diff --git a/.changeset/send-template-input-org-retired.md b/.changeset/send-template-input-org-retired.md
new file mode 100644
index 0000000000..ff4a3fee23
--- /dev/null
+++ b/.changeset/send-template-input-org-retired.md
@@ -0,0 +1,44 @@
+---
+"@objectstack/spec": minor
+---
+
+feat(spec): retire `SendTemplateInput.org` — the declared org-overlay resolution tenant id nothing ever read (#11832, ADR-0049 enforce-or-remove)
+
+<!-- adr-0087: registered send-template-input-org-retired -->
+
+**BREAKING** accept-set narrowing (compile-time), landing after the v17.0.0 cut
+(the lockstep launch-window convention ships it as `minor`; the migration
+prescription is registered under protocol major 18, where `os migrate meta`
+users will look).
+
+**Removed member:** `SendTemplateInput.org` (`packages/spec/src/contracts/email-service.ts`).
+
+The member was declared as "Tenant id for org-overlay resolution (when
+supported)" and no implementation ever read it: `@objectstack/plugin-email` —
+the only `IEmailService` implementation — resolves templates on
+`(name, locale)` only, so a caller passing `org` got no org-overlay resolution
+and no error; the "(when supported)" hedge was the declaration admitting the
+gap. After #11741 landed `organizationId` beside it, `SendTemplateInput`
+carried two org-shaped keys of which one did nothing — exactly the shape that
+invites an AI author to pick the wrong one.
+
+**FROM → TO:** `sendTemplate({ template, to, org: tenantId, … })` →
+`sendTemplate({ template, to, … })` — delete the `org` key; it never changed
+behaviour, so removing it changes none either. It is **NOT** replaced by
+`organizationId`: that member is the delivery row's tenant stamp
+(`sys_email.organization_id` pass-through, #11741) and opts into no template
+overlay resolution.
+
+**What is refused:** authoring `org` in TypeScript is now an excess-property
+`tsc` error (`SendTemplateInput` is a programmatic contracts interface with no
+Zod surface, so the compiler is the enforcement channel — pinned in
+`email-service.test.ts`). Runtime behaviour is unchanged: nothing ever read
+the member, so a JavaScript caller still passing `org` keeps its exact
+pre-removal outcome (the key is carried inert and ignored).
+
+**What stays:** `SendTemplateInput.organizationId` and
+`SendEmailInput.organizationId` (#11741, Decision 2 of #11303) are untouched,
+semantics included. `RenderTemplateInput` never carried `org`. D3 semantic
+entry `send-template-input-org-retired`; no D2 conversion, because the key
+only ever appeared in a call-time input bag — no metadata seam ever runs on it
+(the `data.engine.update options.upsert` precedent).
diff --git a/packages/spec/src/contracts/email-service.test.ts b/packages/spec/src/contracts/email-service.test.ts
index 0a9c352f5b..d7fbb9b196 100644
--- a/packages/spec/src/contracts/email-service.test.ts
+++ b/packages/spec/src/contracts/email-service.test.ts
@@ -46,3 +46,34 @@ describe('Email Service Contract — organization widening (#11741)', () => {
     expect(widened.organizationId).toBe('org_apex');
   });
 });
+
+/**
+ * #11832 (ADR-0049 enforce-or-remove) — `SendTemplateInput.org` is RETIRED.
+ *
+ * The member declared "Tenant id for org-overlay resolution (when supported)"
+ * and no implementation ever read it: template resolution keys on
+ * `(name, locale)` only, so a caller passing `org` got no overlay resolution
+ * and no error. This is a programmatic contracts interface (nothing parses it
+ * at runtime), so the enforcement channel is the COMPILER: the pin below is a
+ * compile-time assertion that authoring `org` is an excess-property error.
+ * Re-adding the member makes the `@ts-expect-error` directive unused, which is
+ * itself a compile error (TS2578) under `check:test-typecheck` — the pin fails
+ * loudly in both directions.
+ */
+describe('Email Service Contract — SendTemplateInput.org retired (#11832)', () => {
+  it('refuses `org` at compile time (excess property; organizationId is NOT an overlay opt-in)', () => {
+    const input: SendTemplateInput = {
+      template: 'auth.password_reset',
+      to: 'a@b.com',
+      // `org` was removed from SendTemplateInput (#11832); it never resolved
+      // any org overlay. There is no replacement key: `organizationId` is the
+      // delivery row's tenant stamp, not overlay resolution.
