refactor(sql-orm-client): canonicalise cardinality tag from 'M:N' to 'N:M'

The SQL contract already emits 'N:M' (landed in D1). sql-orm-client was the
lone holdout still spelling it 'M:N', meaning a real emitted M:N relation
parsed to undefined and the mutation guard silently never fired.

Flip all four literal sites in src/:
- RelationCardinalityTag union (types.ts)
- partitionByOwnership guard + error message (mutation-executor.ts)
- IsToManyRelation type-level check (collection-internal-types.ts)
- parseRelationCardinality acceptance check (collection-contract.ts)

Update tests to match: move the rejection test's cardinality literal to
'N:M' (stays a rejection test), update the guard error message regex,
and update the isToOneCardinality argument in collection-contract.test.ts
(required for typecheck: 'M:N' is no longer assignable to
RelationCardinalityTag).

Signed-off-by: Alexey Orlenko's AI Agent <robot@aqrln.net>

Author: tensordreams

packages/3-extensions/sql-orm-client/src/collection-contract.ts

@@ -298,7 +298,7 @@ export function resolveModelRelations(
 }
 
 export function parseRelationCardinality(value: unknown): RelationCardinalityTag | undefined {
-  if (value === '1:1' || value === 'N:1' || value === '1:N' || value === 'M:N') {
+  if (value === '1:1' || value === 'N:1' || value === '1:N' || value === 'N:M') {
     return value;
   }
   return undefined;

packages/3-extensions/sql-orm-client/src/collection-internal-types.ts

@@ -83,7 +83,7 @@ export type IsToManyRelation<
   TContract extends Contract<SqlStorage>,
   ModelName extends string,
   RelName extends string,
-> = RelationCardinality<TContract, ModelName, RelName> extends '1:N' | 'M:N' ? true : false;
+> = RelationCardinality<TContract, ModelName, RelName> extends '1:N' | 'N:M' ? true : false;
 
 export type IncludeRefinementResult<
   TContract extends Contract<SqlStorage>,

packages/3-extensions/sql-orm-client/src/mutation-executor.ts

@@ -348,8 +348,8 @@ function partitionByOwnership(relationMutations: readonly ParsedRelationMutation
       continue;
     }
 
-    if (relationMutation.relation.cardinality === 'M:N') {
-      throw new Error('M:N nested mutations are not supported yet');
+    if (relationMutation.relation.cardinality === 'N:M') {
+      throw new Error('N:M nested mutations are not supported yet');
     }
 
     childOwned.push(relationMutation);

packages/3-extensions/sql-orm-client/src/types.ts

@@ -106,7 +106,7 @@ export interface CollectionTypeState {
   readonly variantName: string | undefined;
 }
 
-export type RelationCardinalityTag = '1:1' | 'N:1' | '1:N' | 'M:N';
+export type RelationCardinalityTag = '1:1' | 'N:1' | '1:N' | 'N:M';
 
 export type DefaultCollectionTypeState = {
   readonly hasOrderBy: false;

packages/3-extensions/sql-orm-client/test/collection-contract.test.ts

@@ -222,7 +222,7 @@ describe('collection-contract capability detection', () => {
     expect(isToOneCardinality('1:1')).toBe(true);
     expect(isToOneCardinality('N:1')).toBe(true);
     expect(isToOneCardinality('1:N')).toBe(false);
-    expect(isToOneCardinality('M:N')).toBe(false);
+    expect(isToOneCardinality('N:M')).toBe(false);
     expect(isToOneCardinality(undefined)).toBe(false);
   });
 

packages/3-extensions/sql-orm-client/test/mutation-executor.test.ts

@@ -405,7 +405,7 @@ describe('mutation-executor', () => {
             ...user.relations,
             posts: {
               ...user.relations.posts,
-              cardinality: 'M:N',
+              cardinality: 'N:M',
             },
           },
         },
@@ -425,7 +425,7 @@ describe('mutation-executor', () => {
             posts.connect({ id: 10 }),
         } as never,
       }),
-    ).rejects.toThrow(/M:N nested mutations are not supported yet/);
+    ).rejects.toThrow(/N:M nested mutations are not supported yet/);
   });
 
   it('executeNestedCreateMutation() supports parent-owned nested create() payloads', async () => {