diff --git a/ui/src/pages/AgentDetail.instructions.test.tsx b/ui/src/pages/AgentDetail.instructions.test.tsx
index a255227770..3f0dbfbf13 100644
--- a/ui/src/pages/AgentDetail.instructions.test.tsx
+++ b/ui/src/pages/AgentDetail.instructions.test.tsx
@@ -62,6 +62,7 @@ vi.mock("../components/MarkdownEditor", () => ({
   }) => {
     markdownEditorRenderMock({
       value,
+      onChange,
       contentClassName,
       hasImageUploadHandler: Boolean(imageUploadHandler),
     });
@@ -301,6 +302,7 @@ describe("PromptsTab instruction editor", () => {
     }));
 
     await act(async () => {
+      editor.dispatchEvent(new MouseEvent("pointerdown", { bubbles: true }));
       setNativeValue(editor, "# Updated");
     });
     await waitFor(() => {
@@ -321,6 +323,75 @@ describe("PromptsTab instruction editor", () => {
     });
   });
 
+  it("ignores rich-editor mount normalization until the user interacts", async () => {
+    const summary = makeSummary("AGENTS.md", "AGENTS.md");
+    const onDirtyChange = vi.fn();
+    await renderPromptsTab(
+      makeBundle("AGENTS.md", [summary]),
+      { "AGENTS.md": makeDetail(summary, "# Current") },
+      { onDirtyChange },
+    );
+
+    const editorProps = await waitFor(() => {
+      const latest = markdownEditorRenderMock.mock.calls.at(-1)?.[0] as
+        | { onChange?: (value: string) => void }
+        | undefined;
+      expect(latest?.onChange).toEqual(expect.any(Function));
+      return latest!;
+    });
+
+    await act(async () => {
+      editorProps.onChange?.("# Current\n");
+    });
+    await flushReact();
+
+    expect(onDirtyChange).not.toHaveBeenCalledWith(true);
+    expect(saveAction).toBeNull();
+    expect(mockAgentsApi.saveInstructionsFile).not.toHaveBeenCalled();
+  });
+
+  it("releases dirty state and save controls when the instructions tab unmounts", async () => {
+    const summary = makeSummary("AGENTS.md", "AGENTS.md");
+    const onDirtyChange = vi.fn();
+    const onSavingChange = vi.fn();
+    let cancelAction: (() => void) | null = null;
+    await renderPromptsTab(
+      makeBundle("AGENTS.md", [summary]),
+      { "AGENTS.md": makeDetail(summary, "# Current") },
+      {
+        onDirtyChange,
+        onSavingChange,
+        onSaveActionChange: (next) => { saveAction = next; },
+        onCancelActionChange: (next) => { cancelAction = next; },
+      },
+    );
+
+    const editor = await waitFor(() => {
+      const candidate = container.querySelector<HTMLTextAreaElement>('[data-testid="markdown-editor"]');
+      expect(candidate).not.toBeNull();
+      return candidate!;
+    });
+    await act(async () => {
+      editor.dispatchEvent(new MouseEvent("pointerdown", { bubbles: true }));
+      setNativeValue(editor, "# Updated");
+    });
+    await waitFor(() => {
+      expect(onDirtyChange).toHaveBeenLastCalledWith(true);
+      expect(saveAction).toEqual(expect.any(Function));
+      expect(cancelAction).toEqual(expect.any(Function));
+    });
+
+    await act(async () => {
+      root?.unmount();
+    });
+    root = null;
+
+    expect(onDirtyChange).toHaveBeenLastCalledWith(false);
+    expect(onSavingChange).toHaveBeenLastCalledWith(false);
+    expect(saveAction).toBeNull();
+    expect(cancelAction).toBeNull();
+  });
+
   it("uses the Markdown editor for pending new .md files before server metadata exists", async () => {
     const summary = makeSummary("settings.json", "settings.json", {
       language: "json",
diff --git a/ui/src/pages/AgentDetail.tsx b/ui/src/pages/AgentDetail.tsx
index 962969cb2d..213016d4ee 100644
--- a/ui/src/pages/AgentDetail.tsx
+++ b/ui/src/pages/AgentDetail.tsx
@@ -2303,7 +2303,7 @@ export function PromptsTab({
   const queryClient = useQueryClient();
   const { selectedCompanyId } = useCompany();
   const { isMobile } = useSidebar();
-  const [selectedFile, setSelectedFile] = useState<string>("AGENTS.md");
+  const [selectedFile, setSelectedFileState] = useState<string>("AGENTS.md");
   const [showFilePanel, setShowFilePanel] = useState(false);
   const [draft, setDraft] = useState<string | null>(null);
   const [bundleDraft, setBundleDraft] = useState<{
@@ -2325,8 +2325,20 @@ export function PromptsTab({
     entryFile: string;
     selectedFile: string;
   } | null>(null);
+  // MDXEditor can normalize markdown and emit onChange while it mounts. Only
+  // treat editor output as a draft after a real interaction so merely opening
+  // an instructions file cannot mark the agent dirty.
+  const editorInteractedRef = useRef(false);
+  const markEditorInteracted = useCallback(() => {
+    editorInteractedRef.current = true;
+  }, []);
+  const setSelectedFile = useCallback((filePath: string) => {
+    editorInteractedRef.current = false;
+    setSelectedFileState(filePath);
+  }, []);
 
