diff --git a/CONTRIBUTOR-DOCS/03_project-planning/03_components/README.md b/CONTRIBUTOR-DOCS/03_project-planning/03_components/README.md
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--- a/CONTRIBUTOR-DOCS/03_project-planning/03_components/README.md
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@@ -27,12 +27,15 @@
 - Asset
     - [Asset migration roadmap](asset/rendering-and-styling-migration-analysis.md)
 - Avatar
+    - [Avatar accessibility migration analysis](avatar/accessibility-migration-analysis.md)
+    - [Avatar — 2nd-Gen Migration Plan](avatar/migration-plan.md)
     - [Avatar accessibility migration analysis](avatar/rendering-and-styling-migration-analysis.md)
 - Badge
     - [Badge accessibility migration analysis](badge/accessibility-migration-analysis.md)
     - [Badge migration roadmap](badge/rendering-and-styling-migration-analysis.md)
 - Button
     - [Button accessibility migration analysis](button/accessibility-migration-analysis.md)
+    - [Button Migration Plan](button/migration-plan.md)
     - [Button migration roadmap](button/rendering-and-styling-migration-analysis.md)
 - Button Group
     - [Button Group migration roadmap](button-group/rendering-and-styling-migration-analysis.md)
diff --git a/CONTRIBUTOR-DOCS/03_project-planning/03_components/button/migration-plan.md b/CONTRIBUTOR-DOCS/03_project-planning/03_components/button/migration-plan.md
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@@ -0,0 +1,608 @@
+<!-- Generated breadcrumbs - DO NOT EDIT -->
+
+[CONTRIBUTOR-DOCS](../../../README.md) / [Project planning](../../README.md) / [Components](../README.md) / Button / Button Migration Plan
+
+<!-- Document title (editable) -->
+
+# Button Migration Plan
+
+<!-- Generated TOC - DO NOT EDIT -->
+
+<details open>
+<summary><strong>In this doc</strong></summary>
+
+- [TL;DR](#tldr)
+    - [Most blocking open questions](#most-blocking-open-questions)
+- [1st-gen API surface](#1st-gen-api-surface)
+    - [Properties / attributes](#properties--attributes)
+    - [Methods](#methods)
+    - [Events](#events)
+    - [Slots](#slots)
+    - [CSS custom properties](#css-custom-properties)
+    - [Shadow DOM output (rendered HTML)](#shadow-dom-output-rendered-html)
+- [Dependencies](#dependencies)
+- [Changes overview](#changes-overview)
+    - [Must ship — breaking or a11y-required](#must-ship--breaking-or-a11y-required)
+    - [Additive — ships when ready, zero breakage for consumers already on 2nd-gen](#additive--ships-when-ready-zero-breakage-for-consumers-already-on-2nd-gen)
+- [2nd-gen API decisions](#2nd-gen-api-decisions)
+    - [Public API](#public-api)
+    - [Behavioral semantics](#behavioral-semantics)
+    - [Pending accessible-name rule (2nd-gen)](#pending-accessible-name-rule-2nd-gen)
+    - [Accessibility semantics notes (2nd-gen)](#accessibility-semantics-notes-2nd-gen)
+    - [Deferred semantics note (2nd-gen)](#deferred-semantics-note-2nd-gen)
+    - [Internal semantic button implications](#internal-semantic-button-implications)
+- [Architecture: core vs SWC split](#architecture-core-vs-swc-split)
+    - [Shared semantics reuse](#shared-semantics-reuse)
+    - [Global alignment contract](#global-alignment-contract)
+- [Migration checklist](#migration-checklist)
+    - [Preparation (this ticket)](#preparation-this-ticket)
+    - [Setup](#setup)
+    - [API](#api)
+    - [Styling](#styling)
+    - [Accessibility](#accessibility)
+    - [Testing](#testing)
+    - [Documentation](#documentation)
+    - [Review](#review)
+- [Blockers and open questions](#blockers-and-open-questions)
+    - [Deferred follow-up tickets](#deferred-follow-up-tickets)
+- [References](#references)
+
+</details>
+
+<!-- Document content (editable) -->
+
+> **SWC-1873** · Planning output. Must be reviewed before implementation begins.
+
+---
+
+## TL;DR
+
+- `sp-button` is planned to become button-only in 2nd-gen; deprecated link mode moves to native `<a>` with global button styling
+- 2nd-gen `sp-button` should render an internal semantic `<button>` and move semantics off the host
+- Pending must remain focusable while unavailable, use `aria-disabled="true"`, and announce a descriptive busy state
+- The visual API should use React-aligned `fillStyle` terminology: `primary` / `secondary` support `fill` + `outline`; `accent` / `negative` are fill-only
+- Pending will use a 1-second delayed inline animated SVG spinner in the initial migration; reuse can be evaluated later
+- Component Button styles and [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css) should share source/imports if possible
+- `core` should own reusable semantic rules and serve as the intended reuse base for later button-like migrations; `swc` should own `sp-button` rendering and S2 styling
+
+### Most blocking open questions
+
+None currently.