+      // @ts-expect-error #11832 — authoring `org` is an excess-property error
+      org: 'org_apex',
+    };
+    // Runtime footnote only — the contract is type-level; the object literal
+    // above still carries the key at runtime, which is exactly the inertness
+    // the removal documents (nothing reads it).
+    expect(input.template).toBe('auth.password_reset');
+  });
+});
diff --git a/packages/spec/src/contracts/email-service.ts b/packages/spec/src/contracts/email-service.ts
index 375d775487..45b2961c6c 100644
--- a/packages/spec/src/contracts/email-service.ts
+++ b/packages/spec/src/contracts/email-service.ts
@@ -181,8 +181,15 @@ export interface SendTemplateInput {
    * behavior). Calendar-day `date` holes are unaffected (tz-naive).
    */
   timezone?: string;
-  /** Tenant id for org-overlay resolution (when supported). */
-  org?: string;
+  // `org` ("Tenant id for org-overlay resolution (when supported)") was REMOVED
+  // 2026-08-25 (#11832, ADR-0049 enforce-or-remove). No implementation ever read
+  // it — template resolution keys on `(name, locale)` only — so the key was
+  // silently inert from the day it was declared; the "(when supported)" hedge
+  // was the declaration admitting it. `organizationId` below is NOT a
+  // replacement: it is the delivery row's tenant stamp (pass-through to
+  // `sys_email.organization_id`, #11741) and does not opt into any overlay
+  // resolution. If org-overlay template rows ever become a measured business
+  // need, that is a new capability with its own ruling — not this key revived.
   /** Envelope sender override (otherwise template.fromOverride → service default). */
   from?: EmailAddress;
   /** Carbon-copy recipients. */
@@ -205,9 +212,10 @@ export interface SendTemplateInput {
    * template send performs, and stamped from there onto
    * `sys_email.organization_id` (#11741). Same contract as
    * {@link SendEmailInput.organizationId}: pass-through only, optional,
-   * absent stays legal. Distinct from {@link SendTemplateInput.org}, which
-   * addresses template org-overlay *resolution*, not the delivery row's
-   * tenant stamp.
+   * absent stays legal. Distinct from the retired `org` member (removed
+   * 2026-08-25, #11832), which declared template org-overlay *resolution*
+   * and was never read — this member stamps the delivery row's tenant and
+   * opts into no overlay resolution.
    */
   organizationId?: string;
 }
diff --git a/packages/spec/src/migrations/entries/semantic/18.send-template-input-org-retired.ts b/packages/spec/src/migrations/entries/semantic/18.send-template-input-org-retired.ts
new file mode 100644
index 0000000000..d71cf6da04
--- /dev/null
+++ b/packages/spec/src/migrations/entries/semantic/18.send-template-input-org-retired.ts
@@ -0,0 +1,36 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+import type { SemanticMigration } from '../../types.js';
+
+export const entry: SemanticMigration = {
+  id: 'send-template-input-org-retired',
+  surface: 'contracts.emailService.sendTemplate input.org',
+  replacement:
+    '(removed — never implemented; delete the key from the call. It is NOT replaced by '
+    + '`organizationId`: that member is the delivery row\'s tenant stamp '
+    + '(`sys_email.organization_id` pass-through, #11741) and opts into no template overlay '
+    + 'resolution)',
+  reason:
+    'ADR-0049 enforce-or-remove (#11832). `SendTemplateInput.org` was declared as "Tenant id '
+    + 'for org-overlay resolution (when supported)" and no implementation ever read it: '
+    + '`@objectstack/plugin-email` — the only IEmailService implementation — resolves templates '
+    + 'on `(name, locale)` only, so a caller passing `org` got no org-overlay resolution and no '
+    + 'error; the "(when supported)" hedge was the declaration admitting the gap. After #11741 '
+    + 'landed `organizationId` beside it, the input carried two org-shaped keys of which one did '
+    + 'nothing — exactly the shape that invites an AI author to pick the wrong one. There is no '
+    + 'behaviour to preserve and nothing stored to rewrite: the key only ever appeared in a '
+    + 'call-time input bag (the `data.engine.update options.upsert` precedent), which is why '
