@@ -0,0 +1,22 @@
+---
+'@objectstack/formula': patch
+'@objectstack/service-automation': patch
+'@object-ui/core': patch
+'@object-ui/react': patch
+---
+
+fix(formula,core,react): a template's formatter locale comes from a reserved context channel, so a root named `locale` is just a value, and the console passes the viewer's display locale
+
+Clause-②: yes (narrowing)
+Metadata-protocol: none
+
+<!-- adr-0087: not-required (no-migration-prescription) No metadata moves: no spec key, authorable spelling, object definition, stored row or stored shape is added, removed, renamed or re-shaped. What changes is which input sets the template dialect's formatter locale: the evaluate context's own `locale` field instead of a root named `locale`. A template that names a root `locale` keeps compiling and rendering; its hole still prints that value, only the number and date formatting no longer follows it. There is nothing for `objectstack migrate meta` to rewrite. The other categories are closed on facts: every package publishes (not unpublished); no ADR-0087 id is named or touched (not registered or already-registered); and no runtime interface, type or export is removed or narrowed: `EvalContext` gains an optional member and `fillTemplateHoles` an optional trailing argument (not runtime-interface-only, type-surface-only or runtime-export-retired). -->
+
+The `template` dialect's formatters (`number`, `currency`, `percent`, `date`, `datetime`) used to take their locale from `extra.locale`, the same bag a caller passes the template's roots in. A template's roots are author-visible values, so a bulk action param or a flow variable named `locale` silently set the locale of every formatted value in the sentence, and no caller ever passed the viewer's locale.
+
+- **`@objectstack/formula`**: `EvalContext` gains `locale?: string`, a reserved channel like `timezone`. It is not bound as a variable, and the template engine reads its formatter locale from it alone, defaulting to `en-US` when unset or empty. `extra.locale` is no longer read.
+- **`@objectstack/service-automation`**: a flow text slot's formatters render in `en-US`, and a flow variable named `locale` is a value like any other. The renderer's doc said the variable was also the formatters' locale; that line is gone.
+- **`@object-ui/core`**: `fillTemplateHoles(source, roots, locale?)` passes `locale` on the engine's reserved channel, apart from the roots. `ActionRunner.setDisplayLocale(read)` installs where the runner reads the viewer's display locale; `confirmText` and `successMessage` templates format in it, and a `callContext` dispatch keeps it.
+- **`@object-ui/react`**: `<ActionProvider>` and `useActionRunner` install `useDisplayLocale()` on the runner they build, read when a template is filled, so a locale switch reaches a runner built before it.
+
+**BREAKING** (a narrowing) for a caller that set the formatter locale through a root: a template evaluated with `extra: { locale }` (or a flow variable named `locale`) now formats in `en-US` and prints the value only where a hole names it. None was found in this repository: the one test that did so now passes `locale` on the context. What to do: pass the locale as the evaluate context's `locale` (`templateEngine.evaluate(expr, { extra: roots, locale })`), or as `fillTemplateHoles`'s third argument.
@@ -69,3 +69,38 @@ describe('templateEngine', () => {
     expect(r).toEqual({ ok: true, value: 'hot' });
   });
 });
+
+// The formatter locale rides the context's reserved `locale` channel, never a
+// root (#26232). Expected strings come from `Intl` itself, so a newer ICU in CI
+// cannot drift them.
+describe('templateEngine — formatter locale channel', () => {
+  const source = '{{ amount | number:2 }} · {{ due | date:long }} · {{ locale }}';
+  const roots = { amount: 1234567.5, due: '2031-05-06T12:00:00Z' };
+  const due = new Date('2031-05-06T12:00:00Z');
+  const expected = (tag: string, printed = '') =>
+    `${new Intl.NumberFormat(tag, { minimumFractionDigits: 2, maximumFractionDigits: 2 }).format(1234567.5)} · ` +
+    `${new Intl.DateTimeFormat(tag, { dateStyle: 'long' }).format(due)} · ${printed}`;
+  const render = (ctx: Parameters<typeof templateEngine.evaluate>[1]) =>
+    templateEngine.evaluate<string>({ dialect: 'template', source }, ctx);
+
+  it('formats in the locale the context names', () => {
+    expect(render({ extra: roots, locale: 'de-DE' })).toEqual({ ok: true, value: expected('de-DE') });
+    expect(expected('de-DE')).not.toBe(expected('en-US'));
+  });
+
+  it('a root named `locale` is a value a hole prints, not the formatter locale', () => {
+    expect(render({ extra: { ...roots, locale: 'de-DE' } })).toEqual({
+      ok: true,
+      value: expected('en-US', 'de-DE'),
+    });
+    expect(render({ extra: { ...roots, locale: 'de-DE' }, locale: 'fr-FR' })).toEqual({
+      ok: true,
+      value: expected('fr-FR', 'de-DE'),
+    });
+  });
+
+  it('no locale, or an empty one, renders en-US as before', () => {
+    expect(render({ extra: roots })).toEqual({ ok: true, value: expected('en-US') });
+    expect(render({ extra: roots, locale: '' })).toEqual({ ok: true, value: expected('en-US') });
+  });
+});
@@ -272,10 +272,9 @@ export const templateEngine: DialectEngine = {
     if (!check.ok) return check as EvalResult<T>;
 