+
+---
+
+## 1st-gen API surface
+
+**Source:** [`1st-gen/packages/button/src/Button.ts`](../../../../1st-gen/packages/button/src/Button.ts)
+**Version:** `@spectrum-web-components/button@1.11.2`
+**Custom element tag:** `sp-button`
+
+### Properties / attributes
+
+| Property | Type | Default | Attribute | Notes |
+|---|---|---|---|---|
+| `variant` | `'accent' \| 'primary' \| 'secondary' \| 'negative' \| 'white' \| 'black' \| 'cta' \| 'overBackground'` | `'accent'` | `variant` | Invalid values are coerced to `accent`. `cta`, `overBackground`, `white`, and `black` are already deprecated aliases. |
+| `staticColor` | `'white' \| 'black' \| undefined` | `undefined` | `static-color` | Can coexist with `variant`. Used for over-background styling. |
+| `treatment` | `'fill' \| 'outline'` | `'fill'` | `treatment` | Visual treatment. |
+| `quiet` | `boolean` | `false` | `quiet` | Alias for `treatment="outline"`; not reflected back to the attribute when set programmatically. |
+| `size` | `'s' \| 'm' \| 'l' \| 'xl'` | no explicit default from `SizedMixin` | `size` | `Button` uses `SizedMixin(..., { noDefaultSize: true })`; CSS treats missing size as medium styling. |
+| `pending` | `boolean` | `false` | `pending` | Disables interaction and swaps accessible label to pending text while active. |
+| `pendingLabel` | `string` | `'Pending'` | `pending-label` | Temporary accessible name used during pending state. |
+| `noWrap` | `boolean` | `false` | `no-wrap` | 1st-gen off-spec escape hatch to disable wrapping; candidate for rename in 2nd-gen. |
+| `active` | `boolean` | `false` | `active` | Reflected pressed-state flag used during keyboard interaction. |
+| `type` | `'button' \| 'submit' \| 'reset'` | `'button'` | `type` | Submit/reset is proxied through a temporary native `<button>`. |
+| `disabled` | `boolean` | `false` | `disabled` | Inherited from `Focusable`; manages tabindex and `aria-disabled`. |
+| `autofocus` | `boolean` | `false` | `autofocus` | Inherited from `Focusable`. |
+| `tabIndex` | `number` | managed | `tabindex` | Inherited from `Focusable`; host is the focus target. |
+| `label` | `string \| undefined` | `undefined` | `label` | Inherited from `LikeAnchor`; mirrored to host `aria-label`. Primary accessible-name API for icon-only usage. |
+| `href` | `string \| undefined` | `undefined` | `href` | Deprecated link mode. Causes host role to change from button to link. |
+| `target` | `'_blank' \| '_parent' \| '_self' \| '_top' \| undefined` | `undefined` | `target` | Deprecated with `href`. |
+| `download` | `string \| undefined` | `undefined` | `download` | Deprecated with `href`. |
+| `referrerpolicy` | string union | `undefined` | `referrerpolicy` | Deprecated with `href`. |
+| `rel` | `string \| undefined` | `undefined` | `rel` | Deprecated with `href`. |
+| `icon-only` | `boolean` | `false` | `icon-only` | Attribute-only styling hook used in README, stories, tests, and CSS; no declared TS property. |
+
+### Methods
+
+| Method | Signature | Notes |
+|---|---|---|
+| `click()` | `(): void` | No-op while `pending`; otherwise delegates to `Focusable.click()`, including link and submit/reset proxy behavior. |
+
+### Events
+
+No custom events. Consumers rely on native `click`.
+
+### Slots
+
+| Slot | Content | Notes |
+|---|---|---|
+| default | Visible button label | Observed via `ObserveSlotText` to determine whether a label is present. |
+| `icon` | Leading icon | Slot receives an `icon-only` flag when no default-slot label content is present. |
+
+### CSS custom properties
+
+The 1st-gen implementation exposes a large legacy customization surface through imported [`button-base.css`](../../../../1st-gen/packages/button/src/button-base.css), [`spectrum-button.css`](../../../../1st-gen/packages/button/src/spectrum-button.css), and [`button-overrides.css`](../../../../1st-gen/packages/button/src/button-overrides.css). In practice this includes:
+
+- Many `--mod-button-*` variables for sizing, spacing, color, border, and focus ring
+- Legacy `--spectrum-button-*` token fallback chains
+- High-contrast `--highcontrast-button-*` overrides
+- Progress-circle passthroughs such as `--mod-progress-circle-position`
+
+This full modifier surface will not be carried forward to 2nd-gen.
+
+### Shadow DOM output (rendered HTML)
+
+```html
+<!-- Default button mode: the host itself behaves as the interactive control -->
+<slot name="icon" icon-only></slot>
+<span id="label">
+  <slot></slot>
+</span>
+<sp-progress-circle
+  id="loader"
+  size="s"
+  indeterminate
+  class="progress-circle"
+  role="presentation"
+></sp-progress-circle>
+
+<!-- Link mode: same content plus a hidden proxy anchor -->
+<slot name="icon"></slot>
+<span id="label">
+  <slot></slot>
+</span>
+<a
+  id="button"
+  class="button anchor"
+  href="..."
