diff --git a/src/main.ts b/src/main.ts
index a04d952e..37bd4b84 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -8,6 +8,7 @@ import { CodexTurnDiffView } from "./features/turn-diff/view.obsidian";
 import { CodexPanelRuntime } from "./plugin-runtime";
 import { type CodexPanelSettings, DEFAULT_SETTINGS, getVaultPath, normalizeSettings, settingsMatchStoredSettings } from "./settings/model";
 import { CodexPanelSettingTab } from "./settings/tab.obsidian";
+import { disposeTextareaHeightMirrors } from "./shared/dom/textarea-autogrow.measure";
 
 export default class CodexPanelPlugin extends Plugin {
   settings: CodexPanelSettings = DEFAULT_SETTINGS;
@@ -19,6 +20,7 @@ export default class CodexPanelPlugin extends Plugin {
   });
 
   override async onload(): Promise<void> {
+    disposeTextareaHeightMirrors();
     this.runtime.reset();
     this.vaultPath = getVaultPath(this.app);
     await this.loadSettings();
@@ -77,6 +79,7 @@ export default class CodexPanelPlugin extends Plugin {
 
   override onunload(): void {
     this.runtime.cancelWorkspacePanelReconcile();
+    disposeTextareaHeightMirrors();
   }
 
   async loadSettings(): Promise<void> {
diff --git a/src/shared/dom/textarea-autogrow.measure.ts b/src/shared/dom/textarea-autogrow.measure.ts
index a4f65ab1..381ca24d 100644
--- a/src/shared/dom/textarea-autogrow.measure.ts
+++ b/src/shared/dom/textarea-autogrow.measure.ts
@@ -4,6 +4,7 @@ export interface TextareaHeightOptions {
 }
 
 const textareaHeightMirrors = new WeakMap<Document, HTMLTextAreaElement>();
+const textareaHeightMirrorDocuments = new Set<Document>();
 const TEXTAREA_HEIGHT_MIRROR_CLASS = "codex-panel-textarea-height-mirror";
 
 export function syncTextareaHeight(textarea: HTMLTextAreaElement | null, options: TextareaHeightOptions): void {
@@ -21,6 +22,14 @@ export function syncTextareaHeight(textarea: HTMLTextAreaElement | null, options
   textarea.setCssProps(sizingProps);
 }
 
+export function disposeTextareaHeightMirrors(): void {
+  for (const doc of textareaHeightMirrorDocuments) {
+    for (const mirror of doc.querySelectorAll(`.${TEXTAREA_HEIGHT_MIRROR_CLASS}`)) mirror.remove();
+    textareaHeightMirrors.delete(doc);
+  }
+  textareaHeightMirrorDocuments.clear();
+}
+
 function measureTextareaNaturalScrollHeight(textarea: HTMLTextAreaElement, style: CSSStyleDeclaration): number {
   const mirror = textareaHeightMirror(textarea.ownerDocument);
   mirror.value = textarea.value;
@@ -30,14 +39,17 @@ function measureTextareaNaturalScrollHeight(textarea: HTMLTextAreaElement, style
 
 function textareaHeightMirror(doc: Document): HTMLTextAreaElement {
   const existing = textareaHeightMirrors.get(doc);
-  if (existing) return existing;
-  const mirror = doc.createElement("textarea");
+  if (existing?.isConnected) return existing;
+  const staleMirrors = [...doc.querySelectorAll<HTMLTextAreaElement>(`.${TEXTAREA_HEIGHT_MIRROR_CLASS}`)];
+  const mirror = staleMirrors.shift() ?? doc.createElement("textarea");
+  for (const duplicate of staleMirrors) duplicate.remove();
   mirror.tabIndex = -1;
   mirror.setAttribute("aria-hidden", "true");
   mirror.readOnly = true;
   mirror.addClass(TEXTAREA_HEIGHT_MIRROR_CLASS);
-  doc.body.appendChild(mirror);
+  if (!mirror.isConnected) doc.body.appendChild(mirror);
   textareaHeightMirrors.set(doc, mirror);
+  textareaHeightMirrorDocuments.add(doc);
   return mirror;
 }
 
diff --git a/tests/shared/dom/textarea-autogrow.test.ts b/tests/shared/dom/textarea-autogrow.test.ts
new file mode 100644
index 00000000..bdb75c04
--- /dev/null
+++ b/tests/shared/dom/textarea-autogrow.test.ts
@@ -0,0 +1,43 @@
+// @vitest-environment jsdom
+
+import { afterEach, describe, expect, it } from "vitest";
+
+import { disposeTextareaHeightMirrors, syncTextareaHeight } from "../../../src/shared/dom/textarea-autogrow.measure";
+import { installObsidianDomShims } from "../../support/dom";
+
+installObsidianDomShims();
+
+const MIRROR_SELECTOR = ".codex-panel-textarea-height-mirror";
+
+afterEach(() => {
+  disposeTextareaHeightMirrors();
+  document.body.replaceChildren();
+});
+
+describe("textarea auto-grow measurement", () => {
+  it("adopts one existing mirror and removes reload duplicates", () => {
+    document.body.append(mirror(), mirror());
+    const textarea = document.createElement("textarea");
+    document.body.appendChild(textarea);
+
+    syncTextareaHeight(textarea, { minHeightFallback: 32, maxHeightFallback: 120 });
+
+    expect(document.querySelectorAll(MIRROR_SELECTOR)).toHaveLength(1);
+  });
+
+  it("removes tracked mirrors when the plugin lifecycle ends", () => {
+    const textarea = document.createElement("textarea");
+    document.body.appendChild(textarea);
+    syncTextareaHeight(textarea, { minHeightFallback: 32, maxHeightFallback: 120 });
+
+    disposeTextareaHeightMirrors();
+
+    expect(document.querySelector(MIRROR_SELECTOR)).toBeNull();
+  });
+});
+
+function mirror(): HTMLTextAreaElement {
+  const element = document.createElement("textarea");
+  element.className = MIRROR_SELECTOR.slice(1);
+  return element;
+}