fix: nested entity persistence, subscription propagation and temp ID rekey

[vparys]

Summary

Fixes a set of related bugs where creating nested entities (e.g. Program → Approval → Round → Review) via inline creates, persisting them, and then modifying them would either generate incorrect mutations or fail to update the UI.

The changes span three areas: mutation generation for deeply nested entities, temp-to-persisted ID remapping after persist, and subscription/parent-child propagation so React components re-render correctly.

Changes

1. Nested hasMany mutation generation

Problem: MutationCollector used processNestedData for hasMany items nested inside a parent create, which only looked at raw embedded data in the entity snapshot. Items added via store.addToHasMany (tracked in RelationStore) were ignored — the generated mutation was missing nested entities.

• MutationCollector now uses collectCreateData for nested hasMany entities, which properly checks both embedded data and store-managed hasMany state.
• Embedded relation data (e.g. reviews: [{ reviewType: 'expert' }]) is materialized into tracked store entities with temp IDs during mutation building via materializeEmbeddedHasMany/materializeEmbeddedHasOne, enabling proper post-persist ID mapping and commit.

2. Nested entity ID mapping from persist responses

Problem: After persistAll(), inline-created nested entities got server-assigned UUIDs, but the store had no way to map the temp IDs to persisted IDs. Subsequent modifications would generate mutations with temp IDs that the server didn't recognize.

• BatchPersister.commitNestedResults processes nestedResults from the adapter response, committing nested entities and calling mapTempIdToPersistedId for each.
• ContemberAdapter extracts nested entity IDs from GraphQL mutation response node data.
• Sequential persist fallback path also extracts nested IDs from response data.

3. Subscription and parent-child migration on temp→persisted ID rekey

Problem: After mapTempIdToPersistedId, entity data moved from key EntityType:__temp_xxx to EntityType:real-uuid, but React components (via useSyncExternalStore) were still subscribed to the old key. Notifications on the new key reached nobody — UI appeared frozen until page refresh.

• SnapshotStore adds rekeyedEntities map so getEntityKey/getRelationKey transparently resolve temp IDs to persisted keys for all store operations (subscribe, read, write).
• mapTempIdToPersistedId now atomically rekeys entity snapshots, metadata, relations, errors, touched state, and subscriptions.
• SubscriptionManager adds rekeyedKeys map so unsubscribe closures (which capture the original key at subscribe time) correctly find and remove migrated callbacks. Without this, useSyncExternalStore's unsub/resub cycle would leak the old callback.
• SubscriptionManager.rekey() migrates entity subscribers, relation subscribers (by prefix), and childToParents entries (both as child and parent references), preserving the full propagation chain across arbitrary nesting depths.
• Sub-store rekey() methods added to EntityMetaStore, EntitySnapshotStore, ErrorStore, RelationStore, TouchedStore.

4. $create() method on HasOne handle

Problem: Creating and connecting a new entity to a hasOne relation required the low-level store.createEntity() + $connect() pattern.

• HasOneHandle.$create(data?) creates a new entity of the target type and connects it in one call, returning the temp ID. Consistent with HasManyListHandle.add().

5. Parent-child registration in ActionDispatcher

Problem: registerParentChild (which sets up subscription propagation from child to parent) was only called from high-level handle methods. Dispatching actions directly or using the low-level store API would not set up the propagation chain.

• ActionDispatcher.execute now calls registerParentChild for ADD_TO_LIST, CONNECT_TO_LIST, and CONNECT_RELATION actions.
• Added targetType field to ConnectRelationAction and ConnectToListAction interfaces.
• Removed redundant registerParentChild calls from HasManyListHandle.add(), HasManyListHandle.connect(), and HasOneHandle.$create().

Test plan

• bun test — 1412 pass, 9 pre-existing failures (8 browser tests needing running server, 1 unrelated formRelations test)
• bun run typecheck — clean
• 25+ new tests across nestedHasManyCreate.test.ts, subscriptionRekey.test.ts, actionDispatcher.test.ts, hasOneHandle.test.ts
• Manual verification: create nested entities via UI → persist → modify → persist again → UI updates without page refresh