+  tabindex="-1"
+  aria-hidden="true"
+></a>
+```
+
+---
+
+## Dependencies
+
+| Package | Version | Role |
+|---|---|---|
+| `@spectrum-web-components/base` | `1.11.2` | `LitElement` base utilities, decorators, `SizedMixin` |
+| `@spectrum-web-components/shared` | `1.11.2` | `Focusable`, `LikeAnchor`, and `ObserveSlotText` behaviors |
+| `@spectrum-web-components/reactive-controllers` | `1.11.2` | `PendingStateController` and pending `aria-label` caching |
+| `@spectrum-web-components/progress-circle` | `1.11.2` | Pending-state indicator |
+| `@spectrum-web-components/icon` / consumer-provided icons | `1.11.2` | Optional slotted icon content |
+
+---
+
+## Changes overview
+
+> **Priority framing:**
+> - **Accessibility is non-negotiable** — all a11y requirements ship as part of this migration.
+> - **Breaking changes** are assessed on merit — some must ship now to avoid a second, more disruptive migration event later.
+> - **Additive changes** can be deferred and will not cause consumer breakage when they do ship.
+
+### Must ship — breaking or a11y-required
+
+#### API and naming
+
+| # | What changes | 1st-gen behavior | 2nd-gen behavior | Consumer migration path |
+|---|---|---|---|---|
+| **B1** | Remove link API from `sp-button` | `href` and related anchor attrs turn the host into a link-like control, but this mode is already deprecated in docs and runtime warnings. | `sp-button` is button-only. Navigation uses native `<a>` with global button styles, not `sp-button`. | Replace `<sp-button href="...">` with native `<a class="swc-Button ...">` or equivalent global-element styling. |
+| **B2** | Align visual API names to the confirmed Design source of truth and React terminology | 1st-gen uses `primary`, `secondary`, `accent`, `negative`, deprecated color aliases, `quiet`, and `treatment`. | 2nd-gen visual API should use `primary`, `secondary`, `accent`, and `negative`, plus static white/black combinations where shown, and prefer React-aligned `fillStyle` terminology instead of `treatment`. | Migrate deprecated `variant` values to canonical `variant` + `static-color` + `fill-style` combinations. |
+| **B3** | Collapse legacy host-managed semantics into native internal control | 1st-gen host manages `role`, `tabindex`, keyboard handling, click proxying, and submit/reset proxy behavior itself. | 2nd-gen should prefer a real internal `<button>` for semantics and keyboard behavior, with host API mapping onto that internal control. | Consumer markup usually stays the same, but any shadow DOM poking or role/tabindex assertions must be updated. |
+| **B4** | Remove `--mod-*` customization surface | Consumers can override many colors, sizes, and spacings through legacy modifier chains. | 2nd-gen exposes only reviewed `--swc-*` component-level properties, if any. | Migrate custom styling to supported `--swc-*` properties or wrapper-level CSS. |
+
+#### Styling and visuals
+
+| # | What changes | 1st-gen behavior | 2nd-gen behavior | Consumer migration path |
+|---|---|---|---|---|
+| **B5** | Restrict treatment/style combinations to those present in Design/Figma | 1st-gen exposes outline and static combinations broadly, and `quiet` can alias to outline on any variant. | 2nd-gen should only ship the confirmed combinations: fill + outline for `primary` and `secondary`; fill-only for `accent` and `negative`; static white/black only for the primary/secondary families shown in Design/Figma. | Audit any unsupported combinations and migrate them to the nearest supported equivalent. |
+| **B6** | Resolve static white outline contrast bug (`SWC-1139`) | The static white outline variant can be shown over backgrounds where hover-state contrast between white text/border and the background is insufficient. | When rendering the static white outline button in 2nd-gen docs/stories/examples, it must be paired with a background color that preserves required contrast on hover. The migration should treat this as a must-ship a11y/visual correctness requirement, not an optional docs polish item. | Update examples, stories, and visual regression fixtures so static white outline is only demonstrated on approved backgrounds. |
+
+#### Accessibility and behavior
+
+| # | What changes | 1st-gen behavior | 2nd-gen behavior | Consumer migration path |
+|---|---|---|---|---|
+| **B7** | Resolve pending-state accessibility bug (`SWC-459`) | Pending currently blocks activation, but the accessibility contract is incomplete: assistive tech is not clearly told the control is unavailable, the default pending label is too generic (`"Pending"`), and high-contrast presentation does not fully communicate the disabled/unavailable state. | Pending in 2nd-gen must expose unavailable state to assistive tech, use a more descriptive default accessible label than bare `"Pending"`, and render with disabled high-contrast styling because the control cannot be activated while pending. | Consumers using custom `pending-label` values may need to update wording to the new recommended pattern. |
+| **B8** | Preserve host `visibility` behavior on the label (`SWC-701`) | The button label can manage its own visibility in a way that breaks host-level `visibility: hidden`, leaving label text visible when the host is hidden. | In 2nd-gen, the label must inherit visibility from the host, or avoid setting its visibility separately, so host-level hiding hides the entire control consistently. | Consumers relying on `visibility: hidden` at the host level should see the bug resolved without markup changes. |
+| **B9** | Replace box-shadow focus ring with outline for truncated buttons (`SWC-886`) | Truncated buttons need `overflow: hidden`, which can clip a box-shadow-based focus ring. | 2nd-gen focus indication must use `outline` / `outline-offset` so focus remains visible even when truncation requires clipped overflow. | No consumer markup change expected; visual/focus behavior improves automatically. |
