diff --git a/.claude/skills/alignment/SKILL.md b/.claude/skills/alignment/SKILL.md
index 5762984..aa57ebd 100644
--- a/.claude/skills/alignment/SKILL.md
+++ b/.claude/skills/alignment/SKILL.md
@@ -55,6 +55,17 @@ Review all changes in scope. If changes span multiple patterns below, apply all
 5. **Styles and UI**: When altering CSS or layout, follow or generalize existing patterns
    (CSS Modules + design tokens in `styles/tokens.css`) rather than writing from scratch. Don't
    fix whitespace/formatting (trailing newlines etc.) — Prettier owns that.
+   - **Control primitives & the two-height scale** (arch 09 §4): action buttons are the
+     `Button` component, icon-only buttons are `IconButton` — never a freshly styled
+     `<button>`. Interactive controls are `var(--control-height)` (32px) or
+     `var(--control-height-lg)` (40px); a hardcoded control height (28px, 36px, …) in a
+     diff is a finding. A freshly written bordered-field recipe is the same finding —
+     fields share one look (1px `--border-strong`, `--bg` fill, `--control-height`); a
+     new input should copy an existing field class, not re-derive it. Call-site classes composed onto a primitive may only do layout
+     (flex, margins, reveal) or a documented state accent (outlined-danger, pressed) —
+     restyling the primitive's box from a call site is a finding. Borders mark function:
+     value-holding controls get `--border-strong` boxes; plain actions are ghost or
+     filled; list rows are flat with dividers, not stacked boxes.
 
 6. **Code Comments**: Comments should not duplicate what the code already says. Remove
    parroting comments. Ensure comments capture non-obvious _why_ — design decisions,
diff --git a/docs/architecture/09-visual-design.md b/docs/architecture/09-visual-design.md
index ab0826d..07a633d 100644
--- a/docs/architecture/09-visual-design.md
+++ b/docs/architecture/09-visual-design.md
@@ -149,11 +149,43 @@ UI by swapping one set of values. Borrowed from Carbon's layering model:
 
 ## 4. Component conventions
 
-- **Buttons:** square, 32px (compact) / 40px (default) tall. Variants: **primary**
-  (filled `--accent`), **secondary** (bordered), **ghost** (text-only, borderless),
-  **soft-accent** (ghost on an `--accent-soft` wash — a low-emphasis solicitation,
-  e.g. Donate), **danger** (filled `--support-error`). 600-weight label. Clear
-  hover/active and a visible focus ring.
+- **The control scale (two heights, enforced by tokens + primitives).** Every
+  interactive control is `--control-height` (32px) or `--control-height-lg`
+  (40px) — tokens.css. 32px is THE control height: buttons, fields, selects,
+  segmented controls, icon buttons, anything in a toolbar, form row, or dialog
+  action row. 40px is reserved for standalone primary CTAs (the library's Build
+  Chart, a modal list-pane's New X) and modal footers. A third height is drift —
+  the pre-token codebase accumulated 26/28/30/36/42px variants one component at a
+  time, which read as "shaky" the moment controls shared a row. The rule is
+  enforced mechanically: action buttons are the **`Button`** primitive, icon-only
+  buttons are **`IconButton`** (24px `sm` exists solely for controls nested
+  _inside_ a 32px control — a search field's clear, a toast's dismiss); writing
+  `height:` on a new ad-hoc button is the code smell.
+- **Buttons:** square, via the `Button` primitive. Variants: **primary** (filled
+  `--accent`), **secondary** (1px `--border-strong`, `--bg` fill — the same
+  field-on-layer treatment as inputs, so a bordered control on a gray panel goes
+  white, never a darker gray), **ghost** (text-only, borderless; a transparent
+  border holds the box size), **soft-accent** (ghost on an `--accent-soft` wash —
+  a low-emphasis solicitation, e.g. Donate), **danger** (filled
+  `--support-error` — the confirm step), **danger-outline** (secondary geometry,
+  red label, filling solid red on hover/focus — a destructive action sitting
+  among peers, e.g. a detail view's Delete). 13px 600-weight label. Clear hover/active and a visible
+  focus ring. **Inline link-style actions are a separate kind, not a Button
+  variant**: small accent-text actions embedded in content ("+ Add filter",
+  "Swap X/Y", "Use a constant", a popover's Reset) deliberately sit below the
+  control scale — content-sized, 11–12px, no box — so they read as part of the
+  prose/panel they act on, not as toolbar controls. Don't "promote" them to
+  Buttons; their smallness is the emphasis level.
+- **Borders mark function, not decoration.** A 1px `--border-strong` box belongs
+  to things that _hold or receive a value_: fields, selects/disclosure triggers,
+  segmented controls, secondary buttons, drop targets (dashed). Plain actions are
+  ghost or filled — never outlined boxes. List rows are flat (hairline dividers +
+  hover fill), not stacked boxes. With square chrome, every box makes alignment
+  errors visible, so each border must earn its place; when a region looks
+  "busy", remove boxes before shrinking anything. (Carbon goes further — fields
+  are bottom-border-only and its secondary button is a gray fill; our fully-boxed
+  fields are a recorded divergence, §2, which is exactly why box discipline
+  matters more here, not less.)
 - **Emphasis hierarchy (Carbon button/usage).** A region carries **one**
   high-emphasis (primary) button at most; everything else is lower emphasis. In
   toolbars/headers full of utilities, the utilities go **ghost** so they recede
@@ -168,8 +200,11 @@ UI by swapping one set of values. Borrowed from Carbon's layering model:
   fill one elevation step above their surface** — on `--bg` → `--layer-01`, on a
   `--layer-01` surface (dialogs, panels) → `--layer-02`. Filling to the _same_
   layer as the surface reads as no hover at all (the collision that left the
-  confirm dialog's Cancel looking dead). Any button placed on an elevated surface
-  must step its hover fill up to match.
+  confirm dialog's Cancel looking dead). The step is mechanical: Button/IconButton
+  hover with `var(--control-hover-fill, var(--layer-01))`, and an elevated surface
+  sets `--control-hover-fill: var(--layer-02)` once on its container (the header,
+  the modal chrome, the confirm card, the library's metadata panel) — controls
+  inherit the right step instead of each re-encoding it.
 - **Focus ring:** a 2px `--focus` outline (offset 1–2px). Always visible on
   keyboard focus — accessibility is non-negotiable (principle 4).
 - **Fields** (text, textarea, select, search): square, 1px `--border-strong`,
@@ -411,13 +446,14 @@ The chart `Config` is themed to match the app, per theme:
 
 ## 7. Implementation map
 
-| Artifact                                         | Role                                                  |
-| ------------------------------------------------ | ----------------------------------------------------- |
-| [`visual-specimen.html`](./visual-specimen.html) | Living preview + token sandbox. Iterate here first    |
-| `styles/tokens.css`                              | The settled tokens — ported from the specimen in M1.5 |
-| `styles/base.css`                                | Font wiring (`@fontsource`), reset, reduced-motion    |
-| component `*.module.css`                         | Consume tokens only; no raw hexes, no hardcoded hue   |
-| `src/core/vega-themes.ts`                        | Chart `Config` per theme; categorical palettes        |
+| Artifact                                           | Role                                                                 |
+| -------------------------------------------------- | -------------------------------------------------------------------- |
+| [`visual-specimen.html`](./visual-specimen.html)   | Living preview + token sandbox. Iterate here first                   |
+| `styles/tokens.css`                                | The settled tokens — ported from the specimen in M1.5                |
+| `styles/base.css`                                  | Font wiring (`@fontsource`), reset, reduced-motion                   |
+| `src/app/components/Button.tsx` / `IconButton.tsx` | The shared control primitives (§4) — every action / icon-only button |
+| component `*.module.css`                           | Consume tokens only; no raw hexes, no hardcoded hue                  |
+| `src/core/vega-themes.ts`                          | Chart `Config` per theme; categorical palettes                       |
 
 **Order of work:** settle the specimen → port tokens to `tokens.css` → self-host
 Plex in `base.css` → restyle existing M1 components against the tokens → align
diff --git a/docs/architecture/visual-specimen.html b/docs/architecture/visual-specimen.html
index a637406..229e3fa 100644
--- a/docs/architecture/visual-specimen.html
+++ b/docs/architecture/visual-specimen.html
@@ -44,6 +44,12 @@
         --radius: 0px;
         --border-width: 1px;
 
+        /* Control scale — every interactive control is one of exactly two
+           heights (arch 09 §4): 32px standard, 40px for standalone primary
+           CTAs and modal footers. */
+        --control-height: 32px;
+        --control-height-lg: 40px;
+
         /* Motion — productive only */
         --dur-fast: 70ms;
         --dur-fast-2: 110ms;
@@ -399,26 +405,25 @@
         padding: var(--space-5);
       }
 
-      /* ----- Buttons ----- */
+      /* ----- Buttons (mirrors src/app/components/Button.module.css) ----- */
       .btn {
         font: inherit;
         font-weight: 600;
-        font-size: 14px;
+        font-size: 13px;
         cursor: pointer;
         display: inline-flex;
         align-items: center;
-        gap: var(--space-3);
-        height: 40px;
-        padding: 0 var(--space-5);
+        gap: var(--space-2);
+        height: var(--control-height);
+        padding: 0 var(--space-3);
         border: var(--border-width) solid transparent;
         border-radius: var(--radius);
         transition:
           background var(--dur-fast) var(--ease),
           border-color var(--dur-fast) var(--ease);
       }
-      .btn.sm {
-        height: 32px;
-        font-size: 13px;
+      .btn.lg {
+        height: var(--control-height-lg);
         padding: 0 var(--space-4);
       }
       .btn-primary {
@@ -429,7 +434,7 @@
         background: var(--accent-hover);
       }
       .btn-secondary {
-        background: transparent;
+        background: var(--bg);
         color: var(--text);
         border-color: var(--border-strong);
       }
@@ -947,7 +952,7 @@
 
