# Fable Engine

> Turn a plain-English vision or task into a verified, build-ready spec before any code. Locks the finish line, researches across channels, enforces the Evidence Standard, stops at the human gate. Adopted from CleanExpo/Fabel-Prompt-Engineer for the Synthex build process.

- Skill: `cleanexpo/fable-engine` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cleanexpo/fable-engine`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cleanexpo/fable-engine/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: cleanexpo (https://skillmd.com/u/cleanexpo)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cleanexpo/fable-engine

---


# Fable Engine (Synthex build process)

Input: a vague idea or a non-trivial change in plain English. Output: a precise,
sourced, build-ready spec. You propose; the human decides. Pairs with
`.claude/rules/fabel-evidence-standard.md` and `.claude/FABEL_PLAYBOOK.md`.

Use it for: a new feature, a workstream/elevation wave, a risky refactor, or any
multi-agent fan-out. Skip it for: a one-line fix or a conversational answer
(Fabel directive 1 — act when you have enough info).

## Operating loop

### 1. Lock the finish line

Restate the task as one testable sentence: _"Done when \_\_\_."_ If several finish
lines are plausible, pick the most likely, state it, list the rejected ones.
Emit: `[STATUS] finish-line: locked — <one sentence>`

### 2. Research channels (emit started/done per channel)

- **Source channel** — read the actual Synthex code + `.claude/` rules that
  constrain or accelerate the change. Docs are stale; the source is truth.
- **Prior-work channel** — search merged PRs, `.claude/scratchpad`, memories,
  and open PRs for decisions and existing patterns (e.g. `defineRoute`,
  `getEffectiveOrganizationId`, the deploy-pipeline gotchas).
- **Web channel** — for external facts (API shapes, prices, library versions)
  use Context7 / web; every web finding carries its source URL. No web access →
  mark skipped, downgrade affected claims to `[UNCONFIRMED]`.

### 3. Filter through the Evidence Standard

Every finding and spec claim is tagged `[VERIFIED]` / `[INFERENCE]` /
`[UNCONFIRMED]` per `fabel-evidence-standard.md`. An untagged claim is a defect.

### 4. Synthesize, ask only what you can't infer

Draft the spec. Infer-and-tag rather than ask. Where info is genuinely missing,
list ≤5 concrete, answerable questions.

### 5. Board critique (high-stakes or on request)

Run `boardroom` / `ask-the-board` on the draft; append the combined critique as
a lens. Label it `[INFERENCE] — persona synthesis, not fact`. It feeds the gate,
never bypasses it.

### 6. Approval gate

Present the spec and stop. Nothing builds until the human approves. For the
agent fleet: the spec is the contract each subagent is dispatched against, and
the prod-deploy gate remains the founder's call.
Emit: `[STATUS] gate: awaiting approval`

## Spec output format

1. **Finish line** — the locked "done when" sentence.
2. **Decision up front** — recommended path in one paragraph.
3. **Goals & non-goals** — non-goals required.
4. **Approach** — plain language first.
5. **Phased plan** — smallest phase first; each phase has a definition of done;
   no later phase before the earlier DoD is met. For a fleet wave: the disjoint
   agent lanes + their file boundaries.
6. **Data model** — if it stores anything (respect the Synthex migration rules:
   `apply_migration` only, never `prisma db push`).
7. **Security & cost guardrails** — secrets, org-scoping, spend; structural not
   advisory.
8. **Risk & assumption register** — every `[UNCONFIRMED]` lands here.
9. **Open questions** — the ≤5 from step 4, if any.
10. **Verification plan** — the exact commands that will prove "done"
    (`build:vercel`, `npm test -- --coverage`, the integration gauntlet). Per
    Fabel directive 5, a claim isn't done until its tool result says so.

## Status grammar

`[STATUS] <subject>: <state>[ — detail]` — subjects: `finish-line`,
`channel:source`, `channel:prior-work`, `channel:web`, `synthesis`, `board`,
`gate`.