# Spec Structure Governance

> Partial Skill: invoke by name only — the SDD project-spec organization contract: what kind of node a spec is and where that kind lives. Loaded by scaffold-project-spec, place-node, the formation Warden, and the architect bars, not user-triggered.

- Skill: `cyberuni/spec-structure-governance` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add cyberuni/spec-structure-governance`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberuni/spec-structure-governance/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: cyberuni (https://skillmd.com/u/cyberuni)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberuni/spec-structure-governance

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# SDD Spec-Structure Governance

What kind of node a spec is, and **where that kind lives** in the project spec. This skill is the
canonical home consumers load instead of restating it — `scaffold-project-spec` when it lays a tree
out, `place-node` when it suggests a home, the formation **Warden** when it audits structure, and the
**architect** bars when they judge placement.

Taxonomy and placement are **one rule, not two**: the placement law is the taxonomy applied to
folders, and cannot be stated without it. A descriptive doc in `design/` is correct where a
behavioral node in the same folder is a defect — the folder alone does not say which.

The lifecycle a spec moves through is `sdd:lifecycle-governance`; a node's internal section shape is
`sdd:spec-format-governance`; how the suite is written is `sdd:suite-format-governance`.

## The node taxonomy — three kinds, declared

| Kind | Subject | Owns a suite | Carries | Marker |
|---|---|---|---|---|
| **descriptive** | none | no | ordinary prose | *(none — the default)* |
| **reference artifact** | a real thing with no testable surface of its own | no, by design | `## Subject` in place of `## Use Cases` | `spec-type: reference` |
| **behavioral artifact** | a testable subject | **yes** | the node sections | `spec-type: behavioral` |

**Declared, never inferred.** The kind lives in frontmatter. Inference breaks both ways: a behavioral
node has no suite *yet* while it is being authored, and descriptive indexes live outside the rules
folder — so neither file-presence nor location classifies reliably. Declaring it up front makes an
unfinished behavioral node read as **incomplete** rather than as an index.

A **capability** is what the project *does*. The everyday word for one behavioral node is a **unit
spec**.

## Placement — the taxonomy applied to folders

**Screaming architecture** is the default: top-level folders are named for **capabilities**, so the
folder names say what the project does. Three folders are deliberately *not* capabilities:

| Folder | Holds |
|---|---|
| `design/` | the **rules** — the model and the *why* (descriptive docs) |
| `workflows/` | the **usage** — how capabilities compose into whole flows (the project-level suite) |
| `ledger/` | the **provenance** — durable audit records; data, outside the node taxonomy |

**Rule-in-design, behavior-in-capability.** A rule and the behavior enacting it live apart: rules go
to `design/` as descriptive docs, the scenarios that enact them go to the capability folders as
behavioral specs, and a reference artifact is homed in the capability that owns it. This keeps
`design/` readable as a model while the capabilities stay testable as behavior.

**Root files, not folders.** Every mandated folder is an exception to screaming architecture, so the
mandated set stays minimal: anything that is one document lives as a **root file beside `spec.md`**.
`glossary.md` — the project's ubiquitous language, every load-bearing term defined once — is
required of every project spec.

**Two levels, never three.** A node is `<capability>/<unit>` and never sits three deep. A
sub-grouping inside a capability is a **cross-cutting concern**, so it is expressed as a `concept:`
tag and recovered through the generated by-concept index — never as a third folder level.

**The concept axis.** The tree can privilege only one axis, and it privileges capability; a concern
enacted across several capabilities is declared in `concept:` frontmatter and navigated through the
index instead.

**Suite organization.** Unit suites **colocate** with their capability node, one per unit. The
project-level suite lives in `workflows/`, where a **workflow** is the project-level analogue of a
use case — a path through the composed capabilities.

## One spec per project

A **project** is the unit a spec maps to — a repo harness, an agent plugin, an npm package, a
website, or one package inside a monorepo. Each has exactly **one** spec: one `spec.md`, one suite,
one gate/freeze baseline. Growth is absorbed by **adding folders**, never by splitting into sibling
specs — splitting fragments the lifecycle, so one change touching three areas would re-open three
frozen specs and pay three approvals.

**Colocate by default**, nested projects included. **Hoist only when the spec cannot be kept out of
what ships** — the project dir is copied **wholesale**, with no include/exclude mechanism to leave
the spec behind. The one identified case is an **agentic plugin**: plugin install copies the whole
directory, so a colocated spec would reach every consumer. An npm package colocates — its `files` /
ignore list excludes the spec from the tarball. **Nesting is never the reason**; if a new packaging
format has the same all-or-nothing copy, it joins the hoisting case.

