Scaffold Invariants

Scaffold Invariants — Project-Specific Skill Bootstrap

Specialized skill scaffolder. Produces a project-specific invariants skill (<project>:design-invariants by convention) that pairs with axiom:design via the pairing contract.

Triggers

Use when:

• Starting a new project that needs its own architectural invariants formalized
• Migrating from a verbal "we always do X" rule to a documented, testable invariant
• Establishing the project-specific half of an axiom:design pairing for the first time

Do NOT use when:

• Updating an existing invariants skill — edit it directly.
• Authoring a generic skill — use Anthropic's skill-creator (or its vendored copy if installed) for unconstrained skill creation.

Interview

Five categories of questions, asked one at a time. The output of each shapes the generated skill.

1. One-line characterization

"If you had to describe this project's runtime in one sentence, what would it be?"

The answer becomes the skill's framing line. Example from Exarchos: "a single-machine event-sourced process manager with cooperative agents." This sentence governs every downstream invariant — if a candidate INV doesn't follow from this characterization, it doesn't belong.

2. Non-obvious commitments

"What architectural decisions has this project committed to that aren't obvious from reading the code?"

Each answer is an INV-N candidate. Examples: "the event store is the source of truth, never state files", "all phase transitions go through one HSM module", "no MCP-second-class assumptions in any design". Aim for 3–7 invariants — fewer feels under-codified, more becomes hard to remember.

3. Dimension overlap

For each candidate INV, ask:

"Which of axiom's dimensions (DIM-1 Topology / DIM-2 Observability / DIM-3 Contracts / DIM-4 Test Fidelity / DIM-5 Hygiene / DIM-6 Architecture / DIM-7 Resilience / DIM-8 Prose) does this specialize?"

The answer seeds the axiom_overlap: DIM-N field. An INV may overlap zero, one, or multiple dimensions. Zero means it's project-specific without a generic counterpart — valid but rarer.

4. Failure mode

For each candidate INV, ask:

"What's the failure mode if this is violated? What does the system look like when this rule breaks?"

The answer seeds the severity guide. Map: catastrophic / data-loss / silent corruption → HIGH; misleading / hard to debug → MEDIUM; cosmetic / mild → LOW.

5. Mechanical checks

For each candidate INV, ask:

"Is there a mechanical way to detect a violation — a grep pattern, lint rule, type check, or static analysis?"

The answer seeds references/deterministic-checks.md. If no mechanical check exists, that's fine — record "reasoning-driven; no automated check" so the human reviewer knows.

Emit

After the interview completes, emit the project-specific skill structure. Default output path: .claude/skills/<project>-design-invariants/.

Files emitted:

• SKILL.md — frontmatter + body. Frontmatter includes pairs-with: axiom:design. Body lists the invariants with their severities, axiom-overlap declarations, and links to per-INV reference files.
• references/INV-N-<slug>.md per invariant — one file per INV. Each file contains: framing, acceptance questions, repo-grounded checks, severity guide, worked example (violation + fix). Modeled on exarchos/.claude/skills/design-invariants/references/INV-1-event-sourcing.md.
• references/deterministic-checks.md — the grep / structural / lint patterns, organized by INV-N. Modeled on exarchos/.claude/skills/design-invariants/references/deterministic-checks.md.

Templates live at templates/ in this skill's directory:

• templates/SKILL.template.md
• templates/INV.template.md
• templates/deterministic-checks.template.md

Each template uses {{TOKEN}} placeholders that are filled from interview answers.

Emit-correctness properties

The generated skill must be well-formed:

• Generated SKILL.md declares pairs-with: axiom:design in frontmatter (so axiom:design discovers it).
• Each invariant entry declares axiom_overlap: DIM-N if the user named one in the interview (Q3); omits the field otherwise.
• Generated structure mirrors exarchos:design-invariants exactly: SKILL.md + references/INV-N-<slug>.md per invariant + references/deterministic-checks.md.

Failure Modes

• Vendored skill-creator missing or stale (vendor/skill-creator/UPSTREAM.md older than 30 days, or vendor/skill-creator/ directory absent) → fall back to bundled templates only (no description tuning, no eval-prompt suggestions). Emit a one-line warning: Vendored skill-creator not available; emitted scaffold uses bundled templates only. Sync vendor and re-run for description tuning.
• Output directory already exists with content → prompt before overwriting; default action is abort.
• Interview yields zero invariants → emit a SKILL.md with empty INV section and a one-line note: No invariants surfaced from interview. Re-run when project commitments are clearer.

References

• Pairing contract: @skills/backend-quality/references/pairing-contract.md
• Project archetype: exarchos/.claude/skills/design-invariants/SKILL.md
• Vendored upstream tooling: vendor/skill-creator/SKILL.md (full directory copy from anthropics/skills; reference only, not loaded as a triggerable skill)