Pure traversal that walks a node's declared `relations` and returns the
full set of IDs that should be marked dirty alongside it. Two
implementations:
- `cascadeDirty(id, ctx)` — follows `hosts` (matching children) and
`affectsSpatial` (via injected spatialQuery). Phase 3 will add
`linkedBy: 'endpoint-match'`.
- `collectDescendants(id, ctx)` — pure subtree traversal for
`cascadeDelete: 'descendants'` and subtree deletion tools.
Both bounded by maxDepth (default 16) and visited-set so cycles in
bad data can't loop forever.
Context-based design: spatialQuery and childQuery are injected, so the
resolver itself stays pure — the DragAction runtime can plug in
spatialGridManager-backed queries; tests pass stubs.
Today, registry has no kinds → cascadeDirty(id) always returns just
{id}. No behavior change. Phase 3 wall is the first real consumer.
11 unit tests cover empty/no-relations baseline, hosts cascade, depth
limit, spatial query, missing spatialQuery branch, cycle protection,
childQuery override, descendant collection.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
