@@ -0,0 +1,20 @@
+---
+'@objectstack/metadata-protocol': minor
+'@objectstack/cloud-connection': minor
+---
+
+fix(metadata-protocol)!: the override write gate judges an email template by its locale, so a `<base>.custom` override of a locale the base does not ship is refused (#28746)
+
+Clause-②: yes (narrowing)
+Metadata-protocol: narrowed
+
+<!-- adr-0087: not-required (no-migration-prescription) No key of any schema is added, removed, renamed or re-shaped: the override write gate (ADR-0146 D2) now counts the packages that ship an email template at the bundle member the body addresses, as the read side already serves it. A stored row this gate would refuse is not converted: it is served as before, and its next save meets the gate's own refusal with its remedy (drop `overrides`). -->
+
+**BREAKING** accept-set narrowing at the override write gate, with one widening beside it. An email template is one item per `(name, locale)` (`ITEM_KEY_DISCRIMINATORS`), but the gate asked which packages of the closure ship the template's NAME, across every locale.
+
+- **Narrowed.** A `<base>.custom` pair declaring `overrides: { package: <base> }` on a locale the base does not ship is refused `403 NOT_OVERRIDABLE` (`declared_package_ships_no_such_item`, the sentence now naming the locale) at the save door, at the per-item publish (`?member=`) and at a package publish, by `os validate` / `os build`, and at `POST /api/v1/marketplace/install-local`. It was admitted and served as an override, with no base member for drift detection or "Restore package original" to compare against. The remedy is in the sentence: remove `overrides` to keep it as the pair's own locale.
+- **Widened.** A locale the base does not ship, saved in the pair WITHOUT `overrides`, is the pair's own new member and is admitted at the same doors. It was refused `undeclared_same_name`, which told the author to declare an override of a member that does not exist. The same holds for a dependent package's template of a name its base ships in another locale: it collides with no base member.
+- **Unchanged.** A declared override of a locale the base ships is admitted; an undeclared same-locale item is still refused `undeclared_same_name`; every other type's identity is its name alone, as before; the read side already served per member.
+- **At rest.** A pair row stored before this release that declares an override of an unshipped locale keeps being served. Its next save carrying `overrides` is refused with the remedy; saved without `overrides`, it is the pair's own locale.
+
+`@objectstack/metadata-protocol` exports `overrideWriteIdentityOf(type, identity, item)`, the one identity the gate's callers compare shipped and incoming items on: an item's name (an action's `<objectName>:<name>`), joined with its bundle member for a pair-identified type. `OverrideWriteItem.identity` (from `overrideWriteItemsOf`) is spelled through it, so an email template's identity now carries its locale.
@@ -134,4 +134,48 @@ describe('#28410 — findOverrideDeclarationRefusals walks the artifact under th
     expect(rows.map((r) => r.rule)).toEqual(['declared_package_outside_closure']);
     expect(rows[0].message).toMatch(/Declare a dependency on 'com\.acme\.crm'/);
   });
+
+  // [#28746] An email template is one item per `(name, locale)`: the base
+  // below ships `crm_welcome` in `en-US` only, so each member is judged alone.
