refactor: Unify section/group into single collapsible Group

[alex-fedotyev]

Summary

Merges the separate "section" and "group" container types into a single Group concept that is:

• Always bordered — clear visual container
• Always collapsible — chevron toggle with URL-based collapse state
• Optionally tabbed — add tabs to any group, tab bar appears with 2+ tabs

This addresses the UX concern from #1972 that "section" and "group" are near-synonyms that force users to choose between two similar concepts.

What changed

• Schema: Accepts 'section' for backward compatibility, new code always writes 'group'
• GroupContainer: Gains collapse chevron, tile count badge when collapsed, "Collapse by Default" toggle in overflow menu
• SectionHeader: Deleted — all functionality merged into GroupContainer
• Add menu: Single "New Group" item instead of "New Section" + "New Group"
• DnD components: Renamed from section to container terminology
• useDashboardContainers: handleAddContainer() always creates a group with 1 default tab
• useTileSelection: Cmd+G creates a group (not section)

Builds on

• feat: Dashboard sections, groups with tabs, and panel organization #1972 (dashboard sections, groups with tabs, and panel organization)

Test plan

• All 56 dashboard container tests pass
• All 1185 app unit tests pass
• ESLint clean
• Backward compatible — dashboards with type: 'section' containers still parse correctly
• No new TypeScript errors (pre-existing dnd-kit type issues unchanged)

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
hyperdx-oss	Ready	Preview, Comment	Mar 31, 2026 0:12am

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PR Review

Clean refactor that merges section/group into a unified Group container. Backward compatibility is handled correctly at the schema level (type: z.enum(['section', 'group'])). A few items to address:

• ⚠️ Accessibility regression in GroupContainer.tsx: The deleted SectionHeader had role="button", tabIndex={0}, aria-expanded, and onKeyDown (Enter/Space) on the collapse toggle. The new chevron and title Flex only use onClick — keyboard-only users can no longer toggle collapse. Add keyboard handler + ARIA to the collapse trigger.

• ⚠️ No unit tests for new GroupContainer collapse behavior: SectionHeader.test.tsx (152 lines) was deleted and GroupContainer gained significant new surface area (collapsed prop, onToggle, onToggleDefaultCollapsed, onRename), but no GroupContainer.test.tsx was added. The deleted tests covered toggle, tile count badge, and menu interactions — these behaviors are now untested.

• ℹ️ Tile count badge silently dropped: SectionHeader showed (N tiles) when collapsed; GroupContainer omits this. The latest commit message confirms it's intentional, but if it was a deliberate UX decision it should be noted in the PR description (it's currently missing from the "What Changed" section).

✅ Schema backward compat, hook renaming, DnD refactor, and the render-path unification all look correct.