Why

The change > Specs tab currently shows side-by-side full specs plus a unified line diff — three views of the same data with no summary of what actually changed at the requirement level. For a change that touches one scenario in a 10-requirement spec, the maintainer has to scan two full documents to find the difference. The semantic delta computed by the shared parser (from the semantic-spec-diff-tool change) should drive this view instead.

What Changes

Replace the "Diff vs current" side-by-side view in ChangeSpecsView with a semantic delta view. The backend _change_detail function computes a semantic_diff field per spec. The frontend renders a summary-first view: requirement-level added/modified/removed sections with scenario-level deltas inside modified requirements, unchanged requirements collapsed by default, and the unified line diff as a collapsible raw fallback at the bottom.

Capabilities

New Capabilities

• change-specs-semantic-diff-view: Frontend SpecDeltaView component and backend semantic_diff field in change detail, rendering requirement-level deltas instead of side-by-side full specs

Modified Capabilities

• change-board: The "Delta spec comparison" requirement is modified to include semantic diff alongside the existing unified diff in change detail responses

Impact

• dashboard/plugin_api.py — _change_detail computes semantic_diff per spec using the shared _semantic_spec_diff function
• dashboard/dist/index.js — new SpecDeltaView component; ChangeSpecsView updated to use it for the diff mode
• dashboard/dist/style.css — styles for delta sections, added/modified/removed badges, collapsible unchanged requirements
• openspec/specs/change-board/spec.md — delta spec modifying the "Delta spec comparison" requirement

Dependencies

• Requires semantic-spec-diff-tool — the shared _parse_spec and _semantic_spec_diff functions must exist in tools.py before the backend can use them