       <!-- BUTTONS -->
       <section>
-        <h2>Buttons — square, 600 weight</h2>
+        <h2>Buttons — square, 600 weight, 32px standard / 40px lg</h2>
         <div class="row">
           <button class="btn btn-primary">Create snippet</button>
           <button class="btn btn-secondary">Duplicate</button>
@@ -956,9 +961,8 @@
           <button class="btn btn-primary" disabled>Disabled</button>
         </div>
         <div class="row" style="margin-top: var(--space-5)">
-          <button class="btn btn-primary sm">Compact</button>
-          <button class="btn btn-secondary sm">Compact</button>
-          <button class="btn btn-ghost sm">Compact</button>
+          <button class="btn btn-primary lg">Build Chart</button>
+          <button class="btn btn-secondary lg">Cancel</button>
         </div>
         <p class="cap" style="margin-top: var(--space-4)">
           Tab through to see the focus ring (2px accent outline).
@@ -972,7 +976,7 @@
           emphasis.)
         </p>
         <div class="row" style="align-items: center">
-          <button class="btn btn-ghost-util sm">
+          <button class="btn btn-ghost-util">
             <svg width="16" height="16" viewBox="0 0 32 32" style="fill: currentColor">
               <rect x="8" y="18" width="4" height="2" />
               <rect x="14" y="18" width="4" height="2" />
@@ -985,19 +989,19 @@
               /></svg
             >Datasets
           </button>
-          <button class="btn btn-ghost-util sm">
+          <button class="btn btn-ghost-util">
             <svg width="16" height="16" viewBox="0 0 32 32" style="fill: currentColor">
               <path d="M26,24v4H6V24H4v4a2,2,0,0,0,2,2H26a2,2,0,0,0,2-2V24Z" />
               <path d="M6,12l1.41,1.41L15,5.83V24h2V5.83l7.59,7.59L26,12,16,2Z" /></svg
             >Import
           </button>
-          <button class="btn btn-ghost-util sm">
+          <button class="btn btn-ghost-util">
             <svg width="16" height="16" viewBox="0 0 32 32" style="fill: currentColor">
               <path d="M26,24v4H6V24H4v4a2,2,0,0,0,2,2H26a2,2,0,0,0,2-2V24Z" />
               <path d="M26,14l-1.41-1.41L17,20.17V2H15V20.17l-7.59-7.58L6,14l10,10Z" /></svg
             >Export
           </button>
-          <button class="btn btn-ghost-util sm">
+          <button class="btn btn-ghost-util">
             <svg width="16" height="16" viewBox="0 0 32 32" style="fill: currentColor">
               <path d="M17,22V14H13v2h2v6H12v2h8V22Z" />
               <path d="M16,8a1.5,1.5,0,1,0,1.5,1.5A1.5,1.5,0,0,0,16,8Z" />
@@ -1007,7 +1011,7 @@
             >About
           </button>
           <span class="hdr-divider"></span>
-          <button class="btn btn-soft sm">Donate</button>
+          <button class="btn btn-soft">Donate</button>
         </div>
       </section>
 
@@ -1495,8 +1499,8 @@
               ><span><span class="dot draft"></span> Draft changes</span>
             </div>
             <div class="row" style="margin-top: var(--space-5)">
-              <button class="btn btn-primary sm">Publish</button>
-              <button class="btn btn-ghost sm">Revert</button>
+              <button class="btn btn-primary">Publish</button>
+              <button class="btn btn-ghost">Revert</button>
             </div>
           </div>
         </div>
@@ -1611,7 +1615,7 @@
           <div class="motion-box"></div>
         </div>
         <div class="row" style="margin-top: var(--space-5)">
-          <button class="btn btn-secondary sm" id="motionBtn">Play transition</button>
+          <button class="btn btn-secondary" id="motionBtn">Play transition</button>
           <span class="cap"
             >Neutralized automatically under <code>prefers-reduced-motion</code>.</span
           >
diff --git a/src/app/App.module.css b/src/app/App.module.css
index 2dfe36b..02d0625 100644
--- a/src/app/App.module.css
+++ b/src/app/App.module.css
@@ -13,6 +13,9 @@
   border-bottom: var(--border-width) solid var(--border);
   background: var(--layer-01);
   flex: 0 0 auto;
+  /* The header sits on --layer-01, so ghost/secondary controls step their hover
+     fill up to --layer-02 (arch 09 §4; consumed by Button/IconButton). */
+  --control-hover-fill: var(--layer-02);
 }
 
 .title {
@@ -61,42 +64,9 @@
   flex: 1;
 }
 
-/*
- * Header utility buttons (Datasets / Import / Export / About) — low-emphasis
- * ghost buttons: borderless, icon + label, so they recede behind the work area
- * and read as a row of equals (Carbon: utilities in toolbars/dashboards belong at
- * low emphasis). The transparent border holds the box size so hover doesn't shift
- * neighbours. Matches the ThemeToggle's ghost icon button beside them.
- */
-.headerButton {
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-2);
-  height: 32px;
-  padding: 0 var(--space-3);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-size: 13px;
-  font-weight: 500;
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.headerButton:hover {
-  background: var(--layer-02);
-}
-
-.headerButton:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-/* Vertical rule separating the utilities from Donate + the theme toggle. */
+/* Vertical rule separating the utilities from Donate + the theme toggle.
+   (The header buttons themselves are the shared Button primitive — ghost
+   utilities, soft-accent Donate; arch 09 §4.) */
 .headerDivider {
   flex: 0 0 auto;
   width: var(--border-width);
@@ -105,22 +75,6 @@
   background: var(--border-strong);
 }
 
