Make Code Graph open from a prepared overview

[forhappy]

What changed

• generate an atomic graph-overview.json presentation artifact during clustered updates and cluster-only
• load and validate the prepared overview directly in the VS Code extension
• cache the one-time CLI fallback in extension storage for repositories built by older Compass versions
• keep immutable full-graph snapshots and lazy community details in the background
• show a design-token-native “Preparing a large code graph” state with graph size and phase for cold graphs over 8 MB

Why

Opening Code Graph reparsed and aggregated the complete graph.json through a new CLI process every time. On a 22 MB real repository graph, that path took 1.33 seconds before the webview could hydrate. The prepared 325 KB overview parses in 0.02 seconds, about 66× faster.

Compatibility

Existing repositories continue to work. When graph-overview.json is missing, stale, malformed, or uses a different configured node limit, Compass falls back to the existing CLI export and caches that result in VS Code storage. The full graph remains authoritative for lazy community exploration.

Validation

• cargo fmt --all --check
• cargo test -p compass-core -p compass-output
• npm test -w compass-vscode
• npm run typecheck -w compass-vscode
• npm run typecheck -w @compass/viewer
• npm run build -w compass-vscode
• npm test -w @compass/viewer-tests -- loading.spec.ts performance.spec.ts
• git diff --check
• graphify update .