Components: Generate Breadcrumb

Summary

Generate Breadcrumb with its canonical contract, implementation, tests, stories, platform validation, and explicit package export so hierarchical navigation is available in the agentic library. Delivery remains blocked on the shared Popover, Menu, and Tooltip stack required for overflow behavior.

Observed. breadcrumb is entry breadcrumb in the canonical catalog and has no
implementation in packages/agentic/components. Upstream describes it as: Navigation trail showing a user's hierarchical location. Covers an interactive BreadcrumbItem extending Button Subtle, a non-interactive CurrentItem, a Separator, Overflow (Visible/Collapsed with Popover), Tooltip for the overflow count and truncated labels, and Small/Medium/Large sizes.

Goal

Generate the breadcrumb 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. breadcrumb 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/breadcrumb/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	breadcrumb in component-map.yaml
Local staged spec	packages/agentic/components/specs/breadcrumb - SPEC.md, usage.md, interaction.md, accessibility.md, tokens.yaml, blockers.md
Local implementation	None. No src/components/breadcrumb directory exists

Closest existing FURN or V1 implementation

• No breadcrumb exists in any FURN catalog. The closest structural precedent is packages/experimental/Overflow, which implements an overflow manager, a priority queue, and an overflow menu for a horizontal item strip.

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/primitives/icon - Observed present (primitive).

Known blockers

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

Three blockers were recorded: the spec depends on Popover, Menu, and Tooltip behaviors; "this package currently only contains Button and Icon" with no breadcrumb source tree and no in-package overflow or tooltip surfaces; and the manifest provides no dependency path to the experimental popover and tooltip packages.

Reassessment.

Valid in substance, stale in detail. The package is no longer Button and Icon only, but Popover, Menu, and Tooltip are all still missing. Inferred: unblocked once wave 2 delivers popover, menu, and tooltip.

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:
  breadcrumb.types.ts, breadcrumb.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.
• Decide whether overflow collapsing is measured at runtime or driven by a caller-supplied maximum; the Overflow package is prior art for the measured approach.
• Sub-parts (BreadcrumbItem, CurrentItem, Separator) are owned by this task and do not get separate tasks, per the inclusion rules in the index.

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

• All three sizes.
• Overflow Visible and Collapsed, including the collapsed popover contents.
• The current item is non-interactive and is marked as current in the accessibility tree.
• Tooltips on the overflow count and on truncated labels.
• Navigation role and the ordered relationship between items.
• Constrained-width behavior that forces collapsing.
• 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/Breadcrumb, 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/breadcrumb 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. Runtime measurement for overflow is asynchronous in React Native and can flicker on first layout.
2. It depends on three wave 2 components, so it is among the last components that can start.

Evidence and references

• Upstream spec: plugins/components/skills/breadcrumb/SKILL.md and
  components-index/SKILL.md
  at x3-design/fluent-design @ d334acf.
• Local staged spec and blocker record: packages/agentic/components/specs/breadcrumb.
• 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/breadcrumb/SPEC.md and its spec files, then read src/components/AGENTS.md and inspect the button and experimental Overflow implementations. Confirm the Popover, Menu, and Tooltip blockers before starting. Done means the breadcrumb source tree, colocated tests and stories, explicit exports, platform validation, changeset, and readiness evidence satisfy the listed acceptance criteria.