-/*
- * Donate — the one solicitation in the header. A soft-accent wash lifts it just
- * above the ghost utilities without competing with a primary action (it carries
- * no border; the tint alone distinguishes it). Placed after .headerButton:hover
- * so its own hover state wins the equal-specificity tie.
- */
-.donate {
-  background: var(--accent-soft);
-  color: var(--accent-hover);
-}
-
-.donate:hover {
-  background: var(--accent-soft-hover);
-  color: var(--accent-hover);
-}
-
 /* The Import file picker is driven programmatically by its header button. */
 .hiddenInput {
   display: none;
diff --git a/src/app/App.tsx b/src/app/App.tsx
index 9f0a658..888618e 100644
--- a/src/app/App.tsx
+++ b/src/app/App.tsx
@@ -1,4 +1,5 @@
 import { useEffect, useRef } from 'react';
+import { Button } from './components/Button';
 import { ConfirmDialog } from './components/ConfirmDialog';
 import { LivePreview } from './components/LivePreview';
 import { ModalShell } from './components/ModalShell';
@@ -80,52 +81,46 @@ export function App() {
             better at low emphasis). The utilities are ghost (borderless) buttons
             with a leading icon for scanning; a divider then sets off Donate — the
             one solicitation, given a soft-accent wash — and the theme toggle. */}
-        <button
-          type="button"
-          className={styles.headerButton}
+        <Button
+          variant="ghost"
           onClick={() => openModal('datasets')}
           aria-keyshortcuts="Meta+K Control+K"
           title="Datasets (⌘/Ctrl+K)"
         >
           <Icon name="dataset" />
           Datasets
-        </button>
-        <button
-          type="button"
-          className={styles.headerButton}
+        </Button>
+        <Button
+          variant="ghost"
           onClick={() => fileInputRef.current?.click()}
           title="Import a workspace JSON file"
         >
           <Icon name="import" />
           Import
-        </button>
-        <button
-          type="button"
-          className={styles.headerButton}
+        </Button>
+        {/* TODO: two controls labelled "Export" are visible at once (this
+            workspace export + the preview pane's per-chart export) — rename or
+            differentiate (docs/ux-second-pass.md). */}
+        <Button
+          variant="ghost"
           onClick={() => exportWorkspace()}
           title="Export your workspace to a JSON file"
         >
           <Icon name="export" />
           Export
-        </button>
-        <button
-          type="button"
-          className={styles.headerButton}
+        </Button>
+        <Button
+          variant="ghost"
           onClick={() => openModal('about')}
           title="About, keyboard shortcuts, and privacy information"
         >
           <Icon name="info" />
           About
-        </button>
+        </Button>
         <span className={styles.headerDivider} aria-hidden="true" />
-        <button
-          type="button"
-          className={`${styles.headerButton} ${styles.donate}`}
-          onClick={() => openModal('donate')}
-          title="Support Astrolabe"
-        >
+        <Button variant="soft-accent" onClick={() => openModal('donate')} title="Support Astrolabe">
           Donate
-        </button>
+        </Button>
         <ThemeToggle />
         {/* Hidden picker for Import; restricted to JSON (spec §08). */}
         <input
diff --git a/src/app/components/Button.module.css b/src/app/components/Button.module.css
new file mode 100644
index 0000000..1635dfd
--- /dev/null
+++ b/src/app/components/Button.module.css
@@ -0,0 +1,107 @@
+/*
+ * Button — shared look for every textual action button (arch 09 §4). Owned here,
+ * once. Heights come from the control scale in tokens.css; no other button
+ * heights exist in the app.
+ */
+
+.button {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--space-2);
+  height: var(--control-height);
+  padding: 0 var(--space-3);
+  border: var(--border-width) solid transparent;
+  border-radius: var(--radius);
+  background: transparent;
+  color: var(--text);
+  font: inherit;
+  font-size: 13px;
+  font-weight: 600;
+  line-height: 1;
+  white-space: nowrap;
+  cursor: pointer;
+  transition:
+    background var(--dur-fast) var(--ease),
+    color var(--dur-fast) var(--ease);
+}
+
+.lg {
+  height: var(--control-height-lg);
+  padding: 0 var(--space-4);
+}
+
+.button:disabled {
+  cursor: default;
+  opacity: 0.45;
+}
+
+/* --- primary: filled accent; darkens on hover (filled buttons darken, they
+       don't fill — arch 09 §4) --- */
+.primary {
+  background: var(--accent);
+  color: var(--accent-contrast);
+}
+
+.primary:hover:not(:disabled) {
+  background: var(--accent-hover);
+}
+
+/* --- secondary: bordered with a --bg fill — the same field-on-layer treatment
+       as inputs/selects (arch 09 §4: a bordered control on a gray panel goes
+       white, never a darker gray); hover steps one elevation above the surface
+       (see --control-hover-fill in Button.tsx header) --- */
+.secondary {
+  border-color: var(--border-strong);
+  background: var(--bg);
+}
+
+.secondary:hover:not(:disabled) {
+  background: var(--control-hover-fill, var(--layer-01));
+}
+
+/* --- ghost: borderless utility; recedes until hover --- */
+.ghost:hover:not(:disabled) {
+  background: var(--control-hover-fill, var(--layer-01));
+}
+
+/* A ghost acting as an open disclosure trigger holds the pressed fill. */
+.ghost[aria-expanded='true'] {
+  background: var(--layer-02);
+}
+
+/* --- soft-accent: tinted-but-quiet solicitation (e.g. Donate) --- */
+.softAccent {
+  background: var(--accent-soft);
+  color: var(--accent-hover);
+}
+
+.softAccent:hover:not(:disabled) {
+  background: var(--accent-soft-hover);
+  color: var(--accent-hover);
+}
+
+/* --- danger: filled error for destructive confirm actions --- */
+.danger {
+  background: var(--support-error);
+  color: var(--on-status);
+}
+
+.danger:hover:not(:disabled) {
+  filter: brightness(0.92);
+}
+
+/* --- danger-outline: secondary geometry, red label; fills solid red on
+       hover/focus so the destructive intent is signalled before it acts --- */
+.dangerOutline {
+  border-color: var(--border-strong);
+  background: var(--bg);
+  color: var(--support-error);
+}
+
+.dangerOutline:hover:not(:disabled),
+.dangerOutline:focus-visible {
+  background: var(--support-error);
+  border-color: transparent;
+  color: var(--on-status);
+}
diff --git a/src/app/components/Button.test.tsx b/src/app/components/Button.test.tsx
new file mode 100644
index 0000000..9099934
--- /dev/null
+++ b/src/app/components/Button.test.tsx
@@ -0,0 +1,79 @@
+import { afterEach, beforeEach, describe, expect, test } from 'vitest';
+import { act } from 'react';
+import { createRoot, type Root } from 'react-dom/client';
+import { Button } from './Button';
+import { IconButton } from './IconButton';
+
+(globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
+
+let container: HTMLDivElement;
+let root: Root;
+
+beforeEach(() => {
+  container = document.createElement('div');
+  document.body.appendChild(container);
+  root = createRoot(container);
+});
+
+afterEach(() => {
+  act(() => root.unmount());
+  container.remove();
+});
+
+function render(node: React.ReactNode) {
+  act(() => root.render(node));
+  const button = container.querySelector('button');
+  if (!button) throw new Error('no <button> rendered');
+  return button;
+}
+
+describe('Button', () => {
+  test('defaults to type="button" so it never submits an enclosing form', () => {
+    expect(render(<Button>Save</Button>).getAttribute('type')).toBe('button');
+    expect(render(<Button type="submit">Save</Button>).getAttribute('type')).toBe('submit');
+  });
+
+  test('each variant resolves to a distinct class string', () => {
+    // Whatever the CSS-module hashing, the variants must produce different
+    // classes so the arch 09 §4 taxonomy is actually applied, not ignored.
+    const classes = (
+      ['primary', 'secondary', 'ghost', 'soft-accent', 'danger', 'danger-outline'] as const
+    ).map((variant) => render(<Button variant={variant}>X</Button>).className);
+    expect(new Set(classes).size).toBe(classes.length);
+  });
+
+  test('size and call-site classes compose onto the base class', () => {
+    // Capture the string before the next render — re-rendering reuses the node.
+    const mdClass = render(<Button>X</Button>).className;
+    const lg = render(
+      <Button size="lg" className="layout">
+        X
+      </Button>,
+    );
+    expect(lg.className).not.toBe(mdClass);
+    expect(lg.classList.contains('layout')).toBe(true);
+  });
+});
+
+describe('IconButton', () => {
+  test('label provides the accessible name and the default tooltip', () => {
+    const btn = render(<IconButton label="Close" />);
+    expect(btn.getAttribute('aria-label')).toBe('Close');
+    expect(btn.getAttribute('title')).toBe('Close');
+  });
+
+  test('an explicit title overrides the tooltip but not the accessible name', () => {
+    const btn = render(<IconButton label="Datasets" title="Datasets (⌘/Ctrl+K)" />);
+    expect(btn.getAttribute('aria-label')).toBe('Datasets');
+    expect(btn.getAttribute('title')).toBe('Datasets (⌘/Ctrl+K)');
+  });
+
+  test('defaults to type="button" and composes size/call-site classes', () => {
+    const md = render(<IconButton label="X" />);
+    expect(md.getAttribute('type')).toBe('button');
+    const mdClass = md.className;
+    const sm = render(<IconButton label="X" size="sm" className="reveal" />);
+    expect(sm.className).not.toBe(mdClass);
+    expect(sm.classList.contains('reveal')).toBe(true);
+  });
+});
diff --git a/src/app/components/Button.tsx b/src/app/components/Button.tsx
new file mode 100644
index 0000000..e290c3e
--- /dev/null
+++ b/src/app/components/Button.tsx
@@ -0,0 +1,74 @@
+/**
+ * Button — the shared action-button primitive (arch 09 §4).
+ *
+ * Every textual action button in the app is one of these. The component owns the
+ * base look (Button.module.css) so instances can't drift; call sites compose
+ * `className` for layout-specific additions only (flex, margins), never to
+ * restyle the control.
+ *
+ * Variants are the arch 09 §4 taxonomy:
+ * - **primary** — filled `--accent`; at most one per region (emphasis hierarchy).
+ * - **secondary** — bordered, `--bg` fill (the field-on-layer treatment).
+ * - **ghost** — borderless; utilities in toolbars/headers that should recede.
+ *   (A transparent border still holds the box size so hover doesn't shift
+ *   neighbours.)
+ * - **soft-accent** — ghost on an `--accent-soft` wash; low-emphasis solicitation.
+ * - **danger** — filled `--support-error`; destructive confirm actions.
+ * - **danger-outline** — secondary geometry with a red label, filling solid red
+ *   on hover/focus (arch 10 — a destructive control signals danger before it
+ *   acts). For destructive actions that sit among peers (a detail view's
+ *   Delete); the filled `danger` stays reserved for the confirm step.
+ *
+ * Sizes are the control scale (tokens.css): `md` = `--control-height` (32px, the
+ * default — toolbars, forms, dialog action rows), `lg` = `--control-height-lg`
+ * (40px — standalone primary CTAs).
+ *
+ * Hover on secondary/ghost fills one elevation step above the surface (arch 09
+ * §4). The step is resolved by the `--control-hover-fill` custom property:
+ * defaults to `--layer-01` (controls on the `--bg` canvas); elevated surfaces
+ * (the header, modal cards) set `--control-hover-fill: var(--layer-02)` once and
+ * every Button/IconButton on them steps up automatically.
+ */
+
+import type { ComponentPropsWithRef } from 'react';
+import styles from './Button.module.css';
+
+type ButtonVariant =
+  | 'primary'
+  | 'secondary'
+  | 'ghost'
+  | 'soft-accent'
+  | 'danger'
+  | 'danger-outline';
+
+export interface ButtonProps extends ComponentPropsWithRef<'button'> {
+  variant?: ButtonVariant;
+  size?: 'md' | 'lg';
+}
+
+const VARIANT_CLASS: Record<ButtonVariant, string> = {
+  primary: styles.primary,
+  secondary: styles.secondary,
+  ghost: styles.ghost,
+  'soft-accent': styles.softAccent,
+  danger: styles.danger,
+  'danger-outline': styles.dangerOutline,
+};
+
+export function Button({
+  variant = 'secondary',
+  size = 'md',
+  className,
+  type = 'button',
+  ...rest
+}: ButtonProps) {
+  return (
+    <button
+      type={type}
+      className={[styles.button, VARIANT_CLASS[variant], size === 'lg' && styles.lg, className]
+        .filter(Boolean)
+        .join(' ')}
+      {...rest}
+    />
+  );
+}
diff --git a/src/app/components/ChartExport.module.css b/src/app/components/ChartExport.module.css
index 114b761..9d94b4f 100644
--- a/src/app/components/ChartExport.module.css
+++ b/src/app/components/ChartExport.module.css
@@ -5,48 +5,7 @@
   display: inline-flex;
 }
 
-/* Trigger — a compact ghost button (icon + label), matching the header utilities. */
-.trigger {
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-2);
-  height: 28px;
-  padding: 0 var(--space-3);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text-secondary);
-  font: inherit;
-  font-size: 13px;
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.trigger:hover:not(:disabled) {
-  background: var(--layer-01);
-  color: var(--text);
-}
-
-.trigger[aria-expanded='true'] {
-  background: var(--layer-02);
-  color: var(--text);
-}
-
-.trigger:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 1px;
-}
-
-.trigger:disabled {
-  opacity: 0.45;
-  cursor: not-allowed;
-}
-
-.triggerIcon {
-  color: currentColor;
-}
+/* The trigger is the shared Button primitive (ghost; arch 09 §4). */
 
 /* The disclosed panel — portaled to <body>, positioned `fixed` (top/right set
    inline) so it escapes the panes' overflow clipping. Mirrors SettingsPopover. */
diff --git a/src/app/components/ChartExport.tsx b/src/app/components/ChartExport.tsx
index a5b148b..0f12fad 100644
--- a/src/app/components/ChartExport.tsx
+++ b/src/app/components/ChartExport.tsx
@@ -39,6 +39,7 @@ import { usePopover } from '../hooks/usePopover';
 import { useDatasetStore } from '../stores/DatasetStore';
 import { notify } from '../stores/NotificationStore';
 import { selectActiveSnippet, selectShownText, useSnippetStore } from '../stores/SnippetStore';
+import { Button } from './Button';
 import { Icon } from './Icon';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
 import { SettingRow } from './SettingsPopover';
@@ -183,19 +184,18 @@ export function ChartExport({ chartReady, getImageUrl }: ChartExportProps) {
 
   return (
     <div className={styles.wrap}>
-      <button
+      <Button
         ref={triggerRef}
-        type="button"
-        className={styles.trigger}
+        variant="ghost"
         aria-expanded={open}
         aria-controls={POP_ID}
         disabled={!hasSpec}
         title={hasSpec ? 'Export this chart' : 'Select a snippet to export'}
         onClick={toggle}
       >
-        <Icon name="export" className={styles.triggerIcon} />
+        <Icon name="export" />
         <span>Export</span>
-      </button>
+      </Button>
       {open &&
         createPortal(
           <div
diff --git a/src/app/components/ConfirmDialog.module.css b/src/app/components/ConfirmDialog.module.css
index 89f0279..2ca6e8d 100644
--- a/src/app/components/ConfirmDialog.module.css
+++ b/src/app/components/ConfirmDialog.module.css
@@ -21,6 +21,9 @@
   border-radius: var(--radius);
   /* Minimal shadow, reserved for true overlays (doc §09). */
   box-shadow: 0 2px 12px rgb(0 0 0 / 0.3);
+  /* The card sits on --layer-01, so its controls' hover fill steps up (the
+     collision that once left Cancel looking dead — arch 09 §4). */
+  --control-hover-fill: var(--layer-02);
 }
 
