STV_ADR_006: Centered layout and interactive overview

Status: accepted. Date: 2026-10-18. Scope: software architecture. Decision owner: project owner through delegated concept review; see Concept review round 6: accepted centered-layout and seed-selection amendment. Supersedes: partially STV_ADR_005: Optional seed sets and paged project entry for page size, initial root expansion and runtime seed mutability. Superseded by: partially STV_ADR_008: Stable navigation after fresh placement for repeated parent recentering during group/root navigation; all other decisions remain.

Related requirements: Initially collapse traced o... (STV_SHR_003), Start from the project when... (STV_SHR_047), Center parents over their v... (STV_SHR_052), Select a starting object in... (STV_SHR_053), Initialize collapsed state (STV_SWR_003), Provide the artificial proj... (STV_SWR_051), Page stakeholder entry links (STV_SWR_052), Center parent boxes with co... (STV_SWR_056), Confirm local interactive s... (STV_SWR_057). Affected elements: Semantic rank layout (STV_SWE_LAYOUT), Exploration state engine (STV_SWE_STATE), Accessible view and viewport (STV_SWE_RENDER).

Context

The owner requested an inspectable MVP with centered parents, five-item overview pages and runtime seed selection. Existing graph data already carries all published IDs/titles; component boundaries and offline delivery suffice.

Decision

Initialize project mode with its first page of five entries open. Keep ordinary trace expansion collapsed and preserve independent page exploration on paging. Use a per-view local picker over the immutable published graph; a confirmed exact ID replaces that view’s seeds and exploration after capacity/layout validation. Project overview explicitly starts a fresh first-page overview. Keep author-supplied multi-seed syntax and source validation unchanged.

After ELK ordering and semantic projection, move parent boxes toward the midpoint of visible lower-level child spans. Resolve same-band collisions deterministically before recomputing test lanes and final routes. Interpret parent/child by semantic rank, independent of edge authorship. Ignore same-rank and test-role connections for centering; keep shared children single nodes.

Rationale

Five entries provide immediate useful content and leave capacity for exploration. Local search reuses authoritative published data without a new backend or rebuild. Transactional replacement preserves the committed view on errors. Collision constraints preserve readability where exact centering is impossible.

Consequences and constraints

Selection discards only its view’s prior exploration; it does not edit Needs, RST defaults or another instance. Search suggestions may be bounded with total match information; direct exact-ID entry remains possible. This decision replaces ADR 005’s page size, initial root expansion and runtime seed immutability choices; its unaffected decisions remain applicable.

Alternatives considered

Viewport-centered parents ignore child geometry. Duplicating shared children breaks shared identity. Adding a selected seed preserves unrelated exploration against the confirmed replacement intent. Rebuilding RST for every selection does not provide the requested reader workflow. None is selected.

Verification and handover

Use focused geometry/state and Firefox file/HTTP cases from Implementation verification plan. Concept acceptance is recorded in Concept review round 6: accepted centered-layout and seed-selection amendment. Full release qualification remains separate; see Centered parents and interactive seed selection.