Components: Generate MenuButton

Summary

Generate MenuButton with its canonical contract, implementation, tests, stories, platform validation, and explicit package export so buttons can expose related action menus. MenuItem is available, but the component remains downstream of the shared Popover and Menu implementations.

Observed. menu-button is entry menu-button in the canonical catalog and has no
implementation in packages/agentic/components. Upstream describes it as: Button that opens a Menu of action options. Composes a Button-styled trigger with an always-present trailing chevron and boolean label and leading-icon slots, plus a Menu overlay. Forwards Button's Style, Size, and State axes, collapses Button's Layout axis into the two slot booleans, and exposes Open coupled to State=Pressed. Triggers actions, not selections.

Goal

Generate the menu-button component in
packages/agentic/components/src/components against the
canonical Fluent Flex spec, with the colocated coverage, stories, and platform
validation the package requires, and export it explicitly from
src/index.ts.

Stage

Stage 3 (production). Wave 3 - focus-orchestrated and composed.

Why it matters

Observed. The canonical catalog has 50 components and the agentic library has
generated 18. menu-button is one of the 32 in the gap, enumerated in
the missing-components index.

Inferred. It is a composed or focus-orchestrated component whose blockers resolve once the wave 2 overlay stack and the focus decision land, so it is a direct measure of whether those foundations were built correctly.

Observed current state

Canonical spec and source

Field	Value
Canonical spec	plugins/components/skills/menu-button/SKILL.md with usage.md, web/tokens.yaml, web/accessibility.md, and web/interaction.md, at x3-design/fluent-design @ d334acf
Upstream tier	molecule
Upstream catalog key	menu-button in component-map.yaml
Local staged spec	packages/agentic/components/specs/menu-button - SPEC.md, usage.md, interaction.md, accessibility.md, tokens.yaml, blockers.md
Local implementation	None. No src/components/menu-button directory exists

Closest existing FURN or V1 implementation

• packages/components/MenuButton - MenuButton.tsx is the cross-platform desktop path; MenuButton.macos.tsx with MacOSMenuButtonNativeComponent.ts is a macOS-specific native implementation.
• packages/experimental/MenuButton - MenuButton.tsx, MenuButton.styling.tsx, and renderContextualMenu.tsx - a ContextualMenu-based variant with no platform-specific files.

Note on platform canon. Where a legacy package has platform-specific files, the
desktop path (.win32, .windows, .macos, or the unsuffixed cross-platform file)
is the compatibility reference. .ios, .android, and .mobile variants are not
treated as the cross-platform canonical implementation.

Local dependencies

• src/components/button - Observed present (component).
• src/components/menu-item - Observed present (component).
• src/primitives/icon - Observed present (primitive).

Known blockers

Observed (blockers.md, blocker class B in the index).

Three blockers were recorded: the spec depends on Menu, Popover, and MenuItem while "this package currently only implements Button and Icon"; the manifest exposes no local dependency path to the menu and popover stack; and the session could not create the missing supporting components.

Reassessment.

Partly stale. menu-item now exists. Menu and Popover do not. Inferred: unblocked by popover and menu.

Scope

• Ingest or promote the spec into the component directory in the generated shape
  (SPEC.md plus a spec/ folder), per
  spec-ingestion-and-generation.md.
• Establish the public contract first: variants, slots, native props, accessibility,
  interaction states, and platform behavior.
• Implement the required file structure from
  src/components/AGENTS.md:
  menu-button.types.ts, menu-button.styles.ts, use*.ts, use*Styles.ts, render*.tsx, and
  the assembly module with a displayName.
• Style from Flex tokens first and record genuine token gaps rather than substituting
  unrelated values.
• Export the component, its public types, and the state, style, and render stages
  explicitly from src/index.ts under component-qualified unstable names.
• Compose menu for the overlay rather than re-implementing it.
• Honor the upstream distinction: MenuButton triggers actions; selection belongs to dropdown.
• Implement the collapsed layout axis as two boolean slots on one chrome set, which differs from the local button's single icon slot plus iconPosition.

Out of scope

• Changing the contract of an existing generated component, unless this task explicitly
  calls for it above; raise it as its own item.
• Building shared infrastructure owned by another task: overlay hosting
  (popover), roving focus (focus-zone.md), spec
  ingestion (spec-ingestion-and-generation.md),
  or the coverage contract (component-test-strategy.md).
• Migrating any legacy FURN consumer onto this component.
• Mobile platform support; the applicable upstream companion is web, retargeted to
  React Native for Windows and macOS.