+| **B10** | Defer form-associated `submit` / `reset` behavior from the initial 2nd-gen Button scope | 1st-gen proxies `submit` / `reset` through a temporary light-DOM native `<button>`. | Initial 2nd-gen Button scope should default to button semantics only while form-associated behavior is deferred pending an ElementInternals/tooling recommendation. | Consumers needing `submit` / `reset` should continue using native buttons/global styles or stay on 1st-gen behavior until the follow-up lands. |
+
+### Additive — ships when ready, zero breakage for consumers already on 2nd-gen
+
+| # | What is added | Notes |
+|---|---|---|
+| **A1** | Explicit, documented `--swc-button-*` properties | Only expose properties justified by the CSS custom-property guide; do not recreate the old modifier matrix. |
+| **A2** | Playwright accessibility snapshots for pending and icon-only states | These strengthen regression coverage without changing the public API. |
+| **A3** | Future support for cross-root ARIA mapping | Deferred to `SWC-2033` while the cross-root semantics approach is evaluated. |
+| **A4** | Future support for form-associated `submit` / `reset` | Deferred to `SWC-2034` until the ElementInternals/tooling path is settled. |
+| **A5** | Host `focus` / `blur` compatibility parity | Deferred to `SWC-2035`; initial 2nd-gen Button will document `click` plus bubbling `focusin` / `focusout` as the supported host-listener contract. |
+| **A6** | React Spectrum-only `genai` and `premium` variants | Deferred to `SWC-2036` because they are not part of the approved baseline Button scope in this plan. |
+
+---
+
+## 2nd-gen API decisions
+
+These are derived from the 1st-gen implementation, current deprecations, the Figma Desktop button spec, and the rendering roadmap. For visual API, Figma is the source of truth. Confirmed items are marked; deferred follow-up work is tracked in [Blockers and open questions](#blockers-and-open-questions).
+
+**Scope note:** this plan is for `sp-button` only. `sp-clear-button` and `sp-close-button` live in the same package today, but they are intentionally out of scope for this migration plan and should not block the core `sp-button` migration.
+
+### Public API
+
+#### Properties / attributes (2nd-gen)
+
+| Property | Type | Default | Attribute | Notes |
+|---|---|---|---|---|
+| `size` | `'s' \| 'm' \| 'l' \| 'xl'` | `'m'` | `size` | **Confirmed.** Keep existing T-shirt size scale. |
+| `variant` | `'primary' \| 'secondary' \| 'accent' \| 'negative'` | `'primary'` | `variant` | **Confirmed by Design.** Use `primary`; Figma's `default` naming was a typo. React-only `premium` and `genai` variants are deferred to `SWC-2036`. |
+| `fillStyle` | `'fill' \| 'outline'` | `'fill'` | `fill-style` | **Confirmed.** Use React-aligned terminology. `outline` is only spec-backed for `primary` and `secondary` families, including their static white/black equivalents. Migrate legacy `treatment` usage to `fill-style`. |
+| `staticColor` | `'white' \| 'black' \| undefined` | `undefined` | `static-color` | **Confirmed.** Static color is only spec-backed with the `primary` and `secondary` families shown in Design/Figma. |
+| `disabled` | `boolean` | `false` | `disabled` | **Confirmed.** Maps to native disabled behavior on the internal button. |
+| `pending` | `boolean` | `false` | `pending` | **Confirmed.** Keep public API; while pending, the button remains focusable but is otherwise unavailable. |
+| `pendingLabel` | `string` | derived from the resolved non-busy accessible name + busy suffix | `pending-label` | **Adjusted for `SWC-459`.** Distinct from the control name; overrides the default busy-state announcement when supplied. |
+| `type` | deferred beyond initial scope | `'button'` | maybe none / future | **Deferred.** Initial 2nd-gen Button should behave as a regular button; `submit` / `reset` are future work. |
+| `label` | deprecated | n/a | `label` | **Planned removal.** Prefer visible text and `aria-label` to avoid ambiguity with `pending-label`. |
+| `iconOnly` | `boolean` | `false` | `icon-only` | **Proposed.** Keep for backwards compatibility and styling clarity, even if some detection can be automatic. |
+| `truncate` | `boolean` | `false` | `truncate` | **Confirmed rename.** Replaces legacy `no-wrap` with a more explicit name for the actual behavior: single-line truncation with overflow handling rather than wrapping. Tooltip guidance for clipped content is documentation guidance, not built-in Button behavior. |
+| `active` | internal styling state | n/a | maybe none / internal only | **Proposed.** Do not preserve as a documented consumer-controlled API unless styling proves it necessary. |
+| `href`, `target`, `download`, `referrerpolicy`, `rel` | removed | n/a | removed | **Confirmed removal.** Use native anchors for navigation. |
+
+#### Visual matrix (2nd-gen)
+
+Based on the attached spec, the supported visual combinations should be planned as:
+
+| Visual family | Fill | Outline | Static white | Static black |
+|---|---|---|---|---|
+| `primary` | Yes | Yes | Yes | Yes |
+| `secondary` | Yes | Yes | Yes | Yes |
+| `accent` | Yes | No | No | No |
+| `negative` | Yes | No | No | No |
+
+Additional Figma-confirmed presentation modes:
+
+- Label only
+- Icon + label
+- Icon only
+- Text wrap
+- Truncate
+- Pending
+- Disabled
+- Hover
+
+#### Slots (2nd-gen)
+
+| Slot | Content | Notes |
+|---|---|---|
+| default | Visible button label | **Confirmed.** |
+| `icon` | Leading icon | **Confirmed.** Keep the existing named slot. |
+
+#### CSS custom properties (2nd-gen)
+
+No `--mod-*` properties will be exposed. New `--swc-*` component-level properties may be introduced where needed — these are additive and not breaking. See [Component Custom Property Exposure](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/02_custom-properties.md#component-custom-property-exposure) for what to expose and how.
