diff --git a/‎.changeset/18056-email-template-locale-rungs.md‎
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diff --git a/‎.changeset/email-template-locale-floor.md‎
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diff --git a/‎content/docs/references/system/email-template.mdx‎
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diff --git a/‎packages/spec/src/contracts/email-service.ts‎
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diff --git a/‎packages/spec/src/stack-email-template-locale-floor.test.ts‎
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@@ -0,0 +1,51 @@
+---
+'@objectstack/spec': minor
+---
+
+docs(spec): scope the email-template locale-floor claims to a call that NAMES a locale (#18056)
+
+Clause-②: yes — no accept set moves (no key is added, removed or revalidated),
+but what a PUBLISHED package states about its own resolution contract is
+corrected, which is a contract act in substance.
+
+`packages/spec` stated two different rung counts for one resolution.
+`EmailTemplateDefinitionSchema.locale`'s `describe` and the
+`EMAIL_TEMPLATE_FLOOR_LOCALE` docblock published **one** retry rung and an
+explicit "no fallback floor at all"; `SendTemplateInput.locale` in
+`contracts/email-service.ts`, same package, documents a **three-rung** ladder
+whose third rung is reachable exactly on the path the first says cannot exist.
+
+Measured against the runtime rather than reconciled by preference —
+`EmailService.resolveAndRenderTemplate` and `createSysEmailTemplateLoader` in
+`@objectstack/plugin-email`, and the CI pins in
+`template-locale-resolution.test.ts` — the three-rung text is the correct one:
+
+1. the named locale, matched exactly (no language-subtag folding);
+2. the literal `en-US`, which is also where a call naming no locale starts;
+3. **only for a call that named no locale**, and only when the bundle carries
+   no `en-US` row: the bundle's lowest locale tag.
+
+So a bundle with no `en-US` row dead-letters (`TEMPLATE_NOT_FOUND`, permanent)
+for every recipient whose locale was NAMED, and silently renders whichever
+language sorts first for every call that named none. The shipped declaration
+promised the loud permanent refusal on the path where the runtime performs the
+silent fill; an author reading it was told a missing locale always
+dead-letters. Both call shapes are now named wherever the floor is claimed, and
+the ladder itself is stated in one place only.
+
+Also corrected: `SendTemplateInput.template` said the service "picks the
+best-matching locale row", which the resolver has never done — there is no
+best match and no folding, only the ladder above.
+
+`defineStack`'s `warnEmailTemplateLocaleFloor` gains a declaration of the two
+shapes it deliberately does NOT examine (a stack whose `i18n.supportedLocales`
+is absent or empty; a bundle whose tags all fall outside `supportedLocales`) —
+both can still ship a floorless bundle. Its control flow is unchanged — the same
+bundles warn, once each, and the warning stays advisory — but the emitted warning
+TEXT did change, and now names BOTH call shapes: it says the bundle has no
+fallback floor *for a send that names a locale*, and adds that a send naming NO
+locale does not fail but drops to that bundle's lowest tag and renders it
+silently. A test asserting on the old wording needs updating. Whether either
+undeclared shape should warn is the ADR-0049 enforce-or-remove question and is
+not answered here. Both shapes are now pinned against a warning discriminator so
+neither can change without a test saying so.
@@ -4,19 +4,22 @@
 
 Email templates: say where the `en-US` fallback floor is, and report a bundle that has none.
 
-`IEmailService.sendTemplate` matches `(name, locale)` exactly and retries exactly one rung —
-the literal `en-US`. There is no language-subtag folding, so a bundle whose English row is
-tagged `en` is unreachable from `en-US` and from every other tag it does not itself carry;
-each such delivery raises `TEMPLATE_NOT_FOUND`, which classifies permanent, so it dead-letters
-with no retry. An app declaring `i18n.defaultLocale: 'en'` and authoring `locale: 'en'` has
-done the consistent thing throughout and still shipped a bundle with no floor — and it
-validated, built and installed clean.
+`IEmailService.sendTemplate` matches `(name, locale)` exactly and, for a call that NAMES a
+locale, retries exactly one rung — the literal `en-US` — and stops. There is no language-subtag
+folding, so a bundle whose English row is tagged `en` is unreachable from `en-US` and from every
+other tag it does not itself carry; each such delivery raises `TEMPLATE_NOT_FOUND`, which
+classifies permanent, so it dead-letters with no retry. An app declaring
+`i18n.defaultLocale: 'en'` and authoring `locale: 'en'` has done the consistent thing throughout
+and still shipped a bundle with no floor for those calls — and it validated, built and installed
+clean.
 