 .title {
@@ -44,49 +47,10 @@
   margin-top: var(--space-2);
 }
 
-.cancel,
-.confirm {
-  height: 40px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  font: inherit;
-  font-weight: 600;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
+/* The actions are shared Buttons (secondary / primary|danger, lg). These two
+   classes are pure markers — the focus trap's initial-focus selectors. */
 .cancel {
-  background: transparent;
-  border-color: var(--border-strong);
-  color: var(--text);
-}
-
-.cancel:hover {
-  background: var(--layer-02);
 }
 
 .confirm {
-  background: var(--accent);
-  color: var(--accent-contrast);
-}
-
-.confirm:hover {
-  background: var(--accent-hover);
-}
-
-.danger {
-  background: var(--support-error);
-  color: var(--on-status);
-}
-
-.danger:hover {
-  /* Slightly darken; the error token already carries the meaning. */
-  filter: brightness(0.92);
-}
-
-.cancel:focus-visible,
-.confirm:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
 }
diff --git a/src/app/components/ConfirmDialog.tsx b/src/app/components/ConfirmDialog.tsx
index b09b3fe..b9ec295 100644
--- a/src/app/components/ConfirmDialog.tsx
+++ b/src/app/components/ConfirmDialog.tsx
@@ -1,5 +1,6 @@
 import { useConfirmStore } from '../stores/ConfirmStore';
 import { useFocusTrap } from '../hooks/useFocusTrap';
+import { Button } from './Button';
 import styles from './ConfirmDialog.module.css';
 
 /**
@@ -42,16 +43,17 @@ export function ConfirmDialog() {
           {message}
         </p>
         <div className={styles.actions}>
-          <button type="button" className={styles.cancel} onClick={() => resolve(false)}>
+          <Button size="lg" className={styles.cancel} onClick={() => resolve(false)}>
             {cancelLabel ?? 'Cancel'}
-          </button>
-          <button
-            type="button"
-            className={`${styles.confirm} ${danger ? styles.danger : ''}`}
+          </Button>
+          <Button
+            size="lg"
+            variant={danger ? 'danger' : 'primary'}
+            className={styles.confirm}
             onClick={() => resolve(true)}
           >
             {confirmLabel ?? 'Confirm'}
-          </button>
+          </Button>
         </div>
       </div>
     </div>
diff --git a/src/app/components/DatasetsModal.module.css b/src/app/components/DatasetsModal.module.css
index d4c3892..86e4b4f 100644
--- a/src/app/components/DatasetsModal.module.css
+++ b/src/app/components/DatasetsModal.module.css
@@ -15,27 +15,10 @@
   border-right: var(--border-width) solid var(--border);
 }
 
+/* A shared primary Button (lg); locally just pinned with a margin. */
 .newButton {
   flex: 0 0 auto;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  gap: var(--space-2);
   margin: var(--space-4);
-  height: 40px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: var(--accent);
-  color: var(--accent-contrast);
-  font: inherit;
-  font-weight: 600;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.newButton:hover {
-  background: var(--accent-hover);
 }
 
 .list {
@@ -177,56 +160,7 @@
   justify-content: flex-end;
 }
 
-.action {
-  height: 32px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-size: 13px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.action:hover:not(:disabled) {
-  background: var(--layer-01);
-}
-
-.action:disabled {
-  color: var(--text-placeholder);
-  border-color: var(--border);
-  cursor: not-allowed;
-}
-
-.action:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-.primary {
-  background: var(--accent);
-  border-color: transparent;
-  color: var(--accent-contrast);
-  font-weight: 600;
-}
-
-.primary:hover:not(:disabled) {
-  background: var(--accent-hover);
-}
-
-.danger {
-  border-color: var(--border-strong);
-  color: var(--support-error);
-}
-
-.danger:hover:not(:disabled) {
-  background: var(--support-error);
-  color: var(--on-status);
-  border-color: transparent;
-}
+/* Actions are shared Buttons (secondary / primary / danger-outline). */
 
 .comment {
   margin: 0;
diff --git a/src/app/components/DatasetsModal.tsx b/src/app/components/DatasetsModal.tsx
index ee4dc08..eb3c507 100644
--- a/src/app/components/DatasetsModal.tsx
+++ b/src/app/components/DatasetsModal.tsx
@@ -37,6 +37,7 @@ import {
 } from '../stores/DatasetStore';
 import { useSnippetStore } from '../stores/SnippetStore';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
+import { Button } from './Button';
 import { Icon } from './Icon';
 import styles from './DatasetsModal.module.css';
 
@@ -73,9 +74,9 @@ export function DatasetsModal() {
   return (
     <div className={styles.manager}>
       <div className={styles.listPane}>
-        <button type="button" className={styles.newButton} onClick={handleNew}>
+        <Button variant="primary" size="lg" className={styles.newButton} onClick={handleNew}>
           <Icon name="add" /> New Dataset
-        </button>
+        </Button>
         <ul className={styles.list}>
           {ordered.length === 0 && (
             <li className={styles.empty}>
@@ -239,9 +240,7 @@ function DatasetDetail({
       <div className={styles.detailHead}>
         <h3 className={styles.detailName}>{dataset.name}</h3>
         <div className={styles.detailActions}>
-          <button type="button" className={styles.action} onClick={() => void handleCopy()}>
-            {copied ? 'Copied' : 'Copy Reference'}
-          </button>
+          <Button onClick={() => void handleCopy()}>{copied ? 'Copied' : 'Copy Reference'}</Button>
           {/* The clipboard write is invisible, so the success is confirmed inline
               ("Copied") rather than by a toast (docs/architecture/10 → Toast copy).
               This polite live region announces it to assistive tech, which the
@@ -250,35 +249,18 @@ function DatasetDetail({
             {copied ? 'Reference copied to clipboard' : ''}
           </span>
           {dataset.source === 'url' && (
-            <button
-              type="button"
-              className={styles.action}
-              onClick={() => void handleRefresh()}
-              disabled={refreshing}
-            >
+            <Button onClick={() => void handleRefresh()} disabled={refreshing}>
               {refreshing ? 'Refreshing…' : 'Refresh'}
-            </button>
+            </Button>
           )}
-          <button type="button" className={styles.action} onClick={handleEdit}>
-            Edit
-          </button>
+          <Button onClick={handleEdit}>Edit</Button>
           {/* Build Chart (spec §05 → §06) — opens the Chart Builder on this dataset.
               Replaces the Datasets modal (one modal at a time, §01C); detail view has
               no transient form state, so no discard prompt. */}
-          <button
-            type="button"
-            className={styles.action}
-            onClick={() => openModal('chartBuilder', String(dataset.id))}
-          >
-            Build Chart
-          </button>
-          <button
-            type="button"
-            className={`${styles.action} ${styles.danger}`}
-            onClick={() => void handleDelete()}
-          >
+          <Button onClick={() => openModal('chartBuilder', String(dataset.id))}>Build Chart</Button>
+          <Button variant="danger-outline" onClick={() => void handleDelete()}>
             Delete
-          </button>
+          </Button>
         </div>
       </div>
 
@@ -574,27 +556,18 @@ function DatasetFormView({ editing }: { editing: boolean }) {
       {/* A failed fetch is recoverable by pasting the data inline (the user's choice
           when CORS or offline blocks the URL) — offered as a direct one-click path. */}
       {fetchError && (
-        <button
-          type="button"
-          className={`${styles.action} ${styles.fallback}`}
-          onClick={handlePasteInline}
-        >
+        <Button className={styles.fallback} onClick={handlePasteInline}>
           Paste data inline instead
-        </button>
+        </Button>
       )}
 
       <div className={styles.formActions}>
-        <button type="button" className={styles.action} onClick={handleCancel} disabled={fetching}>
+        <Button onClick={handleCancel} disabled={fetching}>
           Cancel
-        </button>
-        <button
-          type="button"
-          className={`${styles.action} ${styles.primary}`}
-          disabled={!canSave || fetching}
-          onClick={() => void handleSave()}
-        >
+        </Button>
+        <Button variant="primary" disabled={!canSave || fetching} onClick={() => void handleSave()}>
           {fetching ? 'Fetching…' : editing ? 'Save changes' : 'Create dataset'}
-        </button>
+        </Button>
       </div>
     </div>
   );
diff --git a/src/app/components/DonateModal.module.css b/src/app/components/DonateModal.module.css
index cfb5975..d92cb78 100644
--- a/src/app/components/DonateModal.module.css
+++ b/src/app/components/DonateModal.module.css
@@ -26,7 +26,7 @@
   display: inline-flex;
   align-items: center;
   justify-content: center;
-  height: 36px;
+  height: var(--control-height-lg);
   padding: 0 var(--space-6);
   background: var(--accent);
   border: var(--border-width) solid transparent;
diff --git a/src/app/components/ExtractModal.module.css b/src/app/components/ExtractModal.module.css
index 94592eb..1164fae 100644
--- a/src/app/components/ExtractModal.module.css
+++ b/src/app/components/ExtractModal.module.css
@@ -74,41 +74,9 @@
   color: var(--support-error);
 }
 
+/* Cancel / Create are shared Buttons (secondary / primary, lg — modal footer). */
 .actions {
   display: flex;
   justify-content: flex-end;
   gap: var(--space-3);
 }
-
-.action {
-  height: 36px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-weight: 500;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.action:hover {
-  background: var(--layer-01);
-}
-
-.action:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-.primary {
-  background: var(--accent);
-  border-color: transparent;
-  color: var(--accent-contrast);
-  font-weight: 600;
-}
-
-.primary:hover {
-  background: var(--accent-hover);
-}
diff --git a/src/app/components/ExtractModal.tsx b/src/app/components/ExtractModal.tsx
index d876194..965ced7 100644
--- a/src/app/components/ExtractModal.tsx
+++ b/src/app/components/ExtractModal.tsx
@@ -11,6 +11,7 @@
 import { useShallow } from 'zustand/react/shallow';
 import { closeModal } from '../modals/ModalCoordinator';
 import { useExtractStore } from '../stores/ExtractStore';
+import { Button } from './Button';
 import styles from './ExtractModal.module.css';
 
 const MAX_PREVIEW = 1500;
@@ -74,16 +75,12 @@ export function ExtractModal() {
       )}
 
