udesign

name	udesign
description	Use before any creative work — features, components, behavior changes. Turns an idea into a validated spec with explicit tradeoffs and unknowns, and splits scope into multiple tasks if it's too large. Output is the `## Design` section of the task file.

Design

Turn an idea into a validated spec through collaborative dialogue. Output lives in docs/tasks/<slug>.md — ## Design, ### Invariants (IV), ### Principles (PC), ### Assumptions (AS), ### Unknowns (UK) — with a TDD decision recorded. Nothing is planned or written until the user approves.

When to invoke

Before any creative work: new features, component builds, behavior changes, architectural moves. Even "simple" tasks — five minutes of design prevents hours of rework. Skip only when the task is trivial (typo, one-line fix) and the user has confirmed the skip.

Process

Follow these steps in order. Do not combine or skip.

1. Explore project context — files, recent commits, existing patterns. No exceptions.
2. Scope check — split into multiple tasks now if the ask is too large.
3. Ask clarifying questions, one at a time. Prefer multiple choice.
4. Propose 2–3 approaches. Each with explicit tradeoffs and unknowns.
5. Backwards-compat check — flag anything that could break already-running or already-used systems. Ask the user how to resolve before proceeding.
6. Present the design in sections. Get per-section approval.
7. Identify invariants (IV), principles (PC), assumptions (AS), and unknowns (UK).
8. Decide TDD — yes or no, with reason. Use test-driven-development's applicability rule.
9. Write to task file — ## Design, ### Invariants, ### Principles, ### Assumptions, ### Unknowns.
10. Self-review for placeholders, contradictions, scope, ambiguity. Fix inline.
11. Wait for user approval before invoking uplan.

Scope check — split before planning

If the ask spans multiple independent subsystems, stop and propose a split. Each piece gets its own task file. We work on one in this dialogue; the rest wait.

User: "Add auth, billing, and admin dashboard."

Agent: "That's three independent tasks. I'd split into:

• docs/tasks/add-auth.md
• docs/tasks/add-billing.md
• docs/tasks/add-admin-dashboard.md

Each is a separate task file, designed and built in its own session. Which one should we start with?"

Agent designs all three at once in a single task file. Later agents can't resume a coherent piece of work; plans become gigantic and unreviewable.

A good test: can a plan for this piece produce working, testable software on its own? If no, it's too big.

Proposing approaches — tradeoffs and unknowns, always

For every option, state:

• What it is: 1-2 sentences
• Tradeoffs: what you gain, what you give up (cost, complexity, flexibility, reversibility)
• Unknowns: what you can't answer without more info or experiment

End with a recommendation and why. Don't hedge on the recommendation — if the tradeoffs don't settle it cleanly, say that explicitly and ask the user to weigh in.

"Option A: Redis-backed rate limiter. - Tradeoff: fast, durable across restarts. Adds Redis as a required dep in prod. - Unknown: our existing Redis cluster's latency from the edge nodes — need to measure before committing.

Option B: In-memory token bucket per pod.

• Tradeoff: zero new infra, simpler code. Loses limits on pod restart; uneven limits across horizontally-scaled pods.
• Unknown: how often pods cycle — if it's every 10 minutes, users see limit resets.

Option C: Postgres-backed counter with short TTL.

• Tradeoff: uses existing DB; no new infra. DB write per request is expensive at our RPS.
• Unknown: whether our DB can absorb the extra write load — need a napkin calc.

Recommendation: B for now, revisit when we outgrow it. The redis latency unknown (A) and write-load unknown (C) both need measurement work before committing, and B is cheap to replace."

Backwards compatibility — flag breaks loudly

Before presenting the design, enumerate anything in the chosen approach that could break a system already in use: API shape changes, schema migrations, renamed config keys, removed commands, on-disk format changes, changes to outputs that other code/tools consume, behavioral changes to stable endpoints. Surface each one with its blast radius and ask the user how to resolve: deprecate with shim, hard break with migration, version the new behavior, or revise the approach. "Backwards-compat risks: - `GET /api/v1/users` response shape changes — field `name` splits into `first_name`/`last_name`. Any existing client expecting `name` breaks. Options: (a) return both until v2, (b) hard-break with a migration note, (c) ship as `/api/v2/users` and leave v1 alone. Which? - Config key `log_level` renamed to `logging.level`. Running deployments on old configs will silently fall through to the default. Options: (a) read both for one release, warn on old, (b) fail loud on old key. Which?" Agent designs a schema change without flagging it. Execute runs the migration. Production service that still reads the old column 500s. Root cause: design never surfaced the break.

