Components: Generate Dropdown

[JasonVMo]

Summary

Generate Dropdown with its canonical contract, implementation, tests, stories, platform validation, and explicit package export so select-only choice workflows are covered. Input and option-row dependencies now exist, but the Popover surface and virtual-focus behavior remain blocking.

Observed. dropdown is entry dropdown in the canonical catalog and has no
implementation in packages/agentic/components. Upstream describes it as: Composed selection control pairing an Input-styled non-editable button trigger with an overlay Popover containing selectable rows. Composes Input trigger chrome, Popover surface and light-dismiss behavior, and ListboxItem rows; forwards Input's Style and Size axes and exposes Selection mode (Single/Multiple) and Open. Uses select-only combobox semantics with trigger-owned virtual focus.

Goal

Generate the dropdown 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 2 (beta). Wave 2 - overlay and popover stack.

Why it matters

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

Inferred. It belongs to the overlay stack, which is the largest single cluster of blocked components. Delivering the cluster converts a broad "not implementable" state into ordinary component work.

Observed current state

Canonical spec and source

Field	Value
Canonical spec	plugins/components/skills/dropdown/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	dropdown in component-map.yaml
Local staged spec	packages/agentic/components/specs/dropdown - SPEC.md, usage.md, interaction.md, accessibility.md, tokens.yaml, blockers.md
Local implementation	None. No src/components/dropdown directory exists

Closest existing FURN or V1 implementation

• packages/experimental/Dropdown - Dropdown/, Listbox/, and Option/ subtrees - the closest legacy equivalent, with no platform-specific files, so it is the cross-platform and desktop reference.

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/input - Observed present (component).
• src/components/listbox-item - Observed present (component).

Known blockers

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

Three blockers were recorded: the spec is a composition of trigger chrome, a Popover surface, and ListboxItem rows and "this package currently has only Button and Icon source"; the session could not add or connect the missing dependencies; and the authored focus movement, open/close management, and row selection semantics all depend on those missing pieces.

Reassessment.

Partly stale. src/components/listbox-item and src/components/input now exist. Only the Popover surface and the virtual-focus model remain. Inferred: unblocked by popover.

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:
  dropdown.types.ts, dropdown.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.
• Reuse the input chrome for the trigger rather than restyling a button, matching the upstream delegation statement.
• Implement the virtual-focus model: the trigger keeps real focus while an active row is tracked, which is different from moving focus into the list.
• Support both Single and Multiple selection modes with the correct row indicators.

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/dropdown/ implementing the full required file structure.
• SPEC.md and a spec/ companion folder with provenance recording the upstream path,
  SHA, and ingestion date.
• Colocated dropdown.test.tsx, dropdown.types.test.ts, and dropdown.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:

• Both selection modes, and both Input styles across all three sizes.
• Open and closed, controlled and uncontrolled.
• Keyboard: open, move the active row, commit, and dismiss.
• Trigger role, expanded state, and the active-row relationship in the accessibility tree.
• Selecting a row updates the value and, in Single mode, closes the surface.
• 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/Dropdown, 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/dropdown 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 popover for the overlay host, anchoring, light dismiss, and focus return.
• 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. Virtual focus has no React Native precedent in this repository; asserting it requires accessibility-tree checks rather than focus assertions.
2. dropdown, combobox, and select are three upstream entries over similar ground; settle their shared internals before building the second one.

Evidence and references

• Upstream spec: plugins/components/skills/dropdown/SKILL.md and
  components-index/SKILL.md
  at x3-design/fluent-design @ d334acf.
• Local staged spec and blocker record: packages/agentic/components/specs/dropdown.
• 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.