+  const templateBase = pkg(BASE, [], { emailTemplates: [{ name: 'crm_welcome', locale: 'en-US', subject: 'Welcome' }] });
+  const declared = { package: BASE, basedOn: '1.0.0' } as const;
+
+  it('[#28746] the pair declaring an override of a locale the base does not ship is refused', () => {
+    const rows = findOverrideDeclarationRefusals({
+      manifest: manifest('com.acme.bundle'),
+      packages: [templateBase, pkg(PAIR, [BASE], {
+        emailTemplates: [{ name: 'crm_welcome', locale: 'fr-FR', subject: 'Bienvenue', overrides: { ...declared } }],
+      })],
+    });
+    expect(rows.map((r) => [r.path, r.packageId, r.rule])).toEqual([
+      ['packages[1].manifest.emailTemplates[0]', PAIR, 'declared_package_ships_no_such_item'],
+    ]);
+  });
+
+  it('[#28746] controls: the pair overrides the shipped locale and adds an undeclared locale of its own', () => {
+    expect(findOverrideDeclarationRefusals({
+      manifest: manifest('com.acme.bundle'),
+      packages: [templateBase, pkg(PAIR, [BASE], {
+        emailTemplates: [
+          { name: 'crm_welcome', locale: 'en-US', subject: 'Ours', overrides: { ...declared } },
+          { name: 'crm_welcome', locale: 'fr-FR', subject: 'Bienvenue' },
+        ],
+      })],
+    })).toEqual([]);
+  });
+
+  it('[#28746] a dependent\'s template of the base\'s name collides only at a locale the base ships', () => {
+    const rows = findOverrideDeclarationRefusals({
+      manifest: manifest('com.acme.bundle'),
+      packages: [templateBase, pkg(PARTNER, [BASE], {
+        emailTemplates: [
+          { name: 'crm_welcome', locale: 'en-US', subject: 'Partner' },
+          { name: 'crm_welcome', locale: 'fr-FR', subject: 'Partenaire' },
+        ],
+      })],
+    });
+    expect(rows.map((r) => [r.path, r.rule])).toEqual([
+      ['packages[1].manifest.emailTemplates[0]', 'undeclared_same_name'],
+    ]);
+  });
 });
@@ -233,4 +233,35 @@ describe('install-local 2d — the override write gate at the managed install (A
         ]);
         expect(collisions[1].message).toMatch(/Declare it/);
     });
+
+    // [#28746] An email template is one item per `(name, locale)`: the base
+    // below ships `crm_welcome` in `en-US` only, so a member is judged alone.
+    const TEMPLATE_HOLDINGS: Holdings = {
+        [BASE]: { email_template: [{ name: 'crm_welcome', locale: 'en-US', subject: 'Welcome' }] },
+    };
+    const DECLARED = { package: BASE, basedOn: '1.0.0' } as const;
+
+    it('[#28746] the paired .custom declaring an override of a locale the base does not ship is refused 403, and nothing is written', async () => {
+        const { res, registered, ledger } = await install({
+            id: PAIR, version: '1.0.0', dependencies: deps(BASE),
+            emailTemplates: [{ name: 'crm_welcome', locale: 'fr-FR', subject: 'Bienvenue', overrides: { ...DECLARED } }],
+        }, [{ id: BASE }], TEMPLATE_HOLDINGS);
+        expect(res.status, JSON.stringify(res.payload)).toBe(403);
+        expect(res.payload?.error?.code).toBe('NOT_OVERRIDABLE');
+        expect(refusedOf(res)).toEqual([['email_template', 'crm_welcome', 'declared_package_ships_no_such_item']]);
+        expect(registered).toEqual([]);
+        expect(ledger).toEqual([]);
+    });
+
+    it('[#28746] CONTROL: the pair overrides the locale the base ships, and adds an undeclared locale of its own', async () => {
+        const { res, registered } = await install({
+            id: PAIR, version: '1.0.0', dependencies: deps(BASE),
+            emailTemplates: [
+                { name: 'crm_welcome', locale: 'en-US', subject: 'Ours', overrides: { ...DECLARED } },
+                { name: 'crm_welcome', locale: 'fr-FR', subject: 'Bienvenue' },
+            ],
+        }, [{ id: BASE }], TEMPLATE_HOLDINGS);
+        expect(res.status, JSON.stringify(res.payload)).toBe(200);
+        expect(registered).toEqual([PAIR]);
+    });
 });
@@ -245,7 +245,7 @@ import type {
 import { unmanagedInstallPostureRefusal, isWritablePackage, clientFacingFailureText, captureUninstallDeclared } from '@objectstack/metadata-protocol';
 // [ADR-0146 D2, #28410] The override write gate's one rule and its item walk,
 // asked at the managed install exactly as the publish doors ask them.
