## Summary
Lets a Twenty application add **view fields (columns) to an existing
view it does not own** — including standard views like the People index
view — without redeclaring/owning that view. This mirrors the existing,
working pattern by which an app adds a custom field to a standard object
via `defineField` + `objectUniversalIdentifier`.
The asymmetry being removed was purely in the manifest schema:
`ViewFieldManifest` only existed *nested* inside
`ViewManifest.fields[]`, so adding a view field forced declaring a
`ViewManifest` — which the sync treats as a view the app creates and
owns, and rejects when the UID is a standard view's. Validation,
persistence, the FK aggregator machinery, and uninstall cleanup were
already generic and cross-app-safe, so no engine changes were needed.
### Changes
- **twenty-shared:** new top-level `StandaloneViewFieldManifest`
(`ViewFieldManifest & { viewUniversalIdentifier }`),
`Manifest.viewFields`, and a `SyncableEntity.ViewField` member.
- **twenty-sdk:** `defineViewField` (validates `universalIdentifier` +
`viewUniversalIdentifier` + `fieldMetadataUniversalIdentifier`), CLI
manifest assembly of a top-level `viewFields` list, and `dev:add
viewField` scaffolding.
- **twenty-server:** one top-level loop over `manifest.viewFields` that
reuses the existing `fromViewFieldManifestToUniversalFlatViewField`
converter (already parameterized by `viewUniversalIdentifier`). No
validator/persistence/aggregator changes.
### Notes for maintainers
- Confirm the `Manifest.viewFields` optionality convention — implemented
as a **required** array to mirror `fields`/`views`.
- Two different apps adding a column for the same field to the same view
conflicts on the existing unique `(fieldMetadataId, viewId)` partial
index; the existing `flat-view-field-validator` duplicate check surfaces
this as a structured validation error.
- `dev:add viewField` scaffolding is included (was optional in the
plan).
## Test Plan
- [x] `twenty-shared` typecheck
- [x] `twenty-sdk` 364 unit tests + `buildManifest` assembly test
(rich-app fixture) + typecheck + prettier
- [x] `twenty-server` typecheck + `lint:diff-with-main`
- [x] **Server integration suite**
`successful-manifest-update-view-field.integration-spec.ts` (4/4):
- standalone view field attaches to the standard `allPeople` view
without recreating it (sync succeeds, no
`INVALID_VIEW_DATA`/`ENTITY_ALREADY_EXISTS`)
- uninstall removes the contributed column while the standard view + its
columns remain intact
- duplicate `(view, field)` rejected with `METADATA_VALIDATION_FAILED`
- unknown target view rejected
- [x] Sibling `successful-manifest-update-field.integration-spec.ts`
still green (no harness regression)
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martmull
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