Deliverables

• src/components/menu-button/ implementing the full required file structure.
• SPEC.md and a spec/ companion folder with provenance recording the upstream path,
  SHA, and ingestion date.
• Colocated menu-button.test.tsx, menu-button.types.test.ts, and menu-button.stories.tsx.
• Snapshot coverage where the visual contract is state-dependent, or a recorded
  exemption.
• Explicit exports from src/index.ts, with src/index.test.ts updated.
• A changeset, per the repository's version management rules.
• A recorded readiness level with its supporting evidence.

Required coverage, stories, and platform validation

Runtime and type coverage:

• Every forwarded Button style, size, and state.
• Both slot booleans in all four combinations, with the chevron always present.
• Open couples to the pressed visual state.
• Trigger reports its expanded state and its menu relationship in the accessibility tree.
• Menu dismissal returns focus to the trigger.
• User style and handler forwarding, and that user styles are applied after component
  styles.
• Compile-time slot acceptance and any mutually exclusive props.

Stories: a typed Meta titled Components/MenuButton, an args-driven Default, a
grouped Overview when the contract has several axes, one focused story per variant
axis, and an interactive story for each stateful axis. Self-driving axes expose
default<State> as the control; externally driven selection is owned by the story with
React.useState. Identity-changing axes are not exposed as controls.

Platform validation: the component's stories render and behave correctly on macOS
and on React Native Windows Fabric through apps/storybook,
including hover, pressed, disabled, focus, optional-slot, and constrained-content
scenarios. Add a stable root testID if the component joins the automated smoke set.

Acceptance criteria

• src/components/menu-button exists with the required file structure and a displayName.
• Every variant axis in the component's SPEC.md is implemented, or a deviation is recorded in the spec.
• The component styles from Flex tokens, with any genuine token gap recorded rather than approximated.
• Focus feedback renders through FocusVisual; no outline* props and no React Native Windows native focus visuals are introduced.
• State precedence is explicit: disabled wins over pressed, which wins over hovered.
• Every stateful axis is classified as self-driving or externally driven, and both paths are covered.
• Runtime, type, and story coverage satisfy the package coverage contract.
• The component, its public types, and its pipeline stages are exported explicitly from src/index.ts, and src/index.test.ts covers them.
• The component's stories render on macOS and on React Native Windows Fabric.
• yarn workspace @fluentui-react-native/components format, lint, build, and test pass, and the Storybook bundle succeeds for both desktop platforms.
• A readiness level is recorded with its supporting evidence.
• A changeset is included.

Dependencies and ordering

• Blocked by wave 2, either directly or through a wave 2 dependency listed above.
• Gated by component-test-strategy.md: the component must satisfy the coverage contract on arrival rather than being retrofitted.
• Gated by readiness-model.md: the target readiness level must be stated before the work starts.
• Consumes the Infrastructure workstream (storybook-e2e.md) for automated macOS and Windows Fabric validation; until it lands, platform validation is manual.

Risks and open decisions

1. The slot-boolean contract conflicts with the local button icon model, which is itself drifted from upstream; resolving button first would avoid a third icon convention.
2. FURN already has two legacy MenuButton implementations with different architectures, so migration guidance will be needed.

Evidence and references

• Upstream spec: plugins/components/skills/menu-button/SKILL.md and
  components-index/SKILL.md
  at x3-design/fluent-design @ d334acf.
• Local staged spec and blocker record: packages/agentic/components/specs/menu-button.
• Canonical implementations to follow: src/components/button
  for a styled higher-order component and src/primitives/icon
  for a primitive.
• Authoring rules: src/components/AGENTS.md and the
  agentic component authoring skill.
• Workstream context: Components README and
  the missing-components index.

Sources retrieved 2026-08-20.

Start with packages/agentic/components/specs/menu-button and src/components/AGENTS.md, then compare the existing button and menu-item implementations. Check issues 4232 and 4236 before beginning, since Menu and Popover are stated blockers. Done requires the required component files, colocated tests and stories, platform validation, explicit index exports, spec provenance, and a changeset.