diff --git a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/useEmbeddableChat.ts b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/useEmbeddableChat.ts
index 5420fc92..8d4b18dc 100644
--- a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/useEmbeddableChat.ts
+++ b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/useEmbeddableChat.ts
@@ -51,6 +51,15 @@ type UseEmbeddableChatParams = {
   contextId?: string;
 };
 
+/**
+ * Keys that are held rather than typed.
+ *
+ * A modifier press is not editing, and ending a recall on one would break the ordinary act of holding Shift
+ * between two presses of Up. `Dead` is a pending accent on layouts that compose — also not a keystroke you
+ * have finished making.
+ */
+const MODIFIER_KEYS = new Set(['Shift', 'Control', 'Alt', 'Meta', 'CapsLock', 'Dead']);
+
 export function useEmbeddableChat(params: UseEmbeddableChatParams, onMessageComplete?: () => void) {
   const { initialMessage, defaultInput = '', promptPrefix, cwd, autoSend = false, chat: externalChat } = params;
 
@@ -440,6 +449,18 @@ export function useEmbeddableChat(params: UseEmbeddableChatParams, onMessageComp
     }
     if (ev.key === 'ArrowUp') return recallPrompt(ev, -1);
     if (ev.key === 'ArrowDown') return recallPrompt(ev, 1);
+    /*
+      Anything else ends the recall, and Left/Right are the ones that matter.
+
+      A recalled prompt you have started moving around in is a prompt you have adopted — so the next Up must
+      not walk further back over it, for the same reason Up does not overwrite a fresh draft. Arrowing left
+      into the middle of it is the clearest signal of intent there is, and it types nothing, so a rule based
+      on the text changing would miss it entirely.
+
+      Bare modifiers are excluded: holding Shift to capitalise the next letter is not editing, and treating
+      it as such would end the recall between two presses of Up.
+    */
+    if (!MODIFIER_KEYS.has(ev.key)) history.leave();
     if (ev.key === 'Enter' && !ev.shiftKey) {
       ev.preventDefault();
       // Enter on an EMPTY composer with something queued means "don't wait — say it now". The keystroke
diff --git a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.test.tsx b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.test.tsx
index c01f41ca..435e7c06 100644
--- a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.test.tsx
+++ b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.test.tsx
@@ -103,3 +103,44 @@ describe('what gets remembered', () => {
     expect(current.step(-1, '')).toBe('three');
   });
 });
+
+describe('leaving the history', () => {
+  // The rule this exists for: a recalled prompt you have started editing — or merely arrowed into — is
+  // yours now, and the next Up must not walk further back over it.
+  test('a keystroke after a recall ends it, so Up no longer walks', () => {
+    const { current } = mount();
+    current.record('one');
+    current.record('two');
+
+    expect(current.step(-1, '')).toBe('two');
+    expect(current.isRecalling()).toBe(true);
+
+    current.leave();
+    expect(current.isRecalling()).toBe(false);
+  });
+
+  // The composer's guard is "empty, or recalling". Once we have left, a non-empty box is a draft — so the
+  // two halves together are what stop Up from eating an edited prompt.
+  test('after leaving, the recalled text is treated as a draft', () => {
+    const { current } = mount();
+    current.record('one');
+    current.step(-1, '');
+    current.leave();
+
+    const mayRecall = (value: string) => value.trim() === '' || current.isRecalling();
+    expect(mayRecall('one, edited')).toBe(false);
+    expect(mayRecall('')).toBe(true);
+  });
+
+  // The stashed draft goes with it. Handing an older draft back after you have started editing something
+  // else would paste the wrong text over the right one.
+  test('the stashed draft does not come back later', () => {
+    const { current } = mount();
+    current.record('sent');
+    expect(current.step(-1, 'a draft')).toBe('sent');
+    current.leave();
+    // Entering again stashes what is there NOW, and Down returns that rather than the abandoned draft.
+    expect(current.step(-1, 'something else')).toBe('sent');
+    expect(current.step(1, 'sent')).toBe('something else');
+  });
+});
diff --git a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.ts b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.ts
index 2c0d1acc..c107aa09 100644
--- a/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.ts
+++ b/src/workspaces/officerdev/src/apps/Chat/EmbeddableChat/usePromptHistory.ts
@@ -34,6 +34,17 @@ export type PromptHistory = {
    * then refuse. This is the difference between "there is text" and "there is text of yours".
    */
   isRecalling: () => boolean;
+  /**
+   * Stop being in the history — the recalled text is now the person's own draft.
+   *
+   * Called on any keystroke that is not Up or Down. The moment you edit a recalled prompt, or even just
+   * move the caret through it with Left, you have adopted it: pressing Up after that would throw away
+   * something you were working on, which is the same fault as recalling over a fresh draft.
+   *
+   * The stashed draft goes too. It belonged to the composing session this leaves, and handing it back after
+   * you have started editing something else would paste an older draft over a newer one.
+   */
+  leave: () => void;
 };
 
 export function usePromptHistory(): PromptHistory {
@@ -98,5 +109,10 @@ export function usePromptHistory(): PromptHistory {
 
   const isRecalling = useCallback(() => indexRef.current !== null, []);
 
-  return { record, step, isRecalling };
+  const leave = useCallback(() => {
+    indexRef.current = null;
+    draftRef.current = '';
+  }, []);
+
+  return { record, step, isRecalling, leave };
 }