fix(DateInput): hardening — swarm findings

[josephfarina]

Hardening fixes for XDSDateInput and dateParser.

Changes

DateInput component

• isEffectivelyDisabled: input disabled during isBusy (prevents interaction during async updates)
• Constraint validation on text input via isDateDisabled (previously only calendar enforced min/max)
• ARIA combobox role: role="combobox", aria-expanded, aria-haspopup="dialog", aria-controls
• Enter key commits typed date (same as blur behavior)
• ArrowDown opens calendar popover (APG combobox pattern)
• Fix pendingInput not cleared by self-triggered value changes (typing kept getting overwritten by formatted date)
• Calendar shows optimisticValue instead of stale value
• Clear pending input on external value change via useEffect
• ISO format regex guard on displayValue

dateParser

• Fix years 0-99 mapping to 1900s (date.setFullYear(year) after construction)
• Reject mixed separators (e.g. 1/25.2026 → null)
• 4-digit year padding in dateToISO

Tests

• 4 new tests: year 0-99 preservation, mixed separator rejection, Enter key commit, ArrowDown opens popover

Screenshots

Story	Screenshot
Default
With Value
Disabled
Min/Max
Two Month
Error Status
All Variations

[github-actions]

PR Analysis Report

📚 Storybook Preview

View Storybook for this PR
GitHub Pages may take up to a minute to hydrate after deploy.

🧪 Sandbox Preview

View Sandbox for this PR
GitHub Pages may take up to a minute to hydrate after deploy.

Modified Components

DateInput · View in Storybook

Metric	Before	After	Delta
Bundle Size (ESM)	N/A	848B	N/A
Lines of Code	N/A	413	-
Complexity	N/A	Very High (57)	-

Bundle Size Summary

Package	Size (ESM)	Size (CJS)	Gzipped
@xds/core	11.0KB	17.6KB	2.7KB

Accessibility Audit

Status: No accessibility violations detected.

---

_{Generated by PR Enrichment workflow | Storybook | Sandbox | View full report}

[cixzhang]

Hardening review:

Remove ArrowDown/Alt+ArrowDown keyboard shortcut to open calendar from input. The calendar already has an open mechanism (icon button), and this shortcut is incomplete without also moving focus into the calendar grid.

[josephfarina]

Removed the ArrowDown shortcut and its test per Cindy's review. Good call, it was incomplete without focus management into the calendar grid.