     const scope = buildScope(ctx);
-    const locale =
-      (ctx.extra && typeof ctx.extra.locale === 'string' && ctx.extra.locale) ||
-      (typeof (ctx as { locale?: string }).locale === 'string' && (ctx as { locale?: string }).locale) ||
-      'en-US';
+    // Formatter locale: the context's reserved `locale` channel only, never a
+    // root — a root named `locale` is a value like any other (#26232).
+    const locale = typeof ctx.locale === 'string' && ctx.locale !== '' ? ctx.locale : 'en-US';
     // Reference timezone for `datetime` rendering (ADR-0053 Phase 2). Unset →
     // Intl uses the runtime zone, matching pre-Phase-2 behavior.
     const timeZone = typeof ctx.timezone === 'string' ? ctx.timezone : undefined;
@@ -285,7 +284,7 @@ export const templateEngine: DialectEngine = {
       if (!parsed) return _match; // compile already validated; defensive
       const value = resolvePath(scope, parsed.path);
       if (parsed.filter) {
-        return FORMATTERS[parsed.filter.name](value, parsed.filter.arg, locale as string, timeZone);
+        return FORMATTERS[parsed.filter.name](value, parsed.filter.arg, locale, timeZone);
       }
       return baseString(value);
     });
 
@@ -4,7 +4,7 @@ import { templateEngine, TEMPLATE_FORMATTERS, formatValue } from './template-eng
 function render(source: string, record: Record<string, unknown>, timezone?: string): string {
   const r = templateEngine.evaluate<string>(
     { dialect: 'template', source },
-    { record, extra: { locale: 'en-US' }, ...(timezone ? { timezone } : {}) },
+    { record, locale: 'en-US', ...(timezone ? { timezone } : {}) },
   );
   if (!r.ok) throw new Error(r.error.message);
   return r.value;
 
@@ -82,6 +82,19 @@ export interface EvalContext {
    * Defaults to `UTC` when unset. Calendar-day `date` rendering stays tz-naive.
    */
   timezone?: string;
+  /**
+   * Locale (BCP-47 tag, e.g. `zh-CN`) the `template` dialect's formatters
+   * render numbers, money, percents and dates in. Defaults to `en-US` when
+   * unset or empty.
+   *
+   * A reserved channel, like {@link timezone}: it is NOT bound as a variable,
+   * and nothing in {@link extra} or any other root sets it. A template's roots
+   * are author-visible values (a bulk action's params, a flow's variables), so
+   * a root named `locale` is just a value a hole can print — it used to also
+   * set the formatter locale of the whole sentence (objectstack#26232). The
+   * caller that knows the viewer's display locale passes it here.
+   */
+  locale?: string;
   /**
    * Current authenticated subject (hook / action / view contexts).
    *
 
@@ -102,8 +102,10 @@ export function textTemplateScope(variables: VariableMap): Record<string, unknow
  * Value→string is the engine's, defined per value (ADR-0032 §3): `null` /
  * absent renders nothing, an object or array renders as JSON, a `Date` as its
  * ISO text, and a formatter makes the rest explicit (`{{ amount | currency }}`,
- * `{{ due | date:iso }}`). A flow variable named `locale` is also the
- * formatters' locale — the engine reads its scope's `locale` for that.
+ * `{{ due | date:iso }}`). The formatters render in the engine's default
+ * `en-US`: a flow variable named `locale` is a value like any other, never the
+ * formatters' locale (#26232 — the engine reads that from its own reserved
+ * channel, not from a root).
  *
  * Absent in, absent out: a slot the author left unset — or one that renders
  * no text at all — returns `undefined`, so a screen falls back to its node
 
@@ -267,6 +267,13 @@ describe('#22110 — renderTextSlot, the one text renderer', () => {
     it('leaves a single-brace token as literal text — the doors refuse it before a run, so the renderer never reads it', () => {
         expect(renderTextSlot('Hello {record.name}', vars({ record: ACME }))).toBe('Hello {record.name}');
     });
+
+    it('a flow variable named `locale` is a value a hole prints, not the formatters\' locale (#26232)', () => {
+        // Expected text from `Intl` itself, so a newer ICU in CI cannot drift it.
+        const amount = new Intl.NumberFormat('en-US', { minimumFractionDigits: 2, maximumFractionDigits: 2 }).format(1234567.5);
+        expect(renderTextSlot('{{ amount | number:2 }} ({{ locale }})', vars({ amount: 1234567.5, locale: 'de-DE' })))
+            .toBe(`${amount} (de-DE)`);
+    });
 });
 
 /** This package's `src` — the runtime whose `$` variables the spec judge lists. */
 