+
+Initial expectation for Button is a small reviewed set.
+
+### Behavioral semantics
+
+### Pending accessible-name rule (2nd-gen)
+
+Pending-state naming should resolve in this order:
+
+1. `pending-label`
+2. Resolved non-busy accessible name + busy suffix
+3. Fixed fallback such as `"Busy"`
+
+The resolved non-busy accessible name should come from the same sources used for the control itself, e.g. `aria-label` or visible text. Default wording should use the reviewed `busy` suffix pattern, e.g. `"Save, busy"`.
+
+### Accessibility semantics notes (2nd-gen)
+
+- the internal native `<button>` should be the semantic control and primary tab stop
+- the host should not duplicate `role="button"` semantics when an internal button already exists
+- host-facing naming APIs must be intentionally mapped to the internal control; full cross-root `aria-labelledby` / `aria-describedby` support is deferred
+- pending should remain button semantics; it should not expose progressbar semantics unless it truly represents measurable progress
+- pending announcements should rely on accessible-name updates, not a built-in polite status region; when broader status communication matters, consumers can add a toast or external status region rather than having individual controls post competing messages
+
+### Deferred semantics note (2nd-gen)
+
+Cross-root `aria-labelledby` / `aria-describedby` support and form-associated `submit` / `reset` behavior are deferred beyond the initial Button migration scope. They depend on a clearer ElementInternals/platform/tooling recommendation and should not block the first 2nd-gen Button release.
+
+### Internal semantic button implications
+
+Using an internal semantic `<button>` also means:
+
+- the internal button is the semantic source of truth for button role, focus, and disabled behavior
+- host-level button semantics must not compete with the internal button
+- the host should not remain the primary tab stop when the internal native button is present
+- host `disabled` reflects API state, while the internal `<button disabled>` enforces native disabled behavior
+- pending should not use native `disabled` on the internal button if focusability must be preserved
+- host `aria-label` and other button-relevant semantics should be forwarded intentionally, not assumed
+- native button keyboard/click behavior should be reused where possible rather than reimplemented on the host
+- host listeners should continue to observe native `click` and bubbling `focusin` / `focusout` from the internal control; host-level `focus` / `blur` parity is deferred and may require custom events if the team decides that compatibility is necessary
+
+---
+
+## Architecture: core vs SWC split
+
+> The 1st-gen component is a **reference only** — 2nd-gen is built independently. Neither generation imports from the other.
+
+Follow the [Badge migration reference](../../02_workstreams/02_2nd-gen-component-migration/02_step-by-step/01_washing-machine-workflow.md#reference-badge-migration) as the concrete pattern for the core/SWC split.
+
+| Layer | Path | Contains |
+|---|---|---|
+| **Core** | `2nd-gen/packages/core/components/button/` | `Button.base.ts`, `Button.types.ts`, validation, state, accessible-name logic, attribute forwarding, pending-label behavior, and other reusable semantic rules. No rendering. |
+| **SWC** | `2nd-gen/packages/swc/components/button/` | `Button.ts`, `button.css`, element registration, stories, tests, and the specific S2 rendering/styling for `sp-button`. |
+
+Planned rendering shape:
+
+- Core owns API normalization and warnings
+- SWC renders a real internal control with `.swc-Button`
+- Preferred internal DOM is a native `<button>` plus icon/label/pending children
+- If navigation is removed as planned, no anchor render path is needed in 2nd-gen `sp-button`
+- The component stylesheet and [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css) should share source/imports if possible so button-styled global elements stay visually in sync with the component
+- The current contents of [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css) are temporary POC scaffolding, not a locked design contract; they may be fully replaced during the Button migration as long as the resulting global-element API stays aligned with the component
+- New focus primitives from [PR #6129](https://github.com/adobe/spectrum-web-components/pull/6129) are informative for disabled/focus behavior, but are not currently planned as direct Button dependencies
+- `DisabledMixin` may be evaluated during implementation for true `disabled` state only; it does not replace Button's custom `pending` behavior, which must remain focusable
+
+### Shared semantics reuse
+
+Button should establish a reusable semantic foundation in `core`, but not a shared rendered DOM.
+
+The goal is for later button-like components such as `ActionButton`, `ClearButton`, `CloseButton`, `PickerButton`, and `InfieldButton` to reuse the same semantic rules without inheriting `sp-button`'s rendered structure or visual API. This Button `core` layer is the intended reuse base for those later migrations.