       <div className={styles.actions}>
-        <button type="button" className={styles.action} onClick={() => void closeModal()}>
+        <Button size="lg" onClick={() => void closeModal()}>
           Cancel
-        </button>
-        <button
-          type="button"
-          className={`${styles.action} ${styles.primary}`}
-          onClick={handleCreate}
-        >
+        </Button>
+        <Button variant="primary" size="lg" onClick={handleCreate}>
           Create dataset
-        </button>
+        </Button>
       </div>
     </div>
   );
diff --git a/src/app/components/IconButton.module.css b/src/app/components/IconButton.module.css
new file mode 100644
index 0000000..7a0b588
--- /dev/null
+++ b/src/app/components/IconButton.module.css
@@ -0,0 +1,48 @@
+/*
+ * IconButton — shared look for every icon-only button (arch 09 §4 + §5).
+ * Square, sized by the control scale in tokens.css.
+ */
+
+.iconButton {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  flex: 0 0 auto;
+  width: var(--control-height);
+  height: var(--control-height);
+  padding: 0;
+  border: var(--border-width) solid transparent;
+  border-radius: var(--radius);
+  background: transparent;
+  color: var(--text-secondary);
+  cursor: pointer;
+  transition:
+    background var(--dur-fast) var(--ease),
+    color var(--dur-fast) var(--ease);
+}
+
+.sm {
+  width: 24px;
+  height: 24px;
+}
+
+.lg {
+  width: var(--control-height-lg);
+  height: var(--control-height-lg);
+}
+
+.iconButton:hover:not(:disabled) {
+  background: var(--control-hover-fill, var(--layer-01));
+  color: var(--text);
+}
+
+/* An open disclosure trigger (gear popovers, export menu) holds the fill. */
+.iconButton[aria-expanded='true'] {
+  background: var(--layer-02);
+  color: var(--text);
+}
+
+.iconButton:disabled {
+  cursor: default;
+  opacity: 0.45;
+}
diff --git a/src/app/components/IconButton.tsx b/src/app/components/IconButton.tsx
new file mode 100644
index 0000000..6db063b
--- /dev/null
+++ b/src/app/components/IconButton.tsx
@@ -0,0 +1,53 @@
+/**
+ * IconButton — the shared icon-only button primitive (arch 09 §4 + §5).
+ *
+ * A square button holding a single `<Icon>` (the controlled-vocabulary glyph
+ * primitive) and nothing else. Because there is no visible text, an accessible
+ * name is required: `label` becomes `aria-label` (APG button pattern) and, unless
+ * overridden via `title`, the hover tooltip.
+ *
+ * Always ghost — borderless toolbar utility; the transparent border holds the
+ * box size. Sizes are the control scale: `md` = `--control-height` (32px
+ * square, the default), `lg` = `--control-height-lg` (40px — beside a lg
+ * Button), `sm` = 24px (only nested inside another 32px control, e.g. a search
+ * field's clear button).
+ *
+ * Hover follows the same one-elevation-step rule as Button, via the same
+ * `--control-hover-fill` custom property; an open disclosure trigger
+ * (`aria-expanded="true"`) holds the `--layer-02` fill.
+ */
+
+import type { ComponentPropsWithRef } from 'react';
+import styles from './IconButton.module.css';
+
+export interface IconButtonProps extends ComponentPropsWithRef<'button'> {
+  /** Accessible name (required — there is no visible text). */
+  label: string;
+  size?: 'sm' | 'md' | 'lg';
+}
+
+export function IconButton({
+  label,
+  size = 'md',
+  className,
+  type = 'button',
+  title,
+  ...rest
+}: IconButtonProps) {
+  return (
+    <button
+      type={type}
+      aria-label={label}
+      title={title ?? label}
+      className={[
+        styles.iconButton,
+        size === 'sm' && styles.sm,
+        size === 'lg' && styles.lg,
+        className,
+      ]
+        .filter(Boolean)
+        .join(' ')}
+      {...rest}
+    />
+  );
+}
diff --git a/src/app/components/ModalShell.module.css b/src/app/components/ModalShell.module.css
index d20cde1..dd31d31 100644
--- a/src/app/components/ModalShell.module.css
+++ b/src/app/components/ModalShell.module.css
@@ -20,6 +20,9 @@
   border: var(--border-width) solid var(--border);
   border-radius: var(--radius);
   box-shadow: 0 2px 12px rgb(0 0 0 / 0.3);
+  /* Modal chrome sits on --layer-01, so ghost/secondary controls in the header
+     step their hover fill up (arch 09 §4). The body resets to --bg below. */
+  --control-hover-fill: var(--layer-02);
 }
 
 /* Large: the two-pane managers (Datasets). Definite height so inner panes scroll. */
@@ -66,32 +69,7 @@
   outline: none;
 }
 
-.close {
-  flex: 0 0 auto;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  width: 32px;
-  height: 32px;
-  border: none;
-  background: none;
-  color: var(--text-secondary);
-  font-size: 22px;
-  line-height: 1;
-  cursor: pointer;
-  border-radius: var(--radius);
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.close:hover {
-  background: var(--layer-02);
-  color: var(--text);
-}
-
-.close:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
+/* The close affordance is the shared IconButton. */
 
 /* The modal body. Background steps to --bg so the panes read as the work surface
    against the --layer-01 chrome. Fills the remaining height; inner content scrolls. */
@@ -100,4 +78,5 @@
   min-height: 0;
   overflow: auto;
   background: var(--bg);
+  --control-hover-fill: var(--layer-01);
 }
diff --git a/src/app/components/ModalShell.tsx b/src/app/components/ModalShell.tsx
index c0fe642..f221142 100644
--- a/src/app/components/ModalShell.tsx
+++ b/src/app/components/ModalShell.tsx
@@ -27,6 +27,7 @@ import { DonateModal } from './DonateModal';
 import { ExtractModal } from './ExtractModal';
 import { ThemeBuilderModal } from './ThemeBuilderModal';
 import { Icon } from './Icon';
+import { IconButton } from './IconButton';
 import styles from './ModalShell.module.css';
 
 /** The body rendered for each modal name (metadata stays in the registry). */
@@ -95,14 +96,9 @@ export function ModalShell() {
           <h2 id="modal-title" className={styles.title} tabIndex={-1}>
             {getModalTitle(name)}
           </h2>
-          <button
-            type="button"
-            className={styles.close}
-            aria-label="Close"
-            onClick={() => void closeModal()}
-          >
+          <IconButton label="Close" onClick={() => void closeModal()}>
             <Icon name="close" />
-          </button>
+          </IconButton>
         </header>
         <div className={styles.body}>
           <Body />
diff --git a/src/app/components/Onboarding.module.css b/src/app/components/Onboarding.module.css
index 9d1eb38..ab414ca 100644
--- a/src/app/components/Onboarding.module.css
+++ b/src/app/components/Onboarding.module.css
@@ -35,53 +35,7 @@
   gap: var(--space-3);
 }
 
-/* Primary call to action — the accent button, matching the library's Create. */
-.primary {
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-2);
-  height: 40px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: var(--accent);
-  color: var(--accent-contrast);
-  font: inherit;
-  font-weight: 600;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-.primary:hover {
-  background: var(--accent-hover);
-}
-.primary:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-/* The data-first door — bordered ghost, same height as the primary beside it. */
-.buildCta {
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-2);
-  height: 40px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-weight: 600;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-.buildCta:hover {
-  background: var(--layer-01);
-}
-.buildCta:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
+/* The two CTAs and the per-example Adds are shared Buttons (arch 09 §4). */
 
 /* The "or start from an example" header row, with Add all pushed to the end. */
 .galleryHead {
@@ -101,27 +55,8 @@
   color: var(--text-secondary);
 }
 
-/* Secondary button — bordered, transparent (like the header actions). */
 .addAll {
   flex: 0 0 auto;
-  height: 32px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-size: 13px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-.addAll:hover {
-  background: var(--layer-01);
-}
-.addAll:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
 }
 
 /* Responsive gallery: cards as wide as ~240px, filling the column. */
@@ -174,28 +109,7 @@
   line-height: 1.4;
 }
 
-/* Per-example Add — small bordered action, aligned to the card's start. */
+/* Per-example Add — a shared secondary Button, aligned to the card's start. */
 .add {
   align-self: flex-start;
-  display: inline-flex;
-  align-items: center;
-  gap: var(--space-1);
-  height: 30px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: var(--bg);
-  color: var(--text);
-  font: inherit;
-  font-size: 13px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-.add:hover {
-  background: var(--layer-02, var(--layer-01));
-}
-.add:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
 }
diff --git a/src/app/components/Onboarding.tsx b/src/app/components/Onboarding.tsx
index ba6b8e6..fae3033 100644
--- a/src/app/components/Onboarding.tsx
+++ b/src/app/components/Onboarding.tsx
@@ -24,6 +24,7 @@ import { renderSpec, type RenderHandle } from '../services/chart-renderer';
 import { useAppStore } from '../stores/AppStore';
 import { usePanesStore } from '../stores/PanesStore';
 import { useSnippetStore } from '../stores/SnippetStore';
+import { Button } from './Button';
 import { Icon } from './Icon';
 import styles from './Onboarding.module.css';
 
@@ -141,19 +142,19 @@ export function Onboarding() {
         </p>
 
         <div className={styles.ctaRow}>
-          <button type="button" className={styles.primary} onClick={handleCreate}>
+          <Button variant="primary" size="lg" onClick={handleCreate}>
             <Icon name="add" /> Create your first snippet
-          </button>
-          <button type="button" className={styles.buildCta} onClick={handleBuild}>
+          </Button>
+          <Button size="lg" onClick={handleBuild}>
             <Icon name="chart" /> Build a chart from your data
-          </button>
+          </Button>
         </div>
 
         <div className={styles.galleryHead}>
           <h3 className={styles.galleryTitle}>Or start from an example</h3>
-          <button type="button" className={styles.addAll} onClick={handleAddAll}>
+          <Button className={styles.addAll} onClick={handleAddAll}>
             Add all
-          </button>
+          </Button>
         </div>
 
         <ul className={styles.gallery}>
@@ -164,14 +165,13 @@ export function Onboarding() {
                 <span className={styles.cardName}>{example.name}</span>
                 <span className={styles.cardDesc}>{example.description}</span>
               </div>
-              <button
-                type="button"
+              <Button
                 className={styles.add}
                 aria-label={`Add ${example.name}`}
                 onClick={() => handleAdd(example)}
               >
                 <Icon name="add" /> Add
-              </button>
+              </Button>
             </li>
           ))}
         </ul>
diff --git a/src/app/components/PaneToggleStrip.module.css b/src/app/components/PaneToggleStrip.module.css
index c285777..5f61f62 100644
--- a/src/app/components/PaneToggleStrip.module.css
+++ b/src/app/components/PaneToggleStrip.module.css
@@ -12,41 +12,19 @@
   padding: var(--space-3) var(--space-2);
   border-right: var(--border-width) solid var(--border);
   background: var(--layer-01);
+  /* The strip sits on --layer-01, so the IconButtons' hover fill steps up. */
+  --control-hover-fill: var(--layer-02);
 }
 
