Prototype

prototype

The prototype-first path to a feature (see ${CLAUDE_PLUGIN_ROOT}/references/two-paths.md). Build a rough working thing fast and iterate it — no feature list, no stories, just the concept and rounds — until it converges. No ACs, no plan, no tests, no gates, no gauntlet: there is nothing to grade against yet, because the prototype is what everything else will be graded against. Most prototypes are learning; the ones worth keeping convert to spec — reaching the same fully-specced, hardened feature as spec-first, by build-then-spec instead of spec-then-build.

The iteration loop is the point — it is where the speed comes from. Expect several rounds; the "one thing it must demonstrate" sharpens as you go.

Sits before discuss/feature-init in ceremony: discuss talks an idea through; prototype builds it to find out. discuss and feature-init offer this path as a first-class entry.

When to use

• /engineer.prototype "<idea>" — spike an idea into a runnable rough cut.
• The core question is "what would this even look like / feel like / do?" and a paragraph of spec won't answer it but ten minutes of code will.

Not for: the real build (that's the pipeline, post-promote); anything that must be correct, tested, or hardened; grading a prototype with the gauntlet (there is no bar yet — this is the bar).

Workflow

1. Resolve + load — methodology root + manifest via ${CLAUDE_PLUGIN_ROOT}/scripts/dae_resolve.py (see references/resolving.md). Load CHARTER.md for the stack/conventions to build in, and the last ~15 lines of .engineer/prototypes.log to soft-match against existing prototypes and Ready features (don't re-spike something that already exists).
2. Frame in two lines — the rough idea, and the one thing it must demonstrate (the question the prototype answers). Not a spec. Derive a kebab slug from the idea. If an idea arg was given, use it; otherwise ask once.
3. Build rough — construct the minimum runnable thing that answers the question. Speed over quality: hardcode, stub, fake data, skip error paths, no abstractions, no tests. Match the charter's stack so it's recognizable, but nothing here is load-bearing. Keep it runnable — a prototype that can't be opened/run is worthless as a bar. Build directly (or one born-die builder for a big one); no multi-agent gauntlet, no CP gates. Land it in prototypes/<slug>/; ensure prototypes/ is in .gitignore (throwaway by default).
4. Capture — write prototypes/<slug>/PROTOTYPE.md: the idea, the one thing it demonstrates, how to run it, what's faked/stubbed/hardcoded, and the open questions it surfaced. This is the "prototype is the spec" record — the human-readable intent + result. Show the user how to see it (run command, or SendUserFile for a visual artifact). Append one line to .engineer/prototypes.log: <ISO-timestamp> | <slug> | built | <one-line what>.
5. Decide (human) — recommend an outcome; the user confirms. Never auto-execute.
   • Iterate (the default while learning) — rebuild with feedback, same dir, still zero ceremony (iteration 0.x). Update PROTOTYPE.md. Stay here for as many rounds as it takes — convergence, not round count, is the exit. This loop is where the speed lives; don't rush out of it.
   • Discard — rm -rf prototypes/<slug>/; log line ... | discarded | <why>. The learning stays in the log.
   • Convert to spec (promote) — the concept has converged and earned a real build. This is the pivot from prototype-first into the pipeline (see ${CLAUDE_PLUGIN_ROOT}/references/two-paths.md): a. Invoke feature-init with feature_intake { status: ready, ... } — seed outcome/title from PROTOTYPE.md, carry size if obvious. b. Copy prototypes/<slug>/ → features/NNN-<slug>/prototype/ (tracked, so the bar travels with the feature to any agent/host), and record prototype: prototype/ in feature.md frontmatter. Discard the gitignored original. c. Set the disposition (size-dialed) — record prototype_disposition: in-place | rebuild in feature.md (defaulted from size, overridable): S/M → in-place (the prototype code is CP5's starting implementation; refine + verify + harden clean it); L/XL or risky → rebuild (CP5 implements fresh against the derived spec, with the prototype as the gauntlet: bar; its code is discarded). d. Hand off to discover-acs in reverse-engineer mode with the prototype + PROTOTYPE.md as the seed — this is "convert the artifact to ACs," the same RE mode onboarding uses. The prototype is iteration 0; plan (CP4) reads prototype: and declares it as the gauntlet: bar (see references/gauntlet.md). e. Log ... | promoted | features/NNN-<slug>/.