+
+Reusable `core` concerns:
+
+- public property validation and normalization for button-like state
+- accessible-name resolution and pending-label fallback rules
+- host-to-internal-button attribute forwarding rules
+- `disabled` vs `pending` behavior rules
+- future form-associated button policy once the platform/tooling path is settled
+- shared interaction guards such as activation suppression while pending
+
+Non-reusable `swc` concerns:
+
+- internal DOM shape and slot layout
+- icon placement and chevron/clear/close affordances
+- pending indicator rendering
+- variant, fill-style, size, and static-color styling
+- component-specific wrappers such as in-field layouts
+
+Lightweight example:
+
+```ts
+// core/components/button/Button.base.ts
+export abstract class ButtonBase extends SpectrumElement {
+  protected getResolvedAccessibleName(): string | null {
+    // derive from aria-label or visible text
+  }
+
+  protected getPendingAccessibleName(): string {
+    // derive from pending-label or the resolved non-busy name
+  }
+
+  protected getForwardedButtonAttributes(): Record<string, string | boolean> {
+    // return disabled/aria-disabled/type/aria-* mapping for the inner control
+  }
+}
+
+// swc/components/button/Button.ts
+// renders the internal <button> and applies the shared semantic contract
+```
+
+This keeps the 2nd-gen `core` / `swc` split intact: `core` owns semantic behavior, while each downstream SWC component can render its own control and styling on top of that shared contract.
+
+### Global alignment contract
+
+Button component styles and global button styles must align on:
+
+- visual family names: `primary`, `secondary`, `accent`, `negative`
+- fill-style model and allowed combinations
+- static color support and restrictions
+- size mappings and core token usage
+- focus-ring and truncation behavior
+- exposed `--swc-button-*` custom properties
+
+Allowed differences:
+
+- global styles support only native-element-compatible states
+- native links do not support component-only states such as `pending` or `disabled`
+- component-internal accessibility wiring does not need a global equivalent
+
+---
+
+## Migration checklist
+
+### Preparation (this ticket)
+
+- [x] 1st-gen API surface documented
+- [x] Dependencies identified
+- [x] Breaking changes documented
+- [x] 2nd-gen API decisions drafted
+- [ ] Plan reviewed by at least one other engineer
+
+### Setup
+
+- [ ] Create `2nd-gen/packages/core/components/button/`
+- [ ] Create `2nd-gen/packages/swc/components/button/`
+- [ ] Wire exports in both `package.json` files
+- [ ] Implement Button styles so the component stylesheet and [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css) share source/imports if practical
+- [ ] Treat the current [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css) implementation as replaceable POC code, not as the canonical source of Button styling
+- [ ] Check out `spectrum-css` at `spectrum-two` branch as sibling directory
+
+### API
+
+#### Naming and public surface
+
+- [ ] `Button.types.ts`: define canonical `ButtonVariant`, `ButtonFillStyle`, `ButtonStaticColor`, and `ButtonSize`
+- [ ] `Button.base.ts`: retain `size`, `variant`, `fillStyle`, `staticColor`, `disabled`, `pending`, `pendingLabel`, and accessible-name handling
+- [ ] Rename legacy `noWrap` to `truncate` in the 2nd-gen API
+- [ ] Remove `label` in favor of `aria-label`
+- [ ] Remove deprecated link API (`href`, `target`, `download`, `referrerpolicy`, `rel`) from the 2nd-gen public surface
+- [ ] Remove deprecated `variant` aliases (`cta`, `overBackground`, `white`, `black`)
+- [ ] Do not carry forward `quiet` as a 2nd-gen visual API; document migration to explicit `fill-style="outline"` where the Figma matrix allows it
+- [ ] Document migration from `no-wrap` to `truncate`
+
+#### Semantics and forms
+
+- [ ] Define which host attributes/semantics are forwarded to the internal button and which remain host-only
+- [ ] When `pending`, expose unavailable state to assistive tech via `aria-disabled="true"` even when the button is not otherwise `disabled` (`SWC-459`)
+- [ ] Replace the default pending accessible label with a descriptive busy-state pattern derived from the resolved non-busy accessible name, while still allowing `pending-label` override (`SWC-459`)
+- [ ] Keep semantic helpers reusable in `core` so later button-like components can share behavior without sharing `sp-button` DOM or styling
+- [ ] Do not recreate proxy patterns where the host carries button semantics while a different hidden internal control handles real activation
+- [ ] Document `submit` / `reset` and cross-root ARIA mapping as deferred follow-up work rather than initial Button scope
+- [ ] Preserve host-listener support for native `click` and bubbling `focusin` / `focusout` from the internal control
+- [ ] Document host-level `focus` / `blur` parity as deferred unless the team decides custom events are needed for compatibility
+
+#### Alignment checks
+
+- [x] Use React-aligned `fillStyle` terminology instead of `treatment`
+- [x] Defer React Spectrum-only variants such as `premium` and `genai` to follow-up work (`SWC-2036`)
+
+### Styling
+
+> Follow the [CSS style guide](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/) as the source of truth for all styling work. Key references: [migration steps](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/04_spectrum-swc-migration.md), [custom properties](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/02_custom-properties.md), [anti-patterns](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/05_anti-patterns.md).