 - `EmailTemplateDefinitionSchema.locale`'s `describe` and TSDoc now state the exact match, the
-  single literal `en-US` rung, the absence of folding, and that the stack's own declared default
-  locale is the wrong tag whenever it is not spelled `en-US`.
+  one literal `en-US` rung a call that NAMES a locale gets, the absence of folding, and that the
+  stack's own declared default locale is the wrong tag whenever it is not spelled `en-US`.
 - New exported `EMAIL_TEMPLATE_FLOOR_LOCALE` names that tag once: it is both the schema default
-  and the resolver's sole retry rung.
+  and the rung `sendTemplate` retries for a call that NAMES a locale. The full ladder — including
+  the lowest-tag rung reachable only by a call that names NO locale — is on
+  `SendTemplateInput.locale` in `packages/spec/src/contracts/email-service.ts`.
 - `defineStack` now reports (advisory `console.warn`, warn-once per bundle) an `emailTemplates`
   bundle that carries rows for the stack's own `i18n.supportedLocales` but none tagged `en-US`.
 
 
@@ -44,7 +44,7 @@ const result = EmailTemplateDefinitionSchema.parse(data);
 | **name** | `string` | ✅ | Template identifier (dotted snake_case) |
 | **label** | `string` | ✅ | Display label |
 | **category** | `Enum<'auth' \| 'notification' \| 'workflow' \| 'marketing' \| 'custom'>` | optional (default: `"custom"`) |  |
-| **locale** | `string` | optional (default: `"en-US"`) | BCP-47 locale (e.g. en-US, zh-CN) — the bundle key the resolver matches EXACTLY, with one retry rung: the literal `en-US`. No language-subtag folding, so `en` and `en-US` are different bundles and neither reaches the other. A bundle with no `en-US` row therefore has no fallback floor: any recipient locale it does not carry a row for raises TEMPLATE_NOT_FOUND, which is permanent — the delivery dead-letters with no retry. Your stack's own `i18n.defaultLocale` is the wrong tag here unless it is spelled `en-US`. |
+| **locale** | `string` | optional (default: `"en-US"`) | BCP-47 locale (e.g. en-US, zh-CN) — the bundle key the resolver matches EXACTLY. A call that NAMES a locale gets exactly one retry rung, the literal `en-US`, with no language-subtag folding: `en` and `en-US` are different ROWS of one bundle and neither reaches the other, so a bundle with no `en-US` row has no fallback floor for those calls and every recipient locale it does not carry a row for raises TEMPLATE_NOT_FOUND, which is permanent — the delivery dead-letters with no retry. A call naming NO locale is the other case and does not dead-letter: it drops to the bundle's lowest locale tag and renders that silently. Your stack's own `i18n.defaultLocale` is the wrong tag here unless it is spelled `en-US`. |
 | **subject** | `string` | ✅ | Subject template |
 | **bodyHtml** | `string` | ✅ | HTML body template |
 | **bodyText** | `string` | optional | Plain-text body template (auto-derived from HTML when omitted) |
 
@@ -150,8 +150,9 @@ export interface SendEmailResult {
 export interface SendTemplateInput {
   /**
    * Template identifier (matches `sys_email_template.name`), e.g.
-   * `'auth.password_reset'`. The service picks the best-matching
-   * locale row (falls back to `en-US`).
+   * `'auth.password_reset'`. There is no "best match" and no language-subtag
+   * folding: the locale row is resolved by the exact ladder documented on
+   * `locale` below.
    */
   template: string;
   /** Envelope recipients. */
 
