effect-at-opencode

A Slidev deck — spliced over the speaker video — that showcases how opencode uses Effect (v4 / effect-smol), built directly from the real opencode codebase and from Dax Raad's talk "Effect at OpenCode" (Effect Miami 2026).

The idea (per the original tweet):

opencode run "take the transcript and make a slidev based on the opencode repo to showcase the usage of effect then splice that slideshow over the speaker video"

What's here

Path	What it is
slides/	The Slidev deck (slides.md, 17 slides) + timings.json sync map
scripts/	Render + splice pipeline (PNG export → slide track → composite)
PLAN.md	The build plan — phases, deliverables, slide-to-code mapping
overview.md	Distilled technical summary of the talk (the five Effect patterns)
transcript.md	Full timestamped transcript of the talk
.context/opencode	Git submodule — opencode source, the ground truth for every code slide
.context/effect-v4	Git submodule — effect-smol (Effect v4), the library opencode targets

Building the deck

cd slides && npm install        # one-time (also pulls playwright-chromium)
npm run dev                      # live-preview the deck at localhost:3030
npm run build                    # static site → slides/dist/

Rendering the video

The deck is spliced over the speaker video in two steps (both need ffmpeg on PATH):

# Phase 3 — export slides to PNG and build a timed, silent slide track.
node scripts/render-slide-track.mjs        # → build/slide-track.mp4

# Phase 4 — composite the speaker video as picture-in-picture over the slides.
node scripts/splice.mjs <speaker-video.mp4>   # → build/final.mp4

scripts/render-slide-track.mjs reads slides/timings.json (slide index → talk timestamp) to hold each slide for the right interval, so the two tracks line up when both start at 00:00. The PNG export and concat-file generation run without ffmpeg; only the final mux/splice require it.

Getting started

This repo uses git submodules for the reference code. Clone with:

git clone --recurse-submodules https://github.com/bjacobso/effect-at-opencode.git

Or, if you already cloned it:

git submodule update --init --recursive

The submodules are pinned to specific commits so the slide line-references stay stable:

• opencode → sst/opencode
• effect-v4 → Effect-TS/effect-smol

The five patterns

The talk walks through five concrete places opencode leans on Effect. Each maps to real files in the submodule (see overview.md and PLAN.md for the full mapping):

1. Schema & branded types — provider/schema.ts (ProviderID, ModelID)
2. Services & layers (DDD) — git/index.ts (GitService, swappable impls)
3. PubSub & Streams — bus/index.ts (event bus over Effect PubSub → Stream)
4. OpenTelemetry tracing — auto-instrumented spans, fed back into the agent loop
5. Strictly-typed HTTP server — server/routes/.../httpapi/ (HttpApi, additive OpenAPI)

Why

opencode hit ~8M monthly active users; at that scale the edge cases everyone skips (cancellation, interrupts, clean shutdown, abort signals) became thousands of daily bugs. Effect's explicit, codified patterns both enforce correctness and give LLMs strong guardrails — verbose code is fine when the AI is the one typing it.