-.button {
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  width: 32px;
-  height: 32px;
-  padding: 0;
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: transparent;
-  /* Not-pressed (hidden pane) reads as muted; pressed (shown) lifts to full text. */
-  color: var(--text-secondary);
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.button:hover {
-  background: var(--layer-02);
-  color: var(--text);
-}
-
-.button:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-/* Shown pane: the toggle is "on" — full-strength glyph on a filled chip. */
-.pressed {
+/* The controls are shared IconButtons; only the toggle-on state is local.
+   Shown pane: the toggle is "on" — full-strength glyph on a filled chip.
+   (.strip prefix outranks the primitive's base background/color.) */
+/* TODO: the pressed chip (--layer-02 fill) is identical to the IconButton hover
+   fill on this surface, so hovering an off toggle looks the same as an on toggle
+   at rest — the pressed state needs its own cue (docs/ux-second-pass.md). */
+.strip .pressed {
   color: var(--text);
   background: var(--layer-02);
-  border-color: var(--border-strong);
 }
 
 .divider {
diff --git a/src/app/components/PaneToggleStrip.tsx b/src/app/components/PaneToggleStrip.tsx
index 50df0f1..a7cdd8e 100644
--- a/src/app/components/PaneToggleStrip.tsx
+++ b/src/app/components/PaneToggleStrip.tsx
@@ -23,6 +23,7 @@ import { useRef, useState } from 'react';
 import { openModal } from '../modals/ModalCoordinator';
 import { usePanesStore, type PaneName } from '../stores/PanesStore';
 import { Icon, type IconName } from './Icon';
+import { IconButton } from './IconButton';
 import styles from './PaneToggleStrip.module.css';
 
 interface PaneItem {
@@ -105,14 +106,13 @@ export function PaneToggleStrip() {
       className={styles.strip}
     >
       {PANES.map((item, i) => (
-        <button
+        <IconButton
           key={item.pane}
           ref={(el) => {
             refs.current[i] = el;
           }}
-          type="button"
           aria-pressed={visible[item.pane]}
-          aria-label={item.label}
+          label={item.label}
           // Only point at the pane while it's actually mounted: App unmounts a
           // hidden pane's <section>, so emitting aria-controls then would leave a
           // dangling IDREF (invalid, even if AT ignores it). The association is
@@ -124,9 +124,7 @@ export function PaneToggleStrip() {
           // stable (aria-label) per APG's toggle-button rule.
           title={`${visible[item.pane] ? 'Hide' : 'Show'} ${item.label.toLowerCase()}`}
           tabIndex={focusIndex === i ? 0 : -1}
-          className={[styles.button, visible[item.pane] && styles.pressed]
-            .filter(Boolean)
-            .join(' ')}
+          className={visible[item.pane] ? styles.pressed : undefined}
           onClick={() => {
             togglePane(item.pane, panesInner());
             setFocusIndex(i);
@@ -134,21 +132,19 @@ export function PaneToggleStrip() {
           onKeyDown={(e) => onKeyDown(e, i)}
         >
           <Icon name={item.icon} />
-        </button>
+        </IconButton>
       ))}
 
       <div className={styles.divider} aria-hidden="true" />
 
-      <button
+      <IconButton
         ref={(el) => {
           refs.current[datasetsIndex] = el;
         }}
-        type="button"
-        aria-label="Datasets"
+        label="Datasets"
         aria-keyshortcuts="Meta+K Control+K"
         title="Datasets (⌘/Ctrl+K)"
         tabIndex={focusIndex === datasetsIndex ? 0 : -1}
-        className={styles.button}
         onClick={() => {
           openModal('datasets');
           setFocusIndex(datasetsIndex);
@@ -156,7 +152,7 @@ export function PaneToggleStrip() {
         onKeyDown={(e) => onKeyDown(e, datasetsIndex)}
       >
         <Icon name="dataset" />
-      </button>
+      </IconButton>
     </div>
   );
 }
diff --git a/src/app/components/SegmentedControl.module.css b/src/app/components/SegmentedControl.module.css
index ea0e5cd..a642c4e 100644
--- a/src/app/components/SegmentedControl.module.css
+++ b/src/app/components/SegmentedControl.module.css
@@ -8,18 +8,22 @@
  */
 .group {
   display: inline-flex;
+  /* The control scale (tokens.css): the 1px borders live inside the 32px box. */
+  height: var(--control-height);
   border: var(--border-width) solid var(--border-strong);
 }
 
 .option {
   appearance: none;
+  display: inline-flex;
+  align-items: center;
   border: none;
   background: var(--bg);
   color: var(--text-secondary);
   font: inherit;
-  font-size: 12px;
+  font-size: 13px;
   line-height: 1;
-  padding: var(--space-2) var(--space-3);
+  padding: 0 var(--space-3);
   cursor: pointer;
   transition:
     background var(--dur-fast) var(--ease),
diff --git a/src/app/components/SelectControl.module.css b/src/app/components/SelectControl.module.css
index f3d7a79..96f1e42 100644
--- a/src/app/components/SelectControl.module.css
+++ b/src/app/components/SelectControl.module.css
@@ -6,7 +6,7 @@
   display: inline-flex;
   align-items: center;
   gap: var(--space-2);
-  height: 32px;
+  height: var(--control-height);
   padding: 0 var(--space-3);
   border: var(--border-width) solid var(--border-strong);
   border-radius: var(--radius);
diff --git a/src/app/components/SettingsPopover.module.css b/src/app/components/SettingsPopover.module.css
index 205c66d..a3f838d 100644
--- a/src/app/components/SettingsPopover.module.css
+++ b/src/app/components/SettingsPopover.module.css
@@ -5,38 +5,7 @@
   display: inline-flex;
 }
 
-/* Gear trigger — a subtle icon button matching the modal-shell close affordance. */
-.gear {
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 28px;
-  height: 28px;
-  padding: 0;
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text-secondary);
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.gear:hover {
-  background: var(--layer-01);
-  color: var(--text);
-}
-
-.gear[aria-expanded='true'] {
-  background: var(--layer-02);
-  color: var(--text);
-}
-
-.gear:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 1px;
-}
+/* The gear trigger is the shared IconButton primitive (arch 09 §4). */
 
 /* The disclosed panel — portaled to <body>, positioned `fixed` from the gear's
    rect (top/left|right set inline) so it escapes the panes' overflow clipping. */
@@ -66,7 +35,8 @@
   align-items: center;
   justify-content: space-between;
   gap: var(--space-4);
-  min-height: 32px;
+  /* Rows hold 32px controls; the min keeps control-less rows the same height. */
+  min-height: var(--control-height);
 }
 
 .row + .row {
@@ -109,7 +79,8 @@
 
 .number,
 .text {
-  padding: var(--space-2) var(--space-3);
+  height: var(--control-height);
+  padding: 0 var(--space-3);
   border: var(--border-width) solid var(--border-strong);
   border-radius: var(--radius);
   background: var(--bg);
diff --git a/src/app/components/SettingsPopover.tsx b/src/app/components/SettingsPopover.tsx
index 4bd3122..8d45ff8 100644
--- a/src/app/components/SettingsPopover.tsx
+++ b/src/app/components/SettingsPopover.tsx
@@ -23,6 +23,7 @@ import { type ReactNode } from 'react';
 import { createPortal } from 'react-dom';
 import { usePopover } from '../hooks/usePopover';
 import { Icon } from './Icon';
+import { IconButton } from './IconButton';
 import styles from './SettingsPopover.module.css';
 
 /** Focus the first interactive control on open (any kind — these are forms). */
@@ -55,18 +56,15 @@ export function SettingsPopover({
 
   return (
     <div className={styles.wrap}>
-      <button
+      <IconButton
         ref={triggerRef}
-        type="button"
-        className={styles.gear}
+        label={label}
         aria-expanded={open}
         aria-controls={id}
-        aria-label={label}
-        title={label}
         onClick={toggle}
       >
         <Icon name="settings" />
-      </button>
+      </IconButton>
       {open &&
         createPortal(
           <div ref={setPopNode} id={id} className={styles.pop} role="group" aria-label={title}>
diff --git a/src/app/components/SnippetLibrary.module.css b/src/app/components/SnippetLibrary.module.css
index 7ef8908..18e3cea 100644
--- a/src/app/components/SnippetLibrary.module.css
+++ b/src/app/components/SnippetLibrary.module.css
@@ -37,55 +37,14 @@
   margin: var(--space-4);
 }
 
+/* Both creators are the shared Button primitive (primary / secondary, lg);
+   locally they only divide the row's width. */
 .createNew {
   flex: 1 1 auto;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  gap: var(--space-2);
-  height: 40px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: var(--accent);
-  color: var(--accent-contrast);
-  font: inherit;
-  font-weight: 600;
-  /* The label never wraps: above the collapse width the pane is wide enough for one
-     line; below it, only the icon shows. */
-  white-space: nowrap;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
 }
 
-.createNew:hover {
-  background: var(--accent-hover);
-}
-
-/* The expert accelerator: a quiet bordered ghost beside the primary. */
 .createGhost {
   flex: 0 1 auto;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  gap: var(--space-2);
-  height: 40px;
-  padding: 0 var(--space-3);
-  border: var(--border-width) solid var(--border);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text-secondary);
-  font: inherit;
-  white-space: nowrap;
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.createGhost:hover {
-  background: var(--layer-01);
-  color: var(--text);
 }
 
 /* Two-stage label collapse as the pane narrows: the long ghost label goes first
@@ -135,7 +94,7 @@
      intrinsic content width (~20ch), which otherwise overflowed the slot and slid
      over the Sort trigger at the pane minimum. */
   min-width: 0;
-  height: 32px;
+  height: var(--control-height);
   /* Room for the leading magnifier and the trailing clear button. */
   padding: 0 32px 0 32px;
   border: var(--border-width) solid var(--border-strong);
@@ -161,33 +120,11 @@
   appearance: none;
 }
 
+/* The clear affordance is a shared IconButton (sm — nested inside the 32px
+   field); locally it is only pinned to the input's trailing edge. */
 .searchClear {
   position: absolute;
   right: var(--space-2);
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 24px;
-  height: 24px;
-  padding: 0;
-  border: none;
-  border-radius: var(--radius);
-  background: none;
-  color: var(--text-secondary);
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.searchClear:hover {
-  background: var(--layer-01);
-  color: var(--text);
-}
-
-.searchClear:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 1px;
 }
 
 /* Visually-hidden live region for the search result count (council SEARCH). */
@@ -341,33 +278,27 @@
   color: var(--text-placeholder);
 }
 