@@ -1,7 +1,7 @@
 // Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
 //
 // #17614 — an `emailTemplates` bundle tagged with the stack's OWN
-// `i18n.defaultLocale` has no fallback floor.
+// `i18n.defaultLocale` has no fallback floor for a send that names a locale.
 //
 // Measured before this landed, on an unmodified tree: a stack declaring
 // `defaultLocale: 'en'`, `supportedLocales: ['en','zh-CN','ja-JP','es-ES']`
@@ -10,10 +10,13 @@
 // PERMANENT, so the delivery dead-letters with no retry — for `de-DE` and for
 // the literal `en-US`. The identical bundle with its English row tagged
 // `en-US` delivered for `de-DE`. `sendTemplate` matches `(name, locale)`
-// exactly and retries exactly one rung, the literal `en-US`; there is no
-// language-subtag folding, and that ladder's shape is a settled ruling this
-// change deliberately does not touch. The remedy is the bundle, so the
-// diagnostic is where the author is standing.
+// exactly and, for a call that NAMES a locale, retries exactly one rung — the
+// literal `en-US` — and stops; there is no language-subtag folding. A call that
+// names NO locale is the other case and does NOT dead-letter: it starts at
+// `en-US` by name and, when the bundle carries no `en-US` row, drops to that
+// bundle's lowest locale tag and renders it silently. That ladder's shape is a
+// settled ruling this change deliberately does not touch. The remedy is the
+// bundle, so the diagnostic is where the author is standing.
 //
 // These pin the diagnostic ADVISORY: every case asserts the parse still
 // succeeds and the stack comes back unchanged. The diagnostic narrows what
@@ -77,6 +80,23 @@ describe('#17614 — the floor tag is one named constant, not two spellings', ()
     expect(text).toContain('en-US');
     expect(text).toContain('TEMPLATE_NOT_FOUND');
   });
+
+  // [#18056] The same `describe` used to promise that a floorless bundle
+  // dead-letters, full stop. Measured against `EmailService`'s ladder
+  // (`resolveAndRenderTemplate` → `createSysEmailTemplateLoader`), that is true
+  // only for a call that NAMED a locale: a call naming none drops to the
+  // bundle's lowest tag and renders it, which `plugin-email`'s
+  // `template-locale-resolution.test.ts` pins as resolving, not dead-lettering.
+  // A published declaration promising a loud permanent refusal where the
+  // runtime performs a silent fill is the defect; both call shapes must stay
+  // named, so the promise cannot quietly go unconditional again.
+  it('[#18056] scopes the dead-letter promise to a call that NAMES a locale, and states the other case', () => {
+    const text = String(EmailTemplateDefinitionSchema.shape.locale.description ?? '');
+    expect(text).toMatch(/NAMES a locale/);
+    expect(text).toMatch(/lowest locale tag/);
+    // ⛔ The unscoped promise itself, in the spelling it shipped in.
+    expect(text).not.toMatch(/therefore has no fallback floor: any recipient locale/);
+  });
 });
 
 describe('#17614 — defineStack reports a bundle with no `en-US` floor', () => {
@@ -111,6 +131,11 @@ describe('#17614 — defineStack reports a bundle with no `en-US` floor', () =>
 });
 
 describe('#17614 — and stays silent where the bundle HAS a floor (the controls)', () => {
+  // ⛔ Every case in THIS block is a bundle that genuinely carries the floor
+  // row. The shapes that are floorless and silent anyway are the guard's scope
+  // boundary and live in their own block below — filing them here read as
+  // "these have a floor", which is exactly the kind of sentence about runtime
+  // behaviour nobody re-reads (#18056).
   it('silent when the bundle carries an en-US row beside the supported tags', () => {
     const { warns, value } = warningsOf(stack(
       ['en-US', 'zh-CN', 'ja-JP', 'es-ES'].map((l) => tpl(l)), THE_TRAP,
@@ -129,20 +154,97 @@ describe('#17614 — and stays silent where the bundle HAS a floor (the controls
     expect(value.emailTemplates?.[0]?.locale).toBe(EMAIL_TEMPLATE_FLOOR_LOCALE);
   });
 
-  it('silent when the stack declares no supportedLocales to measure against', () => {
-    const { warns } = warningsOf(stack([tpl('en')]));
-    expect(floorWarns(warns)).toEqual([]);
-  });
-
-  it('silent when no authored tag is one this stack claims to support', () => {
-    const { warns } = warningsOf(stack([tpl('fr-CA')], { defaultLocale: 'en', supportedLocales: ['en'] }));
-    expect(floorWarns(warns)).toEqual([]);
-  });
+});
 