+
+- [ ] Add `.swc-Button` to the internal semantic `<button>` in `render()`; keep styling off `:host`
+- [ ] Copy S2 source from `spectrum-css` `spectrum-two` branch `index.css` (not `/dist`) into `button.css` as baseline
+
+#### Shared source and drift prevention
+
+- [ ] Reconcile the component stylesheet with existing [`global-button.css`](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css)
+- [ ] Prefer a shared-source/import strategy for component and global button styles; if styles must be copied, treat the migrated component stylesheet as the source of truth and document the sync mechanism and drift risks in the implementation notes
+- [ ] Fully override or replace the current global button POC styles where needed to match the migrated Button implementation
+- [ ] Update class and custom property prefixes from `.spectrum-` to `.swc-`; remove all `--mod-*` and `--spectrum-*` fallback chains
+
+#### Visual model and regressions
+
+- [ ] Migrate icon-only, truncate (previously noWrap), size, static-color, and outline fill-style selectors
+- [ ] Implement truncation behavior explicitly, not just `white-space: nowrap`; confirm overflow ellipsis treatment in S2 CSS
+- [ ] Ensure the button label inherits host visibility, or otherwise does not override it, so `visibility: hidden` on the host hides the label too (`SWC-701`)
+- [ ] Restrict accent and negative styling to fill-only combinations
+- [ ] Restrict static white/black styling to the primary and secondary families shown in Design/Figma
+- [ ] For `static-color="white"` + `fill-style="outline"`, define and document approved background color usage so hover-state contrast remains sufficient (`SWC-1139`)
+- [ ] Use `outline` / `outline-offset` for focus indication rather than `box-shadow`, especially where truncation requires `overflow: hidden` (`SWC-886`)
+- [ ] Replace legacy pending indicator styling with the agreed 1-second delayed inline animated SVG spinner
+- [ ] Verify i18n size modifiers (`:lang(ja)`, `:lang(ko)`, `:lang(zh)`) if present in S2 source
+- [ ] Pass stylelint (property order, `no-descending-specificity`, token validation)
+
+### Accessibility
+
+#### Naming and semantics
+
+- [ ] Align Button implementation with the approved `accessibility-migration-analysis.md`
+- [ ] Ensure icon-only usage has a reliable accessible name via `aria-label`
+- [ ] Pending state must set `aria-disabled="true"` because the control cannot be activated while pending (`SWC-459`)
+- [ ] Pending state must use a descriptive default accessible label based on the resolved non-busy accessible name plus a busy suffix, not bare `"Pending"` (`SWC-459`)
+- [ ] Pending state must be announced to screen readers, even if the final implementation uses more than just an accessible-name change
+- [ ] Pending state must remain focusable while otherwise unavailable, matching current React Spectrum behavior
+- [ ] Ensure host and internal button semantics do not conflict in the accessibility tree
+- [ ] Ensure the internal native button, not the host, is the semantic control exposed to assistive technology
+- [ ] Preserve keyboard activation for Space and Enter through native button semantics
+- [ ] Avoid duplicating native button activation logic on the host when the internal button already provides it
+- [ ] Forward host `aria-label` to the internal semantic button when that attribute is used
+
+#### State verification
+
+- [ ] Verify disabled state removes focusability and prevents interaction
+- [ ] Verify Windows High Contrast uses disabled/unavailable colors while pending (`SWC-459`)
+- [ ] Confirm host vs internal-control semantics in snapshots (`button` role, accessible name, disabled state)
+- [ ] Document the 1-second pending-spinner delay and whether reduced-motion treatment changes it
+
+### Testing
+
+- [ ] Port `1st-gen/packages/button/test/button.test.ts` coverage that still applies
+- [ ] Add Playwright `button.a11y.spec.ts` with `toMatchAriaSnapshot`
+
+#### Behavior
+
+- [ ] Add unit coverage for default `variant="primary"` behavior
+- [ ] Add unit coverage for pending accessible-name transitions, including the new default busy-label behavior (`SWC-459`)
+- [ ] Add unit/accessibility coverage for `aria-disabled="true"` while pending (`SWC-459`)
+- [ ] Add coverage proving pending buttons remain focusable while press and hover interactions are suppressed
+- [ ] Add unit coverage for icon-only accessible naming via `aria-label`
+- [ ] Add coverage proving host semantics do not duplicate or conflict with the internal button semantics
+- [ ] Add coverage proving the host is not the primary semantic/button focus target once the internal native button is present
+- [ ] Add coverage proving host listeners still observe native `click` and bubbling `focusin` / `focusout` behavior from the internal control
+- [ ] Add coverage proving host `visibility: hidden` also hides the button label (`SWC-701`)
+- [ ] Remove or replace tests that depend on deprecated `href` mode
+
+#### Visual regression
+
+- [ ] Add VRT coverage for size, variant, fill-style, static color, and pending combinations
+- [ ] Add visual regression coverage for static white outline on its approved background, including hover state (`SWC-1139`)
+- [ ] Add visual/high-contrast coverage for the pending state using disabled styling (`SWC-459`)
+- [ ] Add focus-visible regression coverage for truncated buttons so the ring is not clipped (`SWC-886`)
+
+### Documentation
+
+#### General
+
+- [ ] JSDoc on all public props, slots, and CSS custom properties