+    + 'this is a D3 semantic entry with no D2 conversion — no metadata seam ever runs on it. '
+    + 'Org-overlay template resolution, if it ever earns a measured business pull, is a new '
+    + 'capability with its own ruling — not this key revived.',
+  acceptanceCriteria:
+    'No caller passes `org` to `IEmailService.sendTemplate()`. The enforcement channel is the '
+    + 'compiler: `SendTemplateInput` is a programmatic contracts interface with no Zod surface, '
+    + 'so authoring `org` is an excess-property `tsc` error (pinned in '
+    + '`packages/spec/src/contracts/email-service.test.ts`). Runtime behaviour is deliberately '
+    + 'UNCHANGED: nothing ever read the member, so removing it removes no behaviour — a '
+    + 'JavaScript caller still passing `org` keeps its exact pre-removal outcome (the key is '
+    + 'carried inert and ignored). Template resolution still keys on `(name, locale)`, and '
+    + '`organizationId` still stamps `sys_email.organization_id` without acquiring any overlay '
+    + 'semantics.',
+};
diff --git a/packages/spec/src/migrations/registry.ts b/packages/spec/src/migrations/registry.ts
index 390c03117e..e372897c15 100644
--- a/packages/spec/src/migrations/registry.ts
+++ b/packages/spec/src/migrations/registry.ts
@@ -6219,6 +6219,38 @@ const step18: MigrationStep = {
         + '`collapsible: true` explicitly — an unset key now defers to the renderer, which does '
         + 'not collapse.',
     },
+    {
+      id: 'send-template-input-org-retired',
+      surface: 'contracts.emailService.sendTemplate input.org',
+      replacement:
+        '(removed — never implemented; delete the key from the call. It is NOT replaced by '
+        + '`organizationId`: that member is the delivery row\'s tenant stamp '
+        + '(`sys_email.organization_id` pass-through, #11741) and opts into no template overlay '
+        + 'resolution)',
+      reason:
+        'ADR-0049 enforce-or-remove (#11832). `SendTemplateInput.org` was declared as "Tenant id '
+        + 'for org-overlay resolution (when supported)" and no implementation ever read it: '
+        + '`@objectstack/plugin-email` — the only IEmailService implementation — resolves templates '
+        + 'on `(name, locale)` only, so a caller passing `org` got no org-overlay resolution and no '
+        + 'error; the "(when supported)" hedge was the declaration admitting the gap. After #11741 '
+        + 'landed `organizationId` beside it, the input carried two org-shaped keys of which one did '
+        + 'nothing — exactly the shape that invites an AI author to pick the wrong one. There is no '
+        + 'behaviour to preserve and nothing stored to rewrite: the key only ever appeared in a '
+        + 'call-time input bag (the `data.engine.update options.upsert` precedent), which is why '
+        + 'this is a D3 semantic entry with no D2 conversion — no metadata seam ever runs on it. '
+        + 'Org-overlay template resolution, if it ever earns a measured business pull, is a new '
+        + 'capability with its own ruling — not this key revived.',
+      acceptanceCriteria:
+        'No caller passes `org` to `IEmailService.sendTemplate()`. The enforcement channel is the '
+        + 'compiler: `SendTemplateInput` is a programmatic contracts interface with no Zod surface, '
+        + 'so authoring `org` is an excess-property `tsc` error (pinned in '
+        + '`packages/spec/src/contracts/email-service.test.ts`). Runtime behaviour is deliberately '
+        + 'UNCHANGED: nothing ever read the member, so removing it removes no behaviour — a '
+        + 'JavaScript caller still passing `org` keeps its exact pre-removal outcome (the key is '
+        + 'carried inert and ignored). Template resolution still keys on `(name, locale)`, and '
+        + '`organizationId` still stamps `sys_email.organization_id` without acquiring any overlay '
+        + 'semantics.',
+    },
     // Registered as D3 SEMANTIC and deliberately NOT as a D2 conversion, on the
     // D2 scope guard (lossless only — the `owd-legacy-read-aliases` / `'full'`
     // precedent): an authored theme has no lossless target. `app.branding` holds