diff --git a/internal/generate-tree.mjs b/internal/generate-tree.mjs
index 7168adced..2b6c9b650 100644
--- a/internal/generate-tree.mjs
+++ b/internal/generate-tree.mjs
@@ -613,6 +613,12 @@ function forgeHtml(o) {
 <head>
   <meta charset="UTF-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <!-- THIS PAGE IS OURS. The only thing that knows a document belongs to the plugin is the page
+       the generator writes, so it says so here. library/i18n reads it before reflecting an RTL
+       locale on <html dir>; nothing else sets it, so a PARTNER page defaults to "not ours" and
+       is never touched. Absence must mean restraint — an embedded plugin flipping a partner's
+       whole <html> because a reader followed a ?lang=ar link is the bug this prevents. -->
+  <script>window.MAP_OWNS_PAGE = true;</script>
   <title>${esc(o.title)}</title>
   <link rel="icon" href="data:,">
   <style>${FORGE_CSS}</style>
@@ -704,6 +710,12 @@ function studioRootHtml(bakedToken, integrity = '') {
 <head>
   <meta charset="UTF-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <!-- THIS PAGE IS OURS. The only thing that knows a document belongs to the plugin is the page
+       the generator writes, so it says so here. library/i18n reads it before reflecting an RTL
+       locale on <html dir>; nothing else sets it, so a PARTNER page defaults to "not ours" and
+       is never touched. Absence must mean restraint — an embedded plugin flipping a partner's
+       whole <html> because a reader followed a ?lang=ar link is the bug this prevents. -->
+  <script>window.MAP_OWNS_PAGE = true;</script>
   <title>${esc(DISPLAY_TITLE)} plugin studio</title>
   <link rel="icon" href="data:,">
 ${bakedToken ? `  <script>window.MAP_TOKEN=${JSON.stringify(bakedToken)};</script>\n` : ''}${DEST_CONFIG.apiBaseUrl ? `  <script>window.MAP_APP_API_URL = ${JSON.stringify(DEST_CONFIG.apiBaseUrl)};</script>\n` : ''}  <style>
@@ -810,6 +822,12 @@ function mapPageHtml(opts) {
 <head>
   <meta charset="UTF-8" />
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+  <!-- THIS PAGE IS OURS. The only thing that knows a document belongs to the plugin is the page
+       the generator writes, so it says so here. library/i18n reads it before reflecting an RTL
+       locale on <html dir>; nothing else sets it, so a PARTNER page defaults to "not ours" and
+       is never touched. Absence must mean restraint — an embedded plugin flipping a partner's
+       whole <html> because a reader followed a ?lang=ar link is the bug this prevents. -->
+  <script>window.MAP_OWNS_PAGE = true;</script>
   <title>${esc(title)}</title>
   <link rel="icon" href="data:,">
   ${peerBlock}
diff --git a/library/i18n/index.js b/library/i18n/index.js
index b2357aa2d..e8009ac40 100644
--- a/library/i18n/index.js
+++ b/library/i18n/index.js
@@ -135,8 +135,22 @@ export function createAppI18n() {
   // Only ever SET it, never clear it: a host page that already declares dir (a
   // WordPress RTL theme) owns that decision, and stomping it to "ltr" for an
   // English map embedded in an Arabic page would break the page around us.
+  // ★ ONLY WHERE WE OWN THE PAGE. This used to run whenever the locale resolved to an RTL
+  // language, which meant an EMBEDDED plugin on a partner's page flipped the PARTNER'S whole
+  // <html> — their headings, their nav, their footer — because a reader followed a ?lang=ar link.
+  // The comment below already worried about the host owning that decision, but it only guarded
+  // against CLEARING dir, never against setting it.
+  //
+  // A GENERATED LEAF owns its document and says so with window.MAP_OWNS_PAGE. Nothing else sets
+  // it, so the DEFAULT IS "not ours" — a partner page that declares nothing is never touched,
+  // which is the safe direction for a flag whose absence must mean restraint.
+  //
+  // The element's OWN direction is not this code's business and never was: ProfileLoader binds
+  // dir on .profile-loader from effectiveLocale (0f6d5049), so the plugin mirrors correctly
+  // whether or not it owns the document. This is only about the page around it.
   try {
-    if (RTL_LOCALES.has(locale) && document?.documentElement) {
+    const ownsPage = typeof window !== 'undefined' && window.MAP_OWNS_PAGE === true
+    if (ownsPage && RTL_LOCALES.has(locale) && document?.documentElement) {
       document.documentElement.dir = 'rtl'
     }
   } catch { /* no document (SSR/tests) — nothing to reflect */ }