Tab layout for plan entity pages

TOC and section-nav coordination

The desktop TOC sidebar and mobile section-nav dropdown must remain generic — they know nothing about tabs. A plan-specific coordinator behavior bridges the two systems:

• Listens for anchor navigation (click or hashchange) where the target #id is inside an inactive tab panel
• Activates the correct panel before the browser scrolls to the anchor
• On desktop, the TOC sidebar can be visually dimmed or collapsed when a non-Overview tab is active (CSS-only, no TOC code changes)
• The section-nav dropdown entries for Relationships and History activate their respective tabs

This coordinator lives in the plan package's behaviors map alongside the existing milestone-backlog entry. The TOC scrollspy behavior and section-nav behavior remain untouched.

Acceptance Criteria

• postProcess wraps entity content in a tab-group structure with Overview, Relationships, and History panels
• Tab structure uses the same HTML contract as tabsBehavior (tablist buttons + tabpanel divs)
• tabsBehavior is registered for plan entity tab groups in the plan package behaviors map
• Tabs are omitted when the entity has no relationships and no meaningful history (single commit)
• Overview panel contains the existing rune body content unchanged
• Relationships panel contains the buildRelationshipsSection output (currently appended inline)
• History panel contains the buildAutoHistorySection output (currently appended inline)
• Plan-specific coordinator behavior activates the correct tab when navigating to an anchor inside an inactive panel
• Desktop TOC sidebar dims or hides via CSS when a non-Overview tab is active (no changes to TOC component code)
• Mobile section-nav dropdown entries for Relationships/History activate their respective tabs
• CSS for tab bar styled consistently with existing plan page chrome
• Existing plan pages without relationships or history render identically to before (no regressions)

Dependencies

• plan-history site rune — tag definition and pipeline hooks — Plan history rune implementation (provides the history data)

Approach

Pipeline changes (runes/plan/src/pipeline.ts)

In postProcess, instead of appending relationship and history sections as children of the rune tag, wrap them in a tab-group structure:

1. Extract the existing rune body children as the Overview panel content
2. Build Relationships panel from buildRelationshipsSection (already implemented)
3. Build History panel from buildAutoHistorySection (already implemented)
4. If neither panel has content, return the rune unchanged (no tab wrapper)
5. Emit a wrapper element with data-rune="plan-entity-tabs" containing:
   • [data-name="tabs"] div with role="tablist" and three buttons
   • [data-name="panels"] div with three role="tabpanel" divs

Behavior registration (runes/plan/src/index.ts)

Add 'plan-entity-tabs': tabsBehavior to the plan package's behaviors map so the tab interaction is wired up automatically.

Coordinator behavior (runes/plan/src/behaviors/tab-nav-coordinator.ts)

A small behavior registered for plan-entity-tabs elements that:

• Intercepts anchor clicks where the target heading lives inside a tab panel
• Activates the panel containing the target before scroll
• Listens for hashchange for the same purpose (back/forward navigation)

CSS (runes/plan/styles/)

• Tab bar styling consistent with existing plan chrome (badge colors, font sizes)
• Active tab indicator using plan design tokens
• [data-state="inactive"] on panels hides content (standard tabs pattern)
• .rf-plan-toc gets opacity/pointer-events reduction when a [data-active-tab] attribute is not "overview" (CSS-only, scoped to plan layout)

Config (runes/plan/src/config.ts)

Add a PlanEntityTabs rune config entry with block: 'plan-entity-tabs' for BEM class generation.

References

• runes/plan/src/pipeline.ts — postProcess hook (lines 640-664) where relationship/history injection currently happens
• packages/behaviors/src/behaviors/tabs.ts — tabsBehavior HTML contract
• packages/behaviors/src/behaviors/scrollspy.ts — TOC scrollspy (must not be modified)
• packages/behaviors/src/behaviors/section-nav.ts — mobile section nav (must not be modified)
• runes/plan/src/config.ts — plan rune configs

Resolution

Completed: 2026-04-13

Branch: claude/work-item-tab-layout-dm34n

What was done

• runes/plan/src/pipeline.ts — Modified postProcess to partition entity children into structural (header, meta fields) and body content, wrapping the body in a tab-group with Overview/Relationships/History panels via new buildEntityTabGroup function. Tabs only emitted when at least one metadata panel has content.
• runes/plan/src/entity-tabs-behavior.ts — New composite behavior wrapping tabsBehavior with: anchor navigation coordination (intercepts TOC/section-nav clicks and hashchange to activate the correct panel before scrolling), MutationObserver tracking aria-selected to expose data-active-tab attribute for CSS.
• runes/plan/src/config.ts — Added PlanEntityTabs rune config (block: 'plan-entity-tabs') for BEM class generation.
• runes/plan/src/index.ts — Registered entityTabsBehavior for plan-entity-tabs in the package's behaviors map.
• runes/plan/src/commands/plan-behaviors.ts — Registered entityTabsBehavior for client-side behavior initialization.
• packages/lumina/styles/runes/plan-entity-tabs.css — Tab bar and panel styling (underline indicator, active state, consistent with core tabs rune), TOC dimming via :has([data-active-tab]) when a non-Overview tab is active.
• packages/lumina/index.css — Added CSS import for new file.
• runes/plan/tsconfig.json — Added DOM lib for client-side behavior types.
• contracts/structures.json — Regenerated with new rune config (117 runes).

Notes

• The tabs rune itself cannot be used because relationship/history data is synthesized during postProcess (after schema transform). Instead, the pipeline emits the same HTML contract that tabsBehavior expects.
• TOC and section-nav behaviors remain completely untouched — the coordinator behavior bridges them via document-level click/hashchange listeners scoped to the tab panels container.
• All 2094 tests pass with no regressions.