If the task is greenfield (no existing consumers), say so in one line and move on. Don't invent risks.

ID conventions — define once, reference by ID

Entities in the task file are assigned short IDs so later sections (Plan, Verify, Conclusion) can reference them without re-quoting full sentences.

Design owns four entity types:

• IV1, IV2, … — Invariants
• PC1, PC2, … — Principles
• AS1, AS2, … — Assumptions
• UK1, UK2, … — Unknowns

Rules:

• Defined once with a full sentence at first appearance; later mentions are ID-only.
• Max one sentence per definition.
• Numbering is scoped to the task file. The same ID can recur across tasks with different meanings.
• IDs are for persisted artifacts (task file, commit messages, agent-to-agent prompts). When talking to the user in chat, expand the ID — write out the invariant, principle, or assumption in plain English. "IV3 was violated" is fine in the task file; to the user say "the invariant that Dataset must not import from training/ was violated". Mentioning the ID alongside is OK; replacing the content with just the ID is not.

Plan owns PH (phases) and RK (risks). Verify owns CK (checks). Those are introduced in their stage's skill.

Identifying invariants, principles, assumptions, unknowns

IV — specific things that must hold. Concrete enough to check against the code. - IV1 — The `Dataset` class must not import from `training/`. - IV2 — All DB writes go through the `transaction()` helper. PC — softer abstract guidance. Still concrete enough to audit. Task-specific only — the Global Principles (GPC1–GPC8) in `.opencode/references/principles.md` (or `~/.config/opencode/references/principles.md` for global installs) apply everywhere and don't need to be restated. List a PC only when the task deviates from a GPC (name which one and why) or when it needs an extra rule the GPCs don't cover. - PC1 — Fail fast, no silent fallbacks. - PC2 — Prefer composition over inheritance. AS — unverified premises the design rests on. Conclusion must report whether each held. - AS1 — The upstream `users` service returns `email` as UTF-8 in every response. - AS2 — Nightly batch volume stays under 10M rows for the next quarter. UK — open questions the design cannot answer alone. Resolved during plan, execute, or explicitly deferred. Conclusion must report outcome. - UK1 — Whether the existing Redis cluster has spare capacity for this workload. - UK2 — Exact failure mode when the upstream API rate-limits mid-batch.

Not principles: "prefer composition" (too vague without "over inheritance"). "Be consistent." "Write clean code."

Assumptions vs invariants: an IV is something the code guarantees. An AS is something the world is assumed to give you. If the code can enforce it, it's an IV; if it depends on something outside your control, it's an AS.

TDD decision

Invoke the applicability rule from test-driven-development. Record in Design:

TDD: yes

or

TDD: no (reason: one-off migration script; no reusable logic)

Task-file output shape

## Design
<purpose, scope, chosen approach, key decisions, tradeoffs that settled it>
<TDD: yes|no (reason)>

### Invariants
- IV1 — <specific thing that must hold>
- IV2 — <...>

### Principles
- PC1 — <softer guidance — concrete enough to check>
- PC2 — <...>

### Assumptions
- AS1 — <unverified premise the design rests on>
- AS2 — <...>

### Unknowns
- UK1 — <open question left to plan / execute>
- UK2 — <...>

Rules

• One question per message. No batching. (Hands-off: ask only when genuinely blocking; prefer conservative defaults logged in the task file.)
• YAGNI ruthlessly. Cut anything not needed for the stated goal.
• Follow existing patterns. Targeted improvements only if they serve this task.
• Isolation. Units with one clear purpose; interfaces understandable without reading internals.
• No code yet. Design's output is words, not code.
• Omit empty subsections. ### Invariants, ### Principles, ### Assumptions, ### Unknowns are pre-seeded by the /make template. Delete any that end up with no entries — never leave a placeholder like <empty>, "none", or "n/a". See _brevity.md principle 1.

Hands-off mode

See handsoff for the full contract. Stage-specific delta: Design is still the one interactive stage — run the full process. The only relaxation is "one question per message" → "ask only when genuinely blocking; prefer a conservative default". Log each defaulted answer as - udesign: <what> — <rationale> in ### Hands-off decisions; log no-default gaps under ### Deferred (needs user input).

Terminal state

User has approved the Design section (interactive) or the Design has been written and self-reviewed (hands-off) → invoke uplan. Do not write code. Do not invoke any other skill.