@@ -1 +1 @@
-{"package":"ui/packages/core","sources":111,"sha256":"05fe45802fffcc482f95bad59a66279b70572f8757decd9770dc126f119dab2e","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}
+{"package":"ui/packages/core","sources":111,"sha256":"c2cf28d9a3a53535b8a328f099857f84b3ac90402fedc8b898a9266cb261f55c","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}
@@ -1 +1 @@
-{"package":"ui/packages/react","sources":70,"sha256":"e3ea09e281e39a1d3f30d87b199d3756e88d7ffb48f91a11e777b2806a8bddff","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}
+{"package":"ui/packages/react","sources":70,"sha256":"d89393cc7203be3bc88ea59d1a5e0ad6cbda588b8b8ad44baefed0a44da5d9d2","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}
@@ -1283,6 +1283,7 @@ export class ActionRunner {
   private paramCollectionHandler: ParamCollectionHandler | null;
   private resultDialogHandler: ResultDialogHandler | null;
   private translate: ((key: string, options: { defaultValue: string }) => string) | null;
+  private displayLocale: (() => string | undefined) | null;
 
   /**
    * Built-in dispatch, one entry per runnable action type.
@@ -1322,6 +1323,7 @@ export class ActionRunner {
     this.paramCollectionHandler = null;
     this.resultDialogHandler = null;
     this.translate = null;
+    this.displayLocale = null;
   }
 
   /**
@@ -1341,6 +1343,20 @@ export class ActionRunner {
     this.translate = translate;
   }
 
+  /**
+   * Set where the runner reads the viewer's display locale (a BCP-47 tag) —
+   * the host's own, injected so this package resolves none. It is read when a
+   * copy template is filled, so a language switch reaches a runner built
+   * before it. The `template` formatters in `confirmText` and
+   * `successMessage` render in it (`{{ amount | currency }}`,
+   * `{{ due | date:long }}`), through the engine's reserved locale channel, so
+   * a root named `locale` never sets it (objectstack#26232). With none
+   * installed they format in `en-US`.
+   */
+  setDisplayLocale(displayLocale: () => string | undefined): void {
+    this.displayLocale = displayLocale;
+  }
+
   /**
    * Set a custom confirmation handler (e.g., Shadcn AlertDialog).
    */
@@ -1811,7 +1827,11 @@ export class ActionRunner {
     const successCopy = actionCopySource(action.successMessage);
     if (successCopy !== undefined && successCopy.trim() !== '') {
       return hasTemplateHoles(successCopy)
-        ? fillTemplateHoles(successCopy, { result: payload, record: this.dispatchRecord(action) })
+        ? fillTemplateHoles(
+          successCopy,
+          { result: payload, record: this.dispatchRecord(action) },
+          this.displayLocale?.(),
+        )
         : successCopy;
     }
     return this.runnerText(RUNNER_TEXT.completedSuccessfully);
@@ -1846,7 +1866,11 @@ export class ActionRunner {
     const staticParams = params && typeof params === 'object' && !Array.isArray(params)
       ? Object.fromEntries(Object.entries(params).filter(([key]) => key !== '_rowRecord'))
       : undefined;
-    return fillTemplateHoles(text, { record: this.dispatchRecord(action), params: staticParams });
+    return fillTemplateHoles(
+      text,
+      { record: this.dispatchRecord(action), params: staticParams },
+      this.displayLocale?.(),
+    );
   }
 
   /**
@@ -2917,9 +2941,9 @@ export class ActionRunner {
   /**
    * A one-shot runner for {@link ActionRunner.execute}'s `callContext`
    * (objectui#13063): this runner's context with `callContext` merged over it,
-   * and this runner's handlers, translator and registries, shared rather than
-   * copied, so the dispatch confirms, collects params, toasts and navigates
-   * exactly as this runner does.
+   * and this runner's handlers, translator, display locale and registries,
+   * shared rather than copied, so the dispatch confirms, collects params,
+   * toasts and navigates exactly as this runner does.
    *
    * Two keys follow the merge rather than the base:
    *
@@ -2961,6 +2985,7 @@ export class ActionRunner {
     scoped.paramCollectionHandler = this.paramCollectionHandler;
     scoped.resultDialogHandler = this.resultDialogHandler;
     scoped.translate = this.translate;
+    scoped.displayLocale = this.displayLocale;
     return scoped;
   }
Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-{"package":"ui/packages/core","sources":111,"sha256":"05fe45802fffcc482f95bad59a66279b70572f8757decd9770dc126f119dab2e","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}`
	`1`	`+{"package":"ui/packages/core","sources":111,"sha256":"c2cf28d9a3a53535b8a328f099857f84b3ac90402fedc8b898a9266cb261f55c","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}`
Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-{"package":"ui/packages/react","sources":70,"sha256":"e3ea09e281e39a1d3f30d87b199d3756e88d7ffb48f91a11e777b2806a8bddff","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}`
	`1`	`+{"package":"ui/packages/react","sources":70,"sha256":"d89393cc7203be3bc88ea59d1a5e0ad6cbda588b8b8ad44baefed0a44da5d9d2","manifestSha256":"1f6e1ccb925a678eaa393f9091dfc7d0285e4e3626e0a5c61a5474687debabb7"}`