-import { judgeOverrideWrite, overrideWriteItemsOf, type OverrideWriteItem, type OverrideWriteRule } from '@objectstack/metadata-protocol';
+import { judgeOverrideWrite, overrideWriteIdentityOf, overrideWriteItemsOf, type OverrideWriteItem, type OverrideWriteRule } from '@objectstack/metadata-protocol';
 // [ADR-0146 D10, #28564] The `__c` extension-field reservation's one judge, step 1c''.
 import { judgeExtensionFieldSuffix } from '@objectstack/metadata-protocol';
 import { resolveThrownHttpError } from '@objectstack/types';
@@ -581,14 +581,20 @@ function listedItems(answer: unknown): Record<string, unknown>[] {
         : [];
 }
 
-/** An item's registry identity — `overrideWriteItemsOf`'s: an action is `<objectName>:<name>`. */
+/**
+ * An item's registry identity — `overrideWriteItemsOf`'s: an action is
+ * `<objectName>:<name>`, and [#28746] a pair-identified type's item carries its
+ * bundle member, through the gate's own `overrideWriteIdentityOf`, so an
+ * installed base's listed `en-US` template and an incoming `fr-FR` one are two
+ * items here as at the publish doors.
+ */
 function listedIdentity(type: string, item: Record<string, unknown>): string | undefined {
     const name = typeof item.name === 'string' && item.name !== '' ? item.name : undefined;
     if (name === undefined) return undefined;
     if (type === 'action' && typeof item.objectName === 'string' && item.objectName !== '' && !name.includes(':')) {
         return `${item.objectName}:${name}`;
     }
-    return name;
+    return overrideWriteIdentityOf(type, name, item);
 }
 
 /** A `{ … }` object — not an array, not null. */
 
@@ -34,7 +34,7 @@ export type { MetadataAuthoringChannel } from './protocol.js';
 // [ADR-0146 D2, #28410] The override write gate's one rule, exported for the
 // two gate points outside this package — `os validate` and the marketplace
 // managed install — so all three doors ask one judgement and cannot drift.
-export { judgeOverrideWrite, overrideWriteItemsOf, type OverrideWriteItem, type OverrideWriteSubject, type OverrideWriteClosure, type OverrideWriteRule, type OverrideWriteVerdict } from './protocol-packaged-base-refusal.js';
+export { judgeOverrideWrite, overrideWriteIdentityOf, overrideWriteItemsOf, type OverrideWriteItem, type OverrideWriteSubject, type OverrideWriteClosure, type OverrideWriteRule, type OverrideWriteVerdict } from './protocol-packaged-base-refusal.js';
 // [ADR-0146 D10, #28564] The `__c` extension-field reservation's one judge,
 // exported for the doors outside this package — `os validate` and the
 // marketplace install — so every door that lets a field in asks one judgement.
