feat: migrate objectMetadata reads to granular metadata store (#18643)

## Summary

Consolidates `objectMetadataItems` onto the metadata store as the
**single source of truth**, replacing the previous dual-store approach
(separate `objectMetadataItemsState` atom + untyped
`metadataStoreState`).

### Architecture: three-layer design

```
┌─────────────────────────────────────────────────────────┐
│ Store Layer (granular, typed)                           │
│  objectMetadataItems → FlatObjectMetadataItem[]         │
│  fieldMetadataItems  → FlatFieldMetadataItem[]          │
│  indexMetadataItems  → FlatIndexMetadataItem[]           │
└────────────────┬────────────────────────────────────────┘
                 │ .current (never draft)
┌────────────────▼────────────────────────────────────────┐
│ Selectors (typed read-only)                             │
│  objectMetadataItemsSelector                            │
│  fieldMetadataItemsSelector                             │
│  indexMetadataItemsSelector                             │
│  metadataStoreStatusFamilySelector                      │
│  isSystemObjectByNameSingularFamilySelector (narrow)    │
│  activeObjectNameSingularsSelector (narrow)             │
└────────────────┬────────────────────────────────────────┘
                 │ joins objects + fields + indexes + permissions
┌────────────────▼────────────────────────────────────────┐
│ Joining Selector                                        │
│  objectMetadataItemsWithFieldsSelector                  │
│  → produces full ObjectMetadataItem[] with              │
│    readableFields / updatableFields from permissions    │
│  → 12 existing selectors repointed here                 │
└─────────────────────────────────────────────────────────┘
```

### Key changes

- **Granular flat types** (`FlatObjectMetadataItem`,
`FlatFieldMetadataItem`, `FlatIndexMetadataItem`) — objects stored
without embedded fields/indexes, matching backend "Flat" naming
convention
- **Typed write API** — `updateDraft` is now generic via
`MetadataEntityTypeMap`, giving compile-time safety on what data shape
goes to each key
- **Write path refactored** — fetch → split into flat entities via
`splitObjectMetadataItemWithRelated` → write to metadata store directly.
No more dual-write through `objectMetadataItemsState`. Permissions
enrichment moved from write path into the joining selector.
- **SSE effects write directly** — `ObjectMetadataItemSSEEffect` and
`FieldMetadataSSEEffect` now patch the store from the SSE event payload
(create/update/delete) instead of triggering a full re-fetch
- **`objectMetadataItemsState` bridge** — converted from writable
`createAtomState` to read-only `createAtomSelector` that delegates to
the joining selector. All 100+ existing consumers continue to work
without code changes.
- **All selectors use Twenty state API** — `createAtomSelector` /
`createAtomFamilySelector` throughout, no raw `atom()`
- **Narrow selectors** for hot paths —
`isSystemObjectByNameSingularFamilySelector` and
`activeObjectNameSingularsSelector` read from flat objects only,
avoiding re-renders when fields/indexes/permissions change. Placed in
`object-metadata/states/` as higher-level business selectors.
- **Test helper** — `setTestObjectMetadataItemsInMetadataStore` for
tests that need to set up composite object metadata through the store
(clearly named as a testing utility)

### Naming conventions

- `ObjectMetadataItemWithRelated` — type for objects with embedded
fields/indexes (input to split utility)
- `FlatObjectMetadataItem` / `FlatFieldMetadataItem` /
`FlatIndexMetadataItem` — granular store types
- Selector names don't expose "Current" — that's an internal detail of
the metadata store API

### Future work

- Optimistic update API (`updateCurrentOptimistically` with rollback)
- Migrate remaining entities (views, pageLayouts, etc.) to the same
pattern
- Gradually remove `objectMetadataItemsState` bridge once all direct
imports are replaced

## Test plan

- [x] `npx nx typecheck twenty-front` passes
- [x] `npx nx lint:diff-with-main twenty-front` passes
- [ ] Verify app loads correctly with metadata from the store
- [ ] Verify SSE updates (object/field changes) propagate correctly
- [ ] Run existing test suites to confirm no regressions

packages/twenty-front/src/testing/jest/JestObjectMetadataItemSetter.tsx

@@ -1,8 +1,8 @@
 import { type ReactNode, useEffect, useState } from 'react';
 
-import { objectMetadataItemsState } from '@/object-metadata/states/objectMetadataItemsState';
+import { useMetadataStore } from '@/metadata-store/hooks/useMetadataStore';
+import { splitObjectMetadataItemWithRelated } from '@/metadata-store/utils/splitObjectMetadataItemWithRelated';
 import { type ObjectMetadataItem } from '@/object-metadata/types/ObjectMetadataItem';
-import { useSetAtomState } from '@/ui/utilities/state/jotai/hooks/useSetAtomState';
 import { generatedMockObjectMetadataItems } from '~/testing/utils/generatedMockObjectMetadataItems';
 
 export const JestObjectMetadataItemSetter = ({
@@ -12,15 +12,20 @@ export const JestObjectMetadataItemSetter = ({
   children: ReactNode;
   objectMetadataItems?: ObjectMetadataItem[];
 }) => {
-  const setObjectMetadataItems = useSetAtomState(objectMetadataItemsState);
+  const { updateDraft, applyChanges } = useMetadataStore();
   const [isLoaded, setIsLoaded] = useState(false);
 
   useEffect(() => {
-    setObjectMetadataItems(
-      objectMetadataItems ?? generatedMockObjectMetadataItems,
-    );
+    const items = objectMetadataItems ?? generatedMockObjectMetadataItems;
+    const { flatObjects, flatFields, flatIndexes } =
+      splitObjectMetadataItemWithRelated(items);
+
+    updateDraft('objectMetadataItems', flatObjects);
+    updateDraft('fieldMetadataItems', flatFields);
+    updateDraft('indexMetadataItems', flatIndexes);
+    applyChanges();
     setIsLoaded(true);
-  }, [objectMetadataItems, setObjectMetadataItems]);
+  }, [objectMetadataItems, updateDraft, applyChanges]);
 
   return isLoaded ? <>{children}</> : null;
 };

packages/twenty-front/src/testing/utils/setTestObjectMetadataItemsInMetadataStore.ts

@@ -0,0 +1,32 @@
+import { metadataStoreState } from '@/metadata-store/states/metadataStoreState';
+import { splitObjectMetadataItemWithRelated } from '@/metadata-store/utils/splitObjectMetadataItemWithRelated';
+import { type ObjectMetadataItem } from '@/object-metadata/types/ObjectMetadataItem';
+import { type createStore } from 'jotai';
+
+type JotaiStore = ReturnType<typeof createStore>;
+
+export const setTestObjectMetadataItemsInMetadataStore = (
+  store: JotaiStore,
+  objectMetadataItems: ObjectMetadataItem[],
+) => {
+  const { flatObjects, flatFields, flatIndexes } =
+    splitObjectMetadataItemWithRelated(objectMetadataItems);
+
+  store.set(metadataStoreState.atomFamily('objectMetadataItems'), {
+    current: flatObjects,
+    draft: [],
+    status: 'up-to-date',
+  });
+
+  store.set(metadataStoreState.atomFamily('fieldMetadataItems'), {
+    current: flatFields,
+    draft: [],
+    status: 'up-to-date',
+  });
+
+  store.set(metadataStoreState.atomFamily('indexMetadataItems'), {
+    current: flatIndexes,
+    draft: [],
+    status: 'up-to-date',
+  });
+};