## Summary
Successive application syncs (`yarn twenty dev --once`) kept reporting
the same viewSorts as updated, even with no manifest changes. The
manifest converter never set `subFieldName`, so the manifest-derived
flat viewSort carried `undefined` where the flat viewSort computed from
the database carried `null`. The comparator (microdiff) treats `null` vs
`undefined` as a change, producing a phantom update action on every sync
that never converges — the resulting update is a no-op on the database.
Fixestwentyhq/core-team-issues#2629
## Changes
- **Converter**: `fromViewSortManifestToUniversalFlatViewSort` now sets
`subFieldName: viewSortManifest.subFieldName ?? null`, matching how the
sibling converters (e.g. view filters) handle optional compared
properties.
- **Type definition**: added optional `subFieldName?: string` to
`ViewSortManifest` in `twenty-shared`, mirroring `ViewFilterManifest` —
this also makes sorts on composite sub-fields (e.g. `amountMicros`)
expressible in app manifests, which the entity already supports.
- **Tests**:
- Asserts `subFieldName` is `null` (not `undefined`) when omitted — the
idempotency regression.
- Asserts `subFieldName` is passed through when provided.
## Verification
- All 12 application-manifest converter suites pass (47 tests).
- Flat-entity comparison/constants suites pass (36 tests, 21 snapshots).
- `subFieldName` was already part of the viewSort compare properties, so
no comparator/constants changes needed.
https://claude.ai/code/session_018FrD42MMQtu1UvDyiEZbSq
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martmull
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