+/* Row trash — a shared IconButton (sm); locally it only handles the row-hover
+   reveal and the destructive hover colour. */
 .delete {
-  flex: 0 0 auto;
   align-self: center;
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  border: none;
-  background: none;
-  color: var(--text-secondary);
-  cursor: pointer;
-  padding: var(--space-2);
-  border-radius: var(--radius);
   opacity: 0;
   transition:
     opacity var(--dur-fast) var(--ease),
+    background var(--dur-fast) var(--ease),
     color var(--dur-fast) var(--ease);
 }
 
 .item:hover .delete,
-.delete:focus-visible {
+.item .delete:focus-visible {
   opacity: 1;
 }
 
 /* Destructive intent reddens on hover AND keyboard focus, not colour-by-mouse-only
-   (arch 10 — destructive controls signal danger on hover/focus). */
-.delete:hover,
-.delete:focus-visible {
+   (arch 10 — destructive controls signal danger on hover/focus). The .item prefix
+   outranks the IconButton primitive's own hover colour. */
+.item .delete:hover,
+.item .delete:focus-visible {
   color: var(--support-error);
 }
 
@@ -385,6 +316,8 @@
   padding: var(--space-4);
   border-top: var(--border-width) solid var(--border);
   background: var(--layer-01);
+  /* The panel sits on --layer-01, so its controls' hover fill steps up. */
+  --control-hover-fill: var(--layer-02);
 }
 
 .metaField {
@@ -418,6 +351,8 @@
 }
 
 .metaName {
+  height: var(--control-height);
+  padding: 0 var(--space-3);
   font-weight: 500;
 }
 
@@ -495,30 +430,7 @@
   margin-top: var(--space-1);
 }
 
+/* Shared Buttons (secondary / danger-outline); locally they only split the row. */
 .metaAction {
   flex: 1 1 auto;
-  height: 32px;
-  padding: 0 var(--space-3);
-  /* White on the gray panel, same field-on-layer treatment as the inputs above. */
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: var(--bg);
-  color: var(--text);
-  font: inherit;
-  font-size: 12px;
-  font-weight: 500;
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    border-color var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.metaAction:hover {
-  background: var(--layer-02);
-}
-
-.metaDanger:hover {
-  color: var(--support-error);
-  border-color: var(--support-error);
 }
diff --git a/src/app/components/SnippetLibrary.tsx b/src/app/components/SnippetLibrary.tsx
index aae5bd1..ecb283a 100644
--- a/src/app/components/SnippetLibrary.tsx
+++ b/src/app/components/SnippetLibrary.tsx
@@ -25,7 +25,9 @@ import { confirm } from '../stores/ConfirmStore';
 import { notify } from '../stores/NotificationStore';
 import { selectActiveSnippet, useSnippetStore } from '../stores/SnippetStore';
 import { useUserSettingsStore } from '../stores/UserSettingsStore';
+import { Button } from './Button';
 import { Icon } from './Icon';
+import { IconButton } from './IconButton';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
 import { SettingRow, SettingsPopover, TextControl } from './SettingsPopover';
 import { SortControl } from './SortControl';
@@ -162,16 +164,12 @@ function SnippetMeta({
       )}
 
       <div className={styles.metaActions}>
-        <button type="button" className={styles.metaAction} onClick={onDuplicate}>
+        <Button className={styles.metaAction} onClick={onDuplicate}>
           Duplicate
-        </button>
-        <button
-          type="button"
-          className={`${styles.metaAction} ${styles.metaDanger}`}
-          onClick={onDelete}
-        >
+        </Button>
+        <Button variant="danger-outline" className={styles.metaAction} onClick={onDelete}>
           Delete
-        </button>
+        </Button>
       </div>
     </section>
   );
@@ -260,7 +258,9 @@ export function SnippetLibrary() {
           pane is dragged narrow the labels collapse to icons (a @container
           query); `aria-label` keeps each accessible name. */}
       <div className={styles.createRow}>
-        <button
+        <Button
+          variant="primary"
+          size="lg"
           className={styles.createNew}
           onClick={() => openModal('chartBuilder')}
           aria-label="Build Chart"
@@ -268,8 +268,9 @@ export function SnippetLibrary() {
         >
           <Icon name="chart" />
           <span className={styles.createNewLabel}>Build Chart</span>
-        </button>
-        <button
+        </Button>
+        <Button
+          size="lg"
           className={styles.createGhost}
           onClick={() => createSnippet()}
           aria-label="New JSON snippet"
@@ -277,7 +278,7 @@ export function SnippetLibrary() {
         >
           <Icon name="add" />
           <span className={styles.createNewLabel}>New JSON snippet</span>
-        </button>
+        </Button>
       </div>
 
       {/* Search + Sort controls, pinned above the list (spec §02; council
@@ -300,15 +301,14 @@ export function SnippetLibrary() {
             spellCheck={false}
           />
           {searching && (
-            <button
-              type="button"
+            <IconButton
+              size="sm"
               className={styles.searchClear}
-              aria-label="Clear search"
-              title="Clear search"
+              label="Clear search"
               onClick={clearSearch}
             >
               <Icon name="close" />
-            </button>
+            </IconButton>
           )}
         </div>
         <SortControl />
@@ -381,14 +381,15 @@ export function SnippetLibrary() {
                   )}
                 </span>
               </button>
-              <button
+              <IconButton
+                size="sm"
                 className={styles.delete}
-                aria-label={`Delete ${s.name}`}
+                label={`Delete ${s.name}`}
                 title="Delete snippet"
                 onClick={() => void handleDelete(s.id, s.name)}
               >
                 <Icon name="delete" />
-              </button>
+              </IconButton>
             </li>
           );
         })}
diff --git a/src/app/components/SortControl.module.css b/src/app/components/SortControl.module.css
index 1a49e25..2639163 100644
--- a/src/app/components/SortControl.module.css
+++ b/src/app/components/SortControl.module.css
@@ -10,13 +10,12 @@
 }
 
 /* Trigger — shows the current field + direction for recognition (council SORT).
-   32px tall to match the search input it sits beside (they shared a row at
-   mismatched 28/32px heights before). */
+   The standard control height, matching the search input it sits beside. */
 .trigger {
   display: inline-flex;
   align-items: center;
   gap: var(--space-1);
-  height: 32px;
+  height: var(--control-height);
   padding: 0 var(--space-3);
   border: var(--border-width) solid var(--border-strong);
   border-radius: var(--radius);
diff --git a/src/app/components/SpecEditor.module.css b/src/app/components/SpecEditor.module.css
index 08cb8cd..42f46ce 100644
--- a/src/app/components/SpecEditor.module.css
+++ b/src/app/components/SpecEditor.module.css
@@ -23,44 +23,12 @@
   flex: 1 1 auto;
 }
 
-/* Draft/Published toggle styling now lives in SegmentedControl.module.css. */
-
-/* Publish / Revert buttons. */
-.action {
-  appearance: none;
-  height: 28px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid var(--border-strong);
-  background: var(--bg);
-  color: var(--text);
-  font: inherit;
-  font-size: 12px;
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    border-color var(--dur-fast) var(--ease),
-    opacity var(--dur-fast) var(--ease);
-}
-
-.action:hover:not(:disabled) {
-  background: var(--layer-01);
-}
-
-.action:disabled {
-  opacity: 0.4;
-  cursor: default;
-}
+/* Toolbar controls are the shared primitives: Draft/Published is a
+   SegmentedControl, Publish/Revert/Extract are Buttons (arch 09 §4). */
 
 /* Collapsible secondary actions (Extract, Revert): label by default, icon-only
    when the pane is narrow. Both children live in the DOM always; the container
    query swaps which one shows, so there's no reflow cost beyond display. */
-.collapsible {
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  gap: var(--space-2);
-}
-
 .actionIcon {
   display: none;
 }
@@ -73,10 +41,11 @@
 /* Below this pane width the labels would crowd Publish / wrap, so the secondary
    actions shed their text and become square icon buttons (the accessible name +
    title keep them identifiable). 480px is comfortably above the 384px pane
-   minimum, so the collapse is in effect across the whole narrow range. */
+   minimum, so the collapse is in effect across the whole narrow range. The
+   .toolbar prefix outranks the Button primitive's own padding. */
 @container (max-width: 480px) {
-  .collapsible {
-    width: 28px;
+  .toolbar .collapsible {
+    width: var(--control-height);
     padding: 0;
   }
   .collapsible .actionLabel {
@@ -87,16 +56,6 @@
   }
 }
 
-.publish {
-  border-color: transparent;
-  background: var(--accent);
-  color: var(--accent-contrast);
-}
-
-.publish:hover:not(:disabled) {
-  background: var(--accent-hover);
-}
-
 .editorWrap {
   position: relative;
   flex: 1 1 auto;
diff --git a/src/app/components/SpecEditor.tsx b/src/app/components/SpecEditor.tsx
index b858567..6e68579 100644
--- a/src/app/components/SpecEditor.tsx
+++ b/src/app/components/SpecEditor.tsx
@@ -40,6 +40,7 @@ import { usePreviewStore } from '../stores/PreviewStore';
 import { selectActiveSnippet, selectShownText, useSnippetStore } from '../stores/SnippetStore';
 import { useUserSettingsStore } from '../stores/UserSettingsStore';
 import { Icon } from './Icon';
+import { Button } from './Button';
 import { SegmentedControl, type SegmentedOption } from './SegmentedControl';
 import { SelectControl } from './SelectControl';
 import {
@@ -239,16 +240,15 @@ function EditorToolbar({
           `title` (and the accessible name) when only the icon shows. Publish — the
           one primary action — keeps its label at every width. */}
       {canExtract && (
-        <button
-          type="button"
-          className={`${styles.action} ${styles.collapsible}`}
+        <Button
+          className={styles.collapsible}
           onClick={() => openModal('extract')}
           title="Extract inline data into a reusable dataset"
           aria-label="Extract to Dataset"
         >
           <Icon name="dataset" className={styles.actionIcon} />
           <span className={styles.actionLabel}>Extract to Dataset</span>
-        </button>
+        </Button>
       )}
       <SelectControl
         id="editor-config-actions"
@@ -256,14 +256,12 @@ function EditorToolbar({
         heading="Spec config"
         options={CONFIG_ACTIONS}
         onSelect={handleConfigAction}
-        triggerClassName={styles.action}
         triggerContent="Config"
         triggerTitle="Spec config actions — merge the chart theme in, or extract the config out"
         disabled={activeId === null || editorView === 'published'}
       />
-      <button
-        type="button"
-        className={`${styles.action} ${styles.collapsible}`}
+      <Button
+        className={styles.collapsible}
         onClick={() => void handleRevert()}
         disabled={activeId === null || !dirty}
         title="Revert draft to the last published version"
@@ -271,17 +269,16 @@ function EditorToolbar({
       >
         <Icon name="revert" className={styles.actionIcon} />
         <span className={styles.actionLabel}>Revert</span>
-      </button>
-      <button
-        type="button"
-        className={`${styles.action} ${styles.publish}`}
+      </Button>
+      <Button
+        variant="primary"
         onClick={handlePublish}
         disabled={activeId === null}
         title="Publish (⌘/Ctrl+S)"
         aria-keyshortcuts="Meta+S Control+S"
       >
         Publish
-      </button>
+      </Button>
       <EditorSettings />
     </div>
   );
diff --git a/src/app/components/ThemeBuilderModal.module.css b/src/app/components/ThemeBuilderModal.module.css
index ceb1937..343d887 100644
--- a/src/app/components/ThemeBuilderModal.module.css
+++ b/src/app/components/ThemeBuilderModal.module.css
@@ -18,27 +18,10 @@
   border-right: var(--border-width) solid var(--border);
 }
 