## Strategy is policy; homes are data

Screaming architecture is the **default**, not the only layout. Whichever layout a project uses is a
**choice**, and choices are declared. But the choices are **not equals** — see the partition stake
below; declaring a layout does not license breaking node<->capability alignment.

- **The strategy** (`capability-first`, `mirror-source`, …) is **declared** in the root `spec.md`
  **placement map** and **read**. Never derive it from the tree: a greenfield project has no tree yet
  and still has a strategy; deriving it from a healthy tree is circular (it launders a past decision
  as an observation); and on a half-migrated tree it perpetuates the layout being migrated *away*
  from.
- **The homes** — which folder a given concept's node sits in — are **facts** about the current tree,
  derived from `concept:` tags. A stored home list is a second source that rots, so homes are never
  stored.
- **They compose:** the declared strategy **parameterizes the derivation**. Keep deriving homes, but
  ask the placement map *which* derivation to run.

**The placement map has two parts, and a placement judgment must consult both.** Beside the declared
strategy it carries a **routing table** — the maintained "a concept of kind K lives in home H"
taxonomy plus the human **tie-break** rows for genuinely contested overlaps. The table records
decisions the strategy alone does not settle, so a node placed by an explicit routing-table row is
**correctly placed even when it does not match the strategy's derivation**. Judging misplacement on
the strategy alone therefore reports false findings against exactly the placements a human already
adjudicated. The test is a disjunction: a node is misplaced only when it **neither** follows the
declared strategy **nor** matches a routing-table row.

This is the same split the corpus-discovery rule already makes — fixed conventions are scanned,
while an off-convention anchor list is declared and curated. "No drift" means *do not store what you
can observe*, never *do not declare a choice*.

### The partition stake — why capability-first is more than a preference

Capability-first is the partition the **mission scheduler** depends on. One mission owns one
spec-node, so when **node <-> capability is 1:1** a change touches one node and its collisions are
legible; missions run in parallel. A **layered / framework-first top level scatters one capability
across many folders** — the mapping breaks, a single behavior smears across nodes, collisions
explode, and the schedule degrades toward **serial** (ADR-0025).

So layouts are ranked by whether they preserve that alignment, not by taste:

- **capability-first** — aligned by construction; the recommendation.
- **mirror-source** — inherits whatever alignment the source has. Best case is a feature-first
  source, which is already capability-aligned; over a layered source it is **still offered**, with
  the cost named (below).
- **layered / framework-first as the *top* level** — **discouraged** as a *chosen* layout for a
  project free to choose, and a declaration does not rescue it. Layering survives *nested inside* a
  capability.

The invariant that holds under **every** strategy: **one capability per node, never smeared across
nodes**. A declared layout says where a node goes; it never licenses a capability to scatter. The
scheduler's **false-conflict rate** is the standing metric of the partition's quality.

### A coarse partition costs precision, not correctness

This is why an imperfect layout is workable rather than disqualifying. The scheduler is
**conservative** — a collision it cannot resolve **serializes** — so the worst case of a poor
partition is a **slower schedule, never a corrupted one**. Three mechanisms recover most of the loss:

- **The collision ladder descends below the node** — file, region, semantic, symbol — so two missions
  sharing a node but touching different symbols classify **soft** and still co-wave. The residue is
  `symbol-rung-deferred`: symbols that cannot be inferred stay hard.
- **Worktrees** dissolve file-level false dependencies until write-back.
- **The concept axis** carries the capability view the folders do not: in a mirrored tree the folders
  name source areas while `concept:` tags still name capabilities.

**Adoption over purity.** Demanding a restructuring before a project may hold its first spec is an
entry toll, and an unadopted tool partitions nothing. A project adopts on the shape it has,
accumulates `concept:` tags as it writes nodes, and **hoists one capability at a time when the
false-conflict rate earns the move** — a concept spanning many nodes being the measured signal that a
capability wants its own home. Capability-first is the **destination**, reached on evidence, not the
entry condition.

## Key points (read-check)

1. **Three kinds, declared** — descriptive / reference (`## Subject`, no suite) / behavioral (owns a
   suite); never inferred from files or location.
2. **Placement is the taxonomy applied to folders** — rules to `design/`, behavior to the capability
   folder, reference artifacts to the capability that owns them.
3. **Screaming architecture** with three non-capability folders (`design/`, `workflows/`, `ledger/`)
   and **root files, not folders**, for single documents (`glossary.md` required).
4. **Two levels, never three** — deeper sub-grouping is a `concept:` tag, not a folder.
5. **One spec per project**; colocate by default and **hoist only when the spec cannot be kept out of
   what ships** (the agentic plugin) — nesting is never the reason.
6. **Strategy is policy, homes are data** — read the declared strategy from the placement map, derive
   homes from `concept:` tags, and let the strategy pick the derivation.