+describe('#17614 — warn-once bookkeeping', () => {
   it('warns once for one bundle, however many times the same stack is defined', () => {
     const first = warningsOf(stack([tpl('pt-BR')], { defaultLocale: 'pt-BR', supportedLocales: ['pt-BR'] }));
     const second = warningsOf(stack([tpl('pt-BR')], { defaultLocale: 'pt-BR', supportedLocales: ['pt-BR'] }));
     expect(floorWarns(first.warns)).toHaveLength(1);
     expect(floorWarns(second.warns)).toEqual([]);
   });
 });
+
+// ── #18056 — the two shapes the guard returns early on ──────────────────────
+//
+// ⛔ NOT controls. Every bundle below genuinely carries NO `en-US` row, so the
+// hazard is real and the silence is this guard's DECLARED SCOPE, not a pass.
+// `warnEmailTemplateLocaleFloor`'s docblock now states both; these hold it to
+// that, in both directions — each silent case is paired with a DISCRIMINATOR
+// that warns, so "silent" can never be read out of a harness that had simply
+// stopped reporting. Whether either shape SHOULD warn is the ADR-0049
+// enforce-or-remove question and is not decided here; what is closed is the
+// silence being undeclared and unpinned.
+
+describe('#18056 — the guard\'s declared scope boundary', () => {
+  it('early return 1: a stack with no `i18n` block is never examined, floorless or not', () => {
+    const { warns, value } = warningsOf(stack([tpl('en', 'acme.scope_no_i18n')]));
+    expect(floorWarns(warns)).toEqual([]);
+    // …and the bundle really is floorless: one row, tagged `en`, no `en-US`.
+    expect(value.emailTemplates?.map((t) => t.locale)).toEqual(['en']);
+
+    // DISCRIMINATOR — the identical floorless bundle, under a stack that does
+    // declare the tag. The guard is awake; shape alone decides.
+    const seen = warningsOf(stack(
+      [tpl('en', 'acme.scope_no_i18n_disc')], { defaultLocale: 'en', supportedLocales: ['en'] },
+    ));
+    expect(floorWarns(seen.warns)).toHaveLength(1);
+  });
+
+  it('early return 1: `supportedLocales: []` is the other arm — `i18n` cannot omit the key', () => {
+    // Measured: `supportedLocales` is REQUIRED inside `i18n`, so the
+    // `!Array.isArray` arm is reachable only by omitting `i18n` entirely and
+    // the `length === 0` arm only by a literal empty array. Both are silent.
+    const { warns } = warningsOf(stack(
+      [tpl('en', 'acme.scope_empty_supported')], { defaultLocale: 'en', supportedLocales: [] },
+    ));
+    expect(floorWarns(warns)).toEqual([]);
+  });
+
+  it('early return 1 guards the read as much as it scopes — defineStack must not throw', () => {
+    // What deleting it actually costs. `supported.map(...)` off an absent
+    // `i18n` is a TypeError out of `defineStack` itself, and BOTH in-tree
+    // stacks that declare `emailTemplates` would take it (measured 2026-09-16:
+    // examples/app-showcase and the qa/dogfood materialization fixture).
+    expect(() => defineStack(stack([tpl('en', 'acme.scope_nothrow')]))).not.toThrow();
+  });
+
+  it('early return 2: a bundle whose tags are ALL outside supportedLocales is skipped', () => {
+    const i18n = { defaultLocale: 'en-GB', supportedLocales: ['en-GB'] };
+    const { warns, value } = warningsOf(stack([tpl('fr-CA', 'acme.scope_outside')], i18n));
+    expect(floorWarns(warns)).toEqual([]);
+    expect(value.emailTemplates?.map((t) => t.locale)).toEqual(['fr-CA']);
+
+    // DISCRIMINATOR — same stack, same floorlessness, one tag moved INSIDE
+    // `supportedLocales`. So the silence above is `declared` being empty, one
+    // line after the floor check established the bundle has no floor row.
+    const seen = warningsOf(stack([tpl('en-GB', 'acme.scope_inside')], i18n));
+    expect(floorWarns(seen.warns)).toHaveLength(1);
+    expect(floorWarns(seen.warns)[0]).toContain("carries rows for 'en-GB'");
+  });
+
+  it('early return 1 decides nothing early return 2 would not — the outcomes are equal', () => {
+    // Measured (#18056): with no supported set every bundle's `declared` list
+    // is empty, so shape 2 skips exactly what shape 1 returns before reaching.
+    // Pinning the OUTCOMES equal means a future change that gives shape 1 its
+    // own meaning has to come and say so here rather than landing silently.
+    const tags = (n: string) => [tpl('en', n), tpl('zh-CN', n)];
+    const noI18n = warningsOf(stack(tags('acme.scope_shadow_a')));
+    const emptySupported = warningsOf(stack(
+      tags('acme.scope_shadow_b'), { defaultLocale: 'en', supportedLocales: [] },
+    ));
+    const allOutside = warningsOf(stack(
+      tags('acme.scope_shadow_c'), { defaultLocale: 'ja-JP', supportedLocales: ['ja-JP'] },
+    ));
+    expect(floorWarns(noI18n.warns)).toEqual([]);
+    expect(floorWarns(emptySupported.warns)).toEqual([]);
+    expect(floorWarns(allOutside.warns)).toEqual([]);
+
+    // DISCRIMINATOR for all three: the same two-row floorless bundle, with its
+    // tags declared. One `supportedLocales` edit is the whole difference.
+    const seen = warningsOf(stack(
+      tags('acme.scope_shadow_d'), { defaultLocale: 'en', supportedLocales: ['en', 'zh-CN'] },
+    ));
+    expect(floorWarns(seen.warns)).toHaveLength(1);
+  });
+});