design-preview

name	design-preview
description	Preview the planned design for a scenario before writing tests. Shows domain model changes, usecase patterns, and key design choices. Use before red-usecase to get user approval on the implementation approach. If the user rejects the design, offers to discuss inline or escalate to /architecture for a full ADR.

/design-preview - Scenario Design Preview

Usage

/design-preview 10 "Filter by date range"    # Story 10, named scenario
/design-preview 10 9                          # Story 10, scenario 9
/design-preview                               # Detect from progress.md

Purpose

Before writing any test code, present the planned implementation design to the user for approval. This catches design disagreements early — before red-usecase locks in the approach.

This is also the reuse gate for a scenario invented mid-cycle (see .claude/guidelines/workflow-detail.md "Net-New Scenarios Introduced Mid-Cycle"): a scenario not traceable to a scanned tests/* scenario must pass through here so step 2a scans its hazards before its red phase locks.

Workflow

1. Gather Context

1. Read the story spec — full story document for business context, requirements, constraints, business rules
2. Read the scenario from tests/01_API_Tests.md
3. Read ProductSpecification/ExpectedLoad.txt — for scale assumptions (use real numbers, never guess)
4. Read existing code — domain entities, usecases, ports, request/response DTOs
5. Read ADRs — check decisions/*-decision.md files in the story directory that may constrain the design
6. Read the acceptance test (if red-acceptance is done) — understand expected API behavior

2. Generate Options

Think through 2-3 viable approaches. For each option, capture:

• Summary — one line describing the approach (domain changes, ports, sequence)
• Pros — 2-3 bullets
• Cons — 2-3 bullets

Mark one option as Recommended with a one-line rationale ("why this over the others"). For trivial scenarios (validation, error handling, mechanical CRUD) where alternatives would be contrived, present a single option labelled "Only viable approach" instead of forcing artificial alternatives.

2a. Hazard Catalogue Scan (before presenting)

Before presenting the options, scan the drafted design against the hazard catalogue — the spec-time, closed-list complement to the open-ended commit-time review passes. Per .claude/guidelines/hazard-catalogue/_index.md (read its "How to apply it"), fan out one hazard-scan-agent per group in the index's Groups list — iterate that list, never a hand-copied set, or a newly-added group goes unchecked — each carrying the drafted design, _index.md, and its one group file; dispatch them concurrently, collect each pass's GAPs and seam flags, then run one synthesis pass (per _index.md's "Reason across the seams") over the index-named seams and every flagged seam. Fold every GAP back into the design before presenting: the option the user approves must already carry the forced guard (a domain method, a port contract, a specific check), not a vague mitigation. Do not proceed to step 3 with an open GAP — a hazard the design can't yet guard is a reason to widen the options or escalate to /architecture, not to present anyway. Groups whose triggers can't fire at this usecase altitude — the client/frontend group above all — are dismissed as a block with one explicit "out of altitude here" line (per _index.md's "A dead group is dismissed as a block"), never silently passed. When you present, surface the scan outcome — the group set scanned, each fired-trigger GAP, and the guard the chosen option carries for it — so the user approves a design whose hazards are visible, not hidden.

3. Present Options

Show each option as a labelled block: title, summary, pros, cons. Include the recommendation rationale below the recommended option.

Simple scenarios: each option in 3-5 lines. Complex scenarios: each option with method signatures/pseudocode, domain model changes, pipeline/sequence diagrams, port changes.

4. Get Option Choice

Ask with AskUserQuestion:

• First answer = the recommended option, label suffixed with "(Recommended)"
• Other answers = alternative options (one per non-recommended option, up to 3 alternatives)
• Last answer = "Reject all — escalate to /architecture"

Option labels must fit in a chip (12 chars). Keep answer descriptions to one short line.

If user rejects all → invoke /architecture and STOP. Do not proceed to the ADR question.

5. Get ADR Decision

After an option is chosen, ask separately with AskUserQuestion whether to capture the decision as an ADR:

• "Write ADR" — recommended when the user picked a non-recommended option, when the trade-offs are non-obvious, or when downstream scenarios will likely revisit the choice
• "Skip ADR" — recommended for trivial scenarios (single-option flow) or mechanical choices with no real trade-off

Pick which option to mark "(Recommended)" based on the choice the user just made in step 4.

6. Completion

Outcome	Action
Option chosen, no ADR	Mark design step as [x]. No files created.
Option chosen, write ADR	Mark design step as [x], then write an ADR using .claude/templates/spec/adr-format.md to the story's decisions/ subfolder. Pre-populate the ADR's "Rejected" table with the un-chosen options from step 3. Commit includes the ADR file.
Rejected all → /architecture	Do NOT mark design. /architecture runs and decides the ADR. Mark design only after the ADR lands.

Rules

• Never write code — this is a design step
• Never create files — design lives in the conversation (unless escalated to /architecture)
• Keep it concise — the goal is alignment, not a design document
• If trivially similar to a previous scenario, say so and ask to approve
• Scope of progress.md changes: design-preview may ONLY mark the design checkbox as [x]. It must NOT modify, skip, or rewrite any other steps (usecase, adapter, green-acceptance). Skip recommendations go in the design output text only — /continue applies approved skips to progress.md after the design work unit completes, validating each skip against the "zero production files modified" rule in .claude/guidelines/tdd-rules.md.