in production; mobile app live on App Store & Google Play
- Led the React Native/JS -> Expo/TypeScript migration across mobile & web
- Built the IoT alert microservice (Node.js, AWS SQS)
- Shipped a back-office letting marketing manage 5 languages with zero dev tickets

How I Work

Spec before code — flux carries 39 MADR ADRs plus a full wire-protocol & VM-ISA spec; kod ships SPEC, ARCHITECTURE and TESTING documents; oxide maintains strict spec-vs-code deviation docs.
Tests are the design review — cargo-nextest, proptest, insta snapshots, criterion performance budgets (parse < 5 ms, diff < 1 ms, VM eval < 2 ms); ~4000 tests across kod's crates; Miri-clean core crates in pkr-sota.
CI like it's production — clippy -D warnings, #![forbid(unsafe_code)] in every library crate, fuzzed wire protocol, mutation testing, parity harnesses, golden-hash CI gates.
AI-augmented, engineer-owned — I ship daily with AI & MCP, and I built my own harness (kod) to keep the loop local, sandboxed and auditable.

Currently (October 2026)

oxide: Fixing website routing/CSS injection across render paths, refining the CLI/router scanner, and expanding documentation (local dev, CI, release, security) while enforcing workspace-wide build checks.
quoin: Implementing proper JoinHandle abort/detach semantics and fixing request_update recursion across all framework adapters (GPUI, Leptos, Dioxus, Xilem, Floem). Bounding cancellation waker registries to prevent memory leaks.
kod: Refactoring tools.rs by extracting shared helpers (atomic_write, kill_child_tree) to enable parallel tool splits. Closed v0.1.27 audit sweep with memory obfuscation fixes and documented the main-loop split proposal.
glyim: Fixing signed wrapping arithmetic and literal receiver method resolution. Investigating a critical LLVM backend miscompile where checked_* operations on signed integers incorrectly used unsigned intrinsics, requiring a coordinated fix across typeck, interp, and LLVM backends.
pkr-sota: Shipped K=7 action abstraction, but documented a +261 mbb regression in run 1 ("DO NOT SHIP"). Measured Phase 5 infeasibility at current resolution (time bottleneck) and corrected audit claims about memory size (UndoRecord is the dominant cost). Fixed parallel test temp-file races.
flux: Expanding ISA vector coverage for uncovered opcodes (remove_item_basic, clear_basic), fixing BOOL_EQ operand lengths, and ensuring content_address gracefully handles dangling child references without panicking.

Open To

Rust engineer roles — backend, systems, product or security-adjacent. France (Nantes / Paris) or remote. I want a long-term product team where I own features end-to-end and keep shipping. Bonus points if the roadmap touches compilers, real-time, developer tooling, reactive systems, or applied crypto — that is where my public work lives.

Stack

Rust ecosystem, in anger: tokio · axum · clap · ratatui · redb · blake3 · MessagePack · proptest · insta · criterion · cargo-nextest · OpenTelemetry · hyper · rustls · Oxc · Rolldown

Stats

Everything I build is public. If any of it is interesting to you — let's talk.

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