 
@@ -97,17 +97,17 @@ export function artifactLockLayerAt(
 /** The body of `ObjectStackProtocolImplementation#shippedArtifactsOf`; the method's docblock there is its contract. */
 export function shippedArtifactsOf(
     this: Pick<ArtifactLookupHost, 'lookupArtifactItem' | 'shippingPackagesOf'>,
-    type: string, name: string, shipping?: ShippingPackages,
+    type: string, name: string, shipping?: ShippingPackages, member?: string,
 ): unknown[] {
     const shipped: unknown[] = [];
     const add = (artifact: unknown): void => {
         if (artifact !== undefined && artifact !== null && !shipped.includes(artifact)) shipped.push(artifact);
     };
-    add(this.lookupArtifactItem(type, name));
+    add(this.lookupArtifactItem(type, name, undefined, member));
     if ((PLURAL_TO_SINGULAR[type] ?? type) === 'object') return shipped;
     const packages = shipping ?? this.shippingPackagesOf(type);
     for (const packageId of new Set([...(packages.byName.get(name) ?? []), ...packages.anyName])) {
-        const own = this.lookupArtifactItem(type, name, packageId) as { _packageId?: unknown } | undefined;
+        const own = this.lookupArtifactItem(type, name, packageId, member) as { _packageId?: unknown } | undefined;
         if (own?._packageId === packageId) add(own);
     }
     return shipped;
 
@@ -47,6 +47,7 @@ import {
 } from '@objectstack/spec/kernel';
 import { PLURAL_TO_SINGULAR } from '@objectstack/spec/shared';
 import { expandViewContainer, isAggregatedViewContainer } from '@objectstack/spec';
+import { ITEM_KEY_DISCRIMINATORS, itemDiscriminator } from '@objectstack/metadata-core';
 
 /**
  * The `ObjectStackProtocolImplementation` members the functions below read —
@@ -266,6 +267,40 @@ export function isPairRowRemoval(type: string, basePackageId: unknown, packageId
     return pair.ok && pair.value === packageId;
 }
 
+/**
+ * [#28746, ADR-0146 D2] The bundle member an item IS, for a type whose
+ * identity is a pair (`ITEM_KEY_DISCRIMINATORS`: an `email_template` is one
+ * item per `(name, locale)`), the canonical member when the body declares
+ * none; `undefined` for every other type, whose identity is its name alone.
+ *
+ * Read off the identity table the registry keys its bundles on and the read
+ * side serves a member by (`findServedOverlayRow`, the layered read), never a
+ * type literal. The save is BODY-addressed, so the member is the body's own.
+ */
+export function overrideWriteMemberOf(type: string, item: unknown): string | undefined {
+    return itemDiscriminator(PLURAL_TO_SINGULAR[type] ?? type, item);
+}
+
+/**
+ * [#28746, ADR-0146 D2] The identity two packages' items collide on under the
+ * override write gate: `identity` (an item's name; an `action`'s
+ * `<objectName>:<name>`) joined with its bundle member
+ * ({@link overrideWriteMemberOf}) for a pair-identified type, and `identity`
+ * unchanged for every other type.
+ *
+ * The ONE spelling every door that hands the gate its `shippers` compares on:
+ * {@link overrideWriteItemsOf} (so `os validate` and the install door's
+ * incoming items), the install door's listing of an installed package, and
+ * {@link overrideWriteVerdict}'s registry lookup at the same member. A base
+ * that ships a template in `en-US` alone therefore ships no `fr-FR` member: a
+ * declared `fr-FR` override is refused (`declared_package_ships_no_such_item`),
+ * and an undeclared `fr-FR` beside it collides with nothing.
+ */
+export function overrideWriteIdentityOf(type: string, identity: string, item: unknown): string {
+    const member = overrideWriteMemberOf(type, item);
+    return member === undefined ? identity : `${identity}\u0000${member}`;
+}
+
 /** One item written into one package — what the override write gate judges. */
 export interface OverrideWriteSubject {
     /** The metadata type, either spelling (folded here). */
@@ -287,7 +322,11 @@ export interface OverrideWriteClosure {
      * admitting needs the base to be proven inside the closure.
      */
     readonly dependencies: readonly string[] | undefined;
-    /** The packages of {@link dependencies} that ship an item of this type and name. */
+    /**
+     * The packages of {@link dependencies} that ship an item of this type and
+     * name — for a pair-identified type, of this bundle member
+     * ({@link overrideWriteIdentityOf}).
+     */
     readonly shippers: readonly string[];
 }
 
@@ -350,7 +389,8 @@ function declarationOf(item: unknown): { present: boolean; base: string | undefi
  * Order: a declaration is judged on its type first (D10 `object`, D6 and the
  * other excluded types, then D9's `flow` and `action`), then on who declares
  * (the pair alone), then on what it names (inside the closure, and shipping
- * that item). An undeclared item is judged only when a package of its closure
+ * that item — for a pair-identified type, that bundle member: the caller's
+ * `shippers` are counted at {@link overrideWriteIdentityOf}). An undeclared item is judged only when a package of its closure
  * ships the same name, on a type a declared override applies to; outside the
  * closure two packages keep ADR-0048 §3.3/§3.4's coexistence on a bare name.
