# Introduction
This PR introduces a centralized, strictly-typed **metadata side-effect
engine** that unifies how system metadata side effects are derived and
applied across both metadata entry points — the **metadata GraphQL API**
and the **application sync / manifest** flow — and migrates the first
side effect end-to-end: **a unique scalar field owns its backing
single-field `UNIQUE` index** (full create / update / delete lifecycle).
## New conventions
- **Engine-owned companions**: metadata flagged `isSystemSideEffect:
true` is owned by the engine. Its deletion is never inferred from
absence in a manifest — it results from PG-level cascade or from a
delete side effect (a side effect always has a cause, its parent
metadata).
- **Reserved deterministic identifiers**: apps cannot declare metadata
reusing an engine-owned deterministic `universalIdentifier`. Doing so
fails validation with `RESERVED_SYSTEM_UNIVERSAL_IDENTIFIER` (until an
explicit override API exists).
- **Record-native operation matrix**: the operation matrix is keyed by
`universalIdentifier` (`AllFlatEntityOperationRecordByMetadataName`)
instead of arrays, making parent resolution and deduplication O(1).
Array-based API callers are transpiled to records at the
validate-build-and-run boundary.
- Twenty-sdk user-facing experience with system fields will only be
related to overrides.
# What this PR does
## 1. Side-effect engine (foundation)
- `MetadataSideEffectEngineService.expandWithSideEffects(...)` takes the
intention-carrying record matrix and returns it expanded with derived
side effects, or a structured failure.
- Handlers are registered via a typed **decorator + registry** pattern
(`MetadataSideEffectHandler({ operation, metadataName, name, description
})`), with runtime duplicate-name detection. Multiple handlers per
(operation, metadataName) are supported.
- Handler contract mirrors the validator pattern:
- receives the trigger flat entity, the live record matrix, and
**strictly-typed related flat entity maps**
(`MetadataFlatEntityAndRelatedFlatEntityMapsForSideEffect<P>`, derived
from declared companion metadata names — no loose
`Partial<AllFlatEntityMaps>` context)
- returns `MetadataSideEffectResult`: `success` (operations record) |
`noop` | `fail` (structured failure)
- **Non-recursion is structural**: triggers are read from the original
caller input, never from the expanded matrix, so a side effect can never
trigger another side effect.
- **Deduplication + collision detection**: side effects are deduped by
`universalIdentifier` per operation; a caller-declared entity colliding
with an engine-owned deterministic identifier is recorded as a
collision.
- **Unified failure channel**: handler failures and reserved-identifier
collisions are merged into the same `OrchestratorFailureReport` contract
as builder validation errors, and the run short-circuits (fail-closed,
nothing is applied).
## 2. First migrated side effect — unique field → backing unique index
Three handlers own the complete lifecycle of the deterministic
single-field `UNIQUE` index backing a unique scalar field:
- **create**: unique scalar field → generate the deterministic backing
index (`fieldUniqueBackingIndexOnCreate`)
- **update**: `isUnique` flips and renames of still-unique fields (the
index name — and therefore its deterministic identifier — derives from
the field name, so a rename drops the stale index and recreates the
deterministic one) (`fieldUniqueBackingIndexOnUpdate`)
- **delete**: cascade-delete the backing index
(`fieldUniqueBackingIndexOnDelete`)
Supporting rules:
- The primary key `id` field never spawns a backing index (uniqueness
comes from the PK constraint) — explicit `isPrimaryKeyFlatFieldMetadata`
guard.
- Parent object resolution is **optimistic-first**: an object created or
updated in the same batch wins over the workspace cache (so e.g.
renaming an object while flipping a field to unique builds the index
from the post-rename object), resolved in O(1) via the record matrix.
- A missing parent object is reported as a structured side-effect
failure, never silently skipped.
## 3. Path convergence — manifest and API share one flow
- The manifest sync now derives a from→to **record matrix** from the
cache and feeds `validateBuildAndRunWorkspaceMigrationFromRecord`, the
same flow the API uses — both paths converge on the engine.
- Manifest-side unique-index generation and API transpiler
system-unique-index handling were removed (declared/composite/relation
indexes stay untouched).
- New `WorkspaceMigrationFlatEntityMapsService` mutualizes
flat-entity-maps computation between the side-effect engine and the
builder: cache keys are derived from the caller metadata names (+
validation- and side-effect-related closures) instead of hardcoded
loads.
- App-scoping and pruning are folded into one shared primitive
(`getSubAllFlatEntityMapsByApplicationIdsOrThrow`): slicing dependency
maps to the involved applications always prunes dangling one-to-many
aggregators — callers can no longer forget it.
- **Behavior change**: an app extending another app's view with a view
field now syncs successfully (cross-app view-field extension), covered
by a dedicated integration test.
## 4. Backfill upgrade command (2.19)
`upgrade:2-19:backfill-system-unique-index-universal-identifier`
rewrites legacy system unique-index `universalIdentifier`s to their
deterministic value so the engine can own pre-existing indexes. The
backfill is **driven from `isUnique: true` fields** (mirroring the
engine ownership predicate — excludes PK / morph / relation fields) and
resolves each field's backing index in O(1).
# Bugs fixed along the way
- `database:reset` seeding failed with
`INDEX_FIELD_INVALID_DEFAULT_VALUE`: the engine derived a backing
`UNIQUE` index for the default `id` primary key. Fixed with the explicit
primary-key guard.
- `isUnique` updates on system-flagged standard fields (e.g.
auto-created `name`) did not trigger the backing-index side effect.
- Manifest sync crashed with "Could not find flat entity with universal
identifier ..." when app-scoped slices left dangling aggregator
references — fixed by centralizing pruning in the shared slice primitive
Paul Rastoin
43730d7748