+- [ ] Storybook stories for primary, secondary, accent, negative, fill/outline where supported, icon-only, static colors, pending, disabled, and wrapping/truncate
+- [ ] Document that `quiet` is not part of the 2nd-gen visual API
+- [ ] Document the rename from `no-wrap` to `truncate` and its relationship to the spec’s wrapped-text presentation
+- [ ] Document the approved background treatment for static white outline examples so contrast is maintained on hover (`SWC-1139`)
+- [ ] Document pending-state accessibility behavior: `aria-disabled`, default busy-label pattern, and high-contrast disabled styling (`SWC-459`)
+- [ ] Document the initial host-listener contract: `click` and `focusin` / `focusout`; custom `focus` / `blur` events are not part of the initial Button scope and are deferred to `SWC-2035`
+- [ ] Document that 2nd-gen Button semantics and focus land on a real internal native `<button>`, not the custom-element host
+- [ ] Document supported naming APIs at the host level (`aria-label` and visible text) and how they map to the internal control
+- [ ] Document that cross-root `aria-labelledby` / `aria-describedby` and form-associated `submit` / `reset` are deferred follow-up work
+- [ ] Document that focus indication uses `outline` so it remains visible for truncated buttons (`SWC-886`)
+- [ ] Update global element guidance so button-styled native elements and `sp-button` describe the same visual API and any intentional limitations
+
+#### Breaking changes
+
+- [ ] Document breaking migration away from `href`
+- [ ] Document breaking migration from `treatment` to `fill-style`
+- [ ] Document migration away from deprecated variant aliases while preserving `primary` as the neutral family name
+- [ ] Document `label` removal in the API reference only
+
+### Review
+
+- [ ] `yarn lint:2nd-gen` passes (ESLint, Stylelint, Prettier)
+- [ ] Status table in workstream doc updated
+- [ ] PR created with description referencing SWC-1873
+- [ ] Peer engineer sign-off
+
+---
+
+## Blockers and open questions
+
+### Deferred follow-up tickets
+
+| Ticket | Deferred item | Why deferred | Related plan section |
+|---|---|---|---|
+| SWC-2033 | Cross-root ARIA support | Depends on a clearer cross-root semantics approach and should not block the initial Button migration. | [Additive](#additive--ships-when-ready-zero-breakage-for-consumers-already-on-2nd-gen), [Deferred semantics note (2nd-gen)](#deferred-semantics-note-2nd-gen) |
+| SWC-2034 | Form-associated `submit` / `reset` support | Depends on the ElementInternals/tooling recommendation and is intentionally out of the initial Button scope. | [Must ship — breaking or a11y-required](#must-ship--breaking-or-a11y-required), [Deferred semantics note (2nd-gen)](#deferred-semantics-note-2nd-gen) |
+| SWC-2035 | Host `focus` / `blur` compatibility parity | Initial 2nd-gen Button will support `click` plus bubbling `focusin` / `focusout`; extra compatibility events can be evaluated later. | [Internal semantic button implications](#internal-semantic-button-implications), [Documentation](#documentation) |
+| SWC-2036 | React Spectrum-only `genai` and `premium` variants | Not part of the approved baseline Button scope in this migration plan. | [Additive](#additive--ships-when-ready-zero-breakage-for-consumers-already-on-2nd-gen), [Public API](#public-api) |
+
+---
+
+## References
+
+- [Washing machine workflow](../../02_workstreams/02_2nd-gen-component-migration/02_step-by-step/01_washing-machine-workflow.md)
+- [Accessibility migration analysis](./accessibility-migration-analysis.md)
+- [Rendering and styling migration analysis](./rendering-and-styling-migration-analysis.md)
+- [PR #6177 — Button accessibility migration analysis](https://github.com/adobe/spectrum-web-components/pull/6177)
+- [PR #6120 — core/shared migration and LikeAnchor removal](https://github.com/adobe/spectrum-web-components/pull/6120)
+- [CSS style guide — Component Custom Property Exposure](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/02_custom-properties.md#component-custom-property-exposure)
+- [CSS style guide — Selector conventions](../../../../CONTRIBUTOR-DOCS/02_style-guide/01_css/02_custom-properties.md#selector-conventions)
+- [1st-gen source](../../../../1st-gen/packages/button/src/Button.ts)
+- [1st-gen button base](../../../../1st-gen/packages/button/src/ButtonBase.ts)
+- [1st-gen tests](../../../../1st-gen/packages/button/test/button.test.ts)
+- [1st-gen README](../../../../1st-gen/packages/button/README.md)
+- [2nd-gen global button stylesheet](../../../../2nd-gen/packages/swc/stylesheets/global/global-button.css)
+- [2nd-gen global elements stylesheet](../../../../2nd-gen/packages/swc/stylesheets/global/global-elements.css)
+- [React Spectrum S2 Button](https://react-spectrum.adobe.com/Button)
+- [Global element styling guide](../../../../2nd-gen/packages/swc/.storybook/guides/customization/global-elements.mdx)
+- [Badge migration reference](../../02_workstreams/02_2nd-gen-component-migration/02_step-by-step/01_washing-machine-workflow.md#reference-badge-migration)
+- SWC-48: ElementInternals RFC
+- SWC-1139: ensure contrast ratio for static white, outline on :hover
+- SWC-459: pending state a11y criteria
+- SWC-701: issue with label and visibility: hidden
+- SWC-886: focus ring visibility vs. overflow: hidden
+- SWC-1873: Button Epic
+- SWC-2033: [Button] cross-root ARIA
+- SWC-2034: [Button] define support for form-associated submit / reset
+- SWC-2035: [Button] Host focus/blur compatibility
+- SWC-2036: [Button] add `genai` and `premium` variants