  */
@@ -406,8 +446,11 @@ export function judgeOverrideWrite(
                 + `Declare a dependency on '${base}' in the \`dependencies\` of '${packageId}''s manifest, or remove \`overrides\` (ADR-0146 D2).`);
         }
         if (!closure.shippers.includes(base)) {
+            // [#28746] A pair-identified type names the member it addressed.
+            const member = overrideWriteMemberOf(type, subject.item);
+            const ofMember = member === undefined ? '' : ` with ${ITEM_KEY_DISCRIMINATORS[type]?.field} '${member}'`;
             return refuse('declared_package_ships_no_such_item',
-                `${item} declares an override of '${base}', which ships no ${type} named '${name}'. `
+                `${item} declares an override of '${base}', which ships no ${type} named '${name}'${ofMember}. `
                 + `Remove \`overrides\` to keep it as '${packageId}''s own item, or correct the name (ADR-0146 D2).`);
         }
         return { verdict: 'admit', base };
@@ -438,7 +481,9 @@ export interface OverrideWriteItem {
     readonly name: string;
     /**
      * The registry identity two packages collide on: an `action` is
-     * `<objectName>:<name>` (the registry's key), every other item its name.
+     * `<objectName>:<name>` (the registry's key), every other item its name,
+     * and [#28746] a pair-identified type's item that joined with its bundle
+     * member ({@link overrideWriteIdentityOf}).
      */
     readonly identity: string;
     /** The item body the declaration is read from. */
@@ -480,7 +525,7 @@ export function overrideWriteItemsOf(body: Record<string, unknown>, at = ''): Ov
             const identity = type === 'action' && typeof item.objectName === 'string' && item.objectName !== ''
                 ? `${item.objectName}:${declaredName}`
                 : declaredName;
-            out.push({ type, name: declaredName, identity, item, path });
+            out.push({ type, name: declaredName, identity: overrideWriteIdentityOf(type, identity, item), item, path });
         }
     }
     return out;
@@ -505,6 +550,11 @@ export function overrideWriteRefusalError(
  * registry (`resolveWritePackageScope`, the save door's own) and the shipping
  * packages from the artifact lookup (`shippedArtifactsOf`, the read's own),
  * then asks {@link judgeOverrideWrite}.
+ *
+ * [#28746] For a pair-identified type the lookup is at the body's bundle
+ * member ({@link overrideWriteMemberOf}), and an artifact of another member is
+ * no shipper: a registry that ignores `member` can answer one, as
+ * `mergeArtifactProtection` guards on the read side.
  */
 export function overrideWriteVerdict(
     this: Pick<PackagedBaseRefusalHost, 'isWritablePackage' | 'resolveWritePackageScope' | 'shippedArtifactsOf'>,
@@ -522,10 +572,12 @@ export function overrideWriteVerdict(
     // fact about the package, not about the item.
     if (packageId !== undefined && scope === undefined) return NOT_CONCERNED;
     const dependencies = scope?.dependencies.filter((id) => id !== packageId);
+    const member = overrideWriteMemberOf(request.type, request.item);
     const shippers = dependencies === undefined || dependencies.length === 0
         ? []
         : Array.from(new Set(
-            this.shippedArtifactsOf(request.type, request.name)
+            this.shippedArtifactsOf(request.type, request.name, undefined, member)
+                .filter((a) => overrideWriteMemberOf(request.type, a) === member)
                 .map((a) => (a as { _packageId?: unknown } | null | undefined)?._packageId)
                 // An override replaces an item of an INSTALLED, read-only base
                 // (ADR-0146 D1): a writable package's item is edited in place