Phase Preview

One design in, one screen per phase out. Each phase file shows everything available by that phase and nothing that isn't, in exactly the positions the approved design already put them — so a phase screen is the real build target for that release, not a redrawing of it. Nothing here is drawn: this is the approved design with the later releases taken out, which is why it can be checked mechanically rather than by eye.

base.html ──┬──► phase-1/base.html    only what ships in phase 1
            ├──► phase-2/base.html    phase 1 + phase 2
            └──► phase-3/base.html    phase 1 + 2 + 3   ( = the base, if phases cover it all )

Subtract only. Nothing is moved, resized, restyled or repositioned; nothing new is invented. That is the entire discipline of this skill, and §4 proves it mechanically rather than trusting the eye.

1 · Resolve the two inputs

The base wireframe — one self-contained HTML file. If the user hasn't named one, ask; don't guess among the files in design/. Never work from an already-phased file: every phase is cut from the original.

The phases, and what belongs to each. In priority order:

1. A story map (*.json from /vstack:user-story-map) — phases[] gives the order and goals, stories[] give what lands when. This is the best input; ask for one if a story map exists.
2. A spec with P1/P2/P3 priorities, or a roadmap.
3. The user tells you the phases in the conversation.

If none of those exist, stop and ask — inventing a release plan is not this skill's job.

2 · Write the phase plan before touching any HTML

Open the base and inventory every element, component and interaction in it. Assign each one the earliest phase it exists in. Write that out and show the user before generating anything:

| Element | Earliest phase | Why |
|---|---|---|
| Candidate table + search | 1 | "Search candidates by name" |
| Bulk-select toolbar | 2 | "Move several candidates at once" |
| "Ask AI" button + drawer | 3 | "Summarise a candidate with AI" |
| Export button | — | not in any story — flag it |

This step is the one that makes the rest mechanical. Doing it up front means each phase is a lookup rather than a fresh judgement call, and it surfaces the two things worth a conversation:

• Elements no story covers. Say so rather than silently keeping or cutting them. Chrome that every phase needs (nav, page title, empty states) is phase 1 by default — call that out too.
• Phase-1 features gated behind later ones. These need the skeleton rule in §3; find them now, not mid-edit.

Confirm the plan, then generate. If the user re-slices the story map afterwards, come back here.

3 · Generate the phases, one at a time, in order

For each phase 1, 2, 3 … in order, and only starting the next once the current one is written, checked and shown:

1. Start from the original full wireframe. Never from the previous phase's output — errors compound.
2. Subtract every element, component and interaction that does not belong to the current phase or any earlier phase. Phases are cumulative: phase 2 shows phase 1 and phase 2.
3. Keep the exact same layout, spacing, alignment, sizes and visual hierarchy. Do not move, resize, restyle or reposition any remaining element. Leave the stylesheet exactly as it is — rules that no longer match anything are fine and expected.
4. Fully implement the features available in this phase (and earlier). What survives still works; a control that can't act is removed, not left dead.
5. A current-phase feature gated behind a later-phase one stays in its original place, and the later-phase gate is replaced with the absolute minimum skeleton — an empty container, a disabled placeholder, or a plain frame — so the current-phase feature stays visible and reachable. Every skeleton element carries data-phase-skeleton, which is what lets §4 tell an allowed placeholder apart from an invented element.
6. Do not invent new elements or redesign anything. Only subtract.

Write each to <dir>/phase-<n>/<name>.html — the sibling layout /vstack:review and the Cavalry design/ convention both expect — and suffix the <title> with — Phase <n> so the file names itself wherever it's opened.

The last phase usually equals the base. When the plan leaves nothing to subtract, say so and point at the base file instead of writing a duplicate.

4 · Prove each phase is a subtraction

Before showing a phase, run it:

SKILL=<this skill dir>
node "$SKILL/assets/check-subtraction.mjs" --base design/app.html --phase design/phase-1/app.html

It prints how much was removed and exits non-zero on any violation. Fix the file and re-run until it passes — don't explain a failure away, and don't show the user a phase that hasn't passed. It doesn't read copy or data, so still diff the file yourself for changed text.

--json gives the same result as an object.

5 · Review each phase

A phase file is a design the user should be able to argue with. Hand each one to /vstack:review — it opens the page in the review workspace, takes comments straight on it, and publishes the next version. Review phase N and settle it before generating phase N+1; a comment on phase 1 usually changes the plan for every later phase.

Comments that amount to "this belongs in a different phase" are a §2 change, not an edit: update the plan, then regenerate the affected phases from the base.

6 · Put them on a scrubber

Files one at a time answer "what does phase 2 look like?". The question people actually ask is "what does this screen become, release by release?" — which is one control:

SKILL=<this skill dir>
node "$SKILL/assets/phase-view.mjs" --dir design --name candidate-pipeline \
  --labels phases.json          # optional: { "1": { "label": …, "goal": … } }

It writes <name>-phases.html — one self-contained file, the review workspace running in phase mode: same chrome, same browser window, the rail showing releases instead of versions. Drag along it and the screen fills in. Highlight new outlines what the phase in view adds over the one before it.

Give the labels if you have them — a story map's phases[] already carries the name and goal, and P2 · Move people in bulk · a dozen at a time after a screening day says more than Phase 2.

The per-phase files stay the source of truth. They are what the build stages consume; this is a way of looking at them, generated from them, and safe to delete and rebuild.

It is view-only, and that is deliberate — no annotate, no comments, no Send. Moving a feature between phases is a re-slice of the story map, not an edit of this page, and nobody has designed what editing here would mean. A viewer that can't lie beats an editor that edits the wrong file. Review happens on the phase files themselves, through §5.

Notes

• Self-contained, like the base. No external fonts, stylesheets or scripts — the phase files get opened, reviewed and bundled exactly as the base does.
• Interactions count as elements. A filter that only works because of a phase-3 index, a button that opens a phase-2 modal — these are subtracted too, even when the markup looks phase-1.
• Don't delete the CSS for what you removed. Unused rules are harmless, and editing the stylesheet is the fastest way to fail §4 and to drift the design.
• data-phase-skeleton is a real marker, not a comment. It stays in the file: it tells the checker what to allow, and tells a reviewer that the empty frame is deliberate.
• Highlight new is a heuristic, and says so. It matches elements between two phases by tag, id, classes and their own text, because subtraction leaves a surviving element textually intact. Two identical buttons read as one; an element whose text changed reads as new. Both are wrong on the page, in front of you, which is the right place for a wrong answer to show up.

State & handoff

No .vstack/pipeline.json? You're standalone — a base wireframe and a set of phases are all this needs, and that is a first-class way to run it. Skip this section, and never create the state file: only /vstack:start and /vstack:requirements bring a pipeline into being.

With a state file:

• Read specs/story-map.json for the phases — their order, names and goals, and which stories land when. artifacts.wireframes[] for the base page. While a story map exists it is the phase truth; don't re-derive phases from anything else.
• Write artifacts.wireframes[].phases — the per-phase files, against the wireframe they were cut from — plus stage: "phase-preview" and a history entry. The generated <name>-phases.html (§6) is a view, not an artifact: don't record it, and don't let a later stage read it.
• Next — /vstack:phase-build plans and builds phase 1. Offer to run it; don't ask whether to continue.