+/* A shared primary Button (lg); locally just pinned with a margin. */
 .newButton {
   flex: 0 0 auto;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  gap: var(--space-2);
   margin: var(--space-4);
-  height: 40px;
-  padding: 0 var(--space-5);
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: var(--accent);
-  color: var(--accent-contrast);
-  font: inherit;
-  font-weight: 600;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.newButton:hover {
-  background: var(--accent-hover);
 }
 
 .list {
@@ -136,7 +119,7 @@
 
 .input {
   width: 100%;
-  height: 32px;
+  height: var(--control-height);
   padding: 0 var(--space-3);
   border: var(--border-width) solid var(--border-strong);
   border-radius: var(--radius);
@@ -157,60 +140,7 @@
   gap: var(--space-3);
 }
 
-.action {
-  height: 32px;
-  padding: 0 var(--space-4);
-  border: var(--border-width) solid var(--border-strong);
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text);
-  font: inherit;
-  font-size: 13px;
-  font-weight: 500;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.action:hover:not(:disabled) {
-  background: var(--layer-01);
-}
-
-.action:disabled {
-  color: var(--text-placeholder);
-  border-color: var(--border);
-  cursor: not-allowed;
-}
-
-.action:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
-}
-
-.primary {
-  background: var(--accent);
-  border-color: transparent;
-  color: var(--accent-contrast);
-  font-weight: 600;
-}
-
-.primary:hover:not(:disabled) {
-  background: var(--accent-hover);
-}
-
-.primary:disabled {
-  background: var(--layer-01);
-}
-
-.danger {
-  border-color: var(--border-strong);
-  color: var(--support-error);
-}
-
-.danger:hover:not(:disabled) {
-  background: var(--support-error);
-  color: var(--on-status);
-  border-color: transparent;
-}
+/* Actions are shared Buttons (danger-outline / primary). */
 
 .errorMessage {
   flex: 0 0 auto;
diff --git a/src/app/components/ThemeBuilderModal.tsx b/src/app/components/ThemeBuilderModal.tsx
index 33300bf..95d72b8 100644
--- a/src/app/components/ThemeBuilderModal.tsx
+++ b/src/app/components/ThemeBuilderModal.tsx
@@ -26,6 +26,7 @@ import {
 } from '../stores/CustomThemeStore';
 import { notify } from '../stores/NotificationStore';
 import { resnapshot } from '../modals/ModalCoordinator';
+import { Button } from './Button';
 import { SelectControl } from './SelectControl';
 import styles from './ThemeBuilderModal.module.css';
 
@@ -152,9 +153,9 @@ export function ThemeBuilderModal() {
   return (
     <div className={styles.builder}>
       <div className={styles.listPane}>
-        <button type="button" className={styles.newButton} onClick={handleNew}>
+        <Button variant="primary" size="lg" className={styles.newButton} onClick={handleNew}>
           New theme
-        </button>
+        </Button>
         <ul className={styles.list}>
           {themes.length === 0 && (
             <li className={styles.empty}>
@@ -208,21 +209,16 @@ export function ThemeBuilderModal() {
               triggerTitle="Write one font family into every font slot of the config"
             />
             <div className={styles.toolbarEnd}>
-              <button
-                type="button"
-                className={`${styles.action} ${styles.danger}`}
-                onClick={() => void handleDelete()}
-              >
+              <Button variant="danger-outline" onClick={() => void handleDelete()}>
                 Delete
-              </button>
-              <button
-                type="button"
-                className={`${styles.action} ${styles.primary}`}
+              </Button>
+              <Button
+                variant="primary"
                 disabled={!dirty || parseError !== null}
                 onClick={handleSave}
               >
                 Save theme
-              </button>
+              </Button>
             </div>
           </div>
 
diff --git a/src/app/components/ThemeToggle.module.css b/src/app/components/ThemeToggle.module.css
deleted file mode 100644
index 891b69d..0000000
--- a/src/app/components/ThemeToggle.module.css
+++ /dev/null
@@ -1,21 +0,0 @@
-.toggle {
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 32px;
-  height: 32px;
-  padding: 0;
-  border: var(--border-width) solid transparent;
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text-secondary);
-  cursor: pointer;
-  transition:
-    background var(--dur-fast) var(--ease),
-    color var(--dur-fast) var(--ease);
-}
-
-.toggle:hover {
-  background: var(--layer-02);
-  color: var(--text);
-}
diff --git a/src/app/components/ThemeToggle.tsx b/src/app/components/ThemeToggle.tsx
index 6d1b509..8314822 100644
--- a/src/app/components/ThemeToggle.tsx
+++ b/src/app/components/ThemeToggle.tsx
@@ -7,14 +7,14 @@
  * persisted `ui.theme` key directly — no separate Appearance control to sync.
  *
  * The button shows the icon of the theme you'll switch *to* (moon when light,
- * sun when dark) and labels itself for screen readers. The focus ring comes from
- * the shared rule in base.css; chart + editor follow the theme via their own
- * store subscriptions, so flipping the store repaints everything.
+ * sun when dark) and labels itself for screen readers. Chart + editor follow the
+ * theme via their own store subscriptions, so flipping the store repaints
+ * everything.
  */
 
 import { useAppStore } from '../stores/AppStore';
 import { Icon } from './Icon';
-import styles from './ThemeToggle.module.css';
+import { IconButton } from './IconButton';
 
 export function ThemeToggle() {
   const uiTheme = useAppStore((s) => s.uiTheme);
@@ -22,18 +22,16 @@ export function ThemeToggle() {
   const target = uiTheme === 'dark' ? 'light' : 'dark';
 
   return (
-    <button
-      type="button"
-      className={styles.toggle}
+    <IconButton
       onClick={toggleTheme}
       // Toggle button with a stable name + pressed state (APG; doc §10.6): AT
       // announces the *current* theme ("Dark theme, pressed"), at parity with the
       // icon a sighted user sees — not just the action. `title` keeps the hover hint.
       aria-pressed={uiTheme === 'dark'}
-      aria-label="Dark theme"
+      label="Dark theme"
       title={`Switch to ${target} theme`}
     >
       {uiTheme === 'dark' ? <Icon name="sun" size="md" /> : <Icon name="moon" size="md" />}
-    </button>
+    </IconButton>
   );
 }
diff --git a/src/app/components/Toaster.module.css b/src/app/components/Toaster.module.css
index 3553745..4ac4dc3 100644
--- a/src/app/components/Toaster.module.css
+++ b/src/app/components/Toaster.module.css
@@ -146,6 +146,10 @@
   margin-top: var(--space-3);
 }
 
+/* Deliberately NOT the Button primitive: the action is coloured by the toast's
+   kind (--toast-accent border/label) and sits below the control scale —
+   content-sized inside an already-compact toast, like the inline link-style
+   actions (arch 09 §4). */
 .action {
   padding: var(--space-1) var(--space-3);
   font: inherit;
@@ -167,29 +171,7 @@
   outline-offset: 2px;
 }
 
+/* Dismiss is the shared IconButton (sm); the class is a layout marker only. */
 .close {
   flex: none;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-  width: 24px;
-  height: 24px;
-  padding: 0;
-  border: none;
-  border-radius: var(--radius);
-  background: transparent;
-  color: var(--text-secondary);
-  font-size: 12px;
-  cursor: pointer;
-  transition: background var(--dur-fast) var(--ease);
-}
-
-.close:hover {
-  background: var(--layer-01);
-  color: var(--text);
-}
-
-.close:focus-visible {
-  outline: 2px solid var(--focus);
-  outline-offset: 2px;
 }
diff --git a/src/app/components/Toaster.tsx b/src/app/components/Toaster.tsx
index d6df57c..ecbac16 100644
--- a/src/app/components/Toaster.tsx
+++ b/src/app/components/Toaster.tsx
@@ -24,6 +24,7 @@ import {
   type NotificationKind,
 } from '../stores/NotificationStore';
 import { Icon, type IconName } from './Icon';
+import { IconButton } from './IconButton';
 import styles from './Toaster.module.css';
 
 /** Auto-dismiss delay for the non-critical kinds (ms). Errors/warnings persist. */
@@ -115,14 +116,14 @@ function Toast({
           </div>
         )}
       </div>
-      <button
-        type="button"
+      <IconButton
+        size="sm"
         className={styles.close}
-        aria-label="Dismiss notification"
+        label="Dismiss notification"
         onClick={handleDismiss}
       >
         <Icon name="close" />
-      </button>
+      </IconButton>
     </div>
   );
 }
diff --git a/styles/tokens.css b/styles/tokens.css
index 17e7ed2..ce4e478 100644
--- a/styles/tokens.css
+++ b/styles/tokens.css
@@ -39,6 +39,14 @@
   /* Layout */
   --header-height: 48px;
 
+  /* Control scale (arch 09 §4) — every interactive control is one of exactly two
+     heights. 32px is THE control height: buttons, inputs, selects, segmented
+     controls, icon buttons — anything that sits in a toolbar or form row. 40px is
+     reserved for standalone primary CTAs (e.g. the library's Build Chart) and
+     modal footers. No other control heights exist; a third value is drift. */
+  --control-height: 32px;
+  --control-height-lg: 40px;
+
   /* Motion — productive only; neutralized under prefers-reduced-motion in base.css */
   --dur-fast: 70ms;
   --dur-fast-2: 110ms;