   useEffect(() => {
+    editorInteractedRef.current = false;
     setSelectedFile("AGENTS.md");
     setShowFilePanel(false);
     setDraft(null);
@@ -2393,7 +2405,10 @@ export function PromptsTab({
       entryFile?: string;
       clearLegacyPromptTemplate?: boolean;
     }) => agentsApi.updateInstructionsBundle(agent.id, data, companyId),
-    onMutate: () => setAwaitingRefresh(true),
+    onMutate: () => {
+      editorInteractedRef.current = false;
+      setAwaitingRefresh(true);
+    },
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: queryKeys.agents.instructionsBundle(agent.id) });
       queryClient.invalidateQueries({ queryKey: queryKeys.agents.detail(agent.id) });
@@ -2405,7 +2420,10 @@ export function PromptsTab({
   const saveFile = useMutation({
     mutationFn: (data: { path: string; content: string; clearLegacyPromptTemplate?: boolean }) =>
       agentsApi.saveInstructionsFile(agent.id, data, companyId),
-    onMutate: () => setAwaitingRefresh(true),
+    onMutate: () => {
+      editorInteractedRef.current = false;
+      setAwaitingRefresh(true);
+    },
     onSuccess: (_, variables) => {
       setPendingFiles((prev) => prev.filter((f) => f !== variables.path));
       queryClient.invalidateQueries({ queryKey: queryKeys.agents.instructionsBundle(agent.id) });
@@ -2418,7 +2436,10 @@ export function PromptsTab({
 
   const deleteFile = useMutation({
     mutationFn: (relativePath: string) => agentsApi.deleteInstructionsFile(agent.id, relativePath, companyId),
-    onMutate: () => setAwaitingRefresh(true),
+    onMutate: () => {
+      editorInteractedRef.current = false;
+      setAwaitingRefresh(true);
+    },
     onSuccess: (_, relativePath) => {
       queryClient.invalidateQueries({ queryKey: queryKeys.agents.instructionsBundle(agent.id) });
       queryClient.removeQueries({ queryKey: queryKeys.agents.instructionsFile(agent.id, relativePath) });
@@ -2545,6 +2566,13 @@ export function PromptsTab({
   useEffect(() => { onSavingChange(isSaving); }, [onSavingChange, isSaving]);
   useEffect(() => { onDirtyChange(isDirty); }, [onDirtyChange, isDirty]);
 
+  useEffect(() => () => {
+    onSaveActionChange(null);
+    onCancelActionChange(null);
+    onDirtyChange(false);
+    onSavingChange(false);
+  }, [onCancelActionChange, onDirtyChange, onSaveActionChange, onSavingChange]);
+
   useEffect(() => {
     onSaveActionChange(isDirty ? () => {
       const save = async () => {
@@ -3005,19 +3033,31 @@ export function PromptsTab({
           {selectedFileExists && fileLoading && !selectedFileDetail ? (
             <PromptEditorSkeleton />
           ) : useMarkdownEditor ? (
-            <MarkdownEditor
-              key={selectedOrEntryFile}
-              value={displayValue}
-              onChange={(value) => setDraft(value ?? "")}
-              placeholder="# Agent instructions"
-              className="min-w-0 overflow-hidden"
-              contentClassName="min-h-(--sz-420px) max-w-full break-words text-sm leading-7"
-              imageUploadHandler={async (file) => {
-                const namespace = `agents/${agent.id}/instructions/${selectedOrEntryFile.replaceAll("/", "-")}`;
-                const asset = await uploadMarkdownImage.mutateAsync({ file, namespace });
-                return asset.contentPath;
-              }}
-            />
+            <div
+              onBeforeInputCapture={markEditorInteracted}
+              onDropCapture={markEditorInteracted}
+              onInput={markEditorInteracted}
+              onKeyDownCapture={markEditorInteracted}
+              onPasteCapture={markEditorInteracted}
+              onPointerDownCapture={markEditorInteracted}
+            >
+              <MarkdownEditor
+                key={selectedOrEntryFile}
+                value={displayValue}
+                onChange={(value) => {
+                  if (!editorInteractedRef.current) return;
+                  setDraft(value ?? "");
+                }}
+                placeholder="# Agent instructions"
+                className="min-w-0 overflow-hidden"
+                contentClassName="min-h-(--sz-420px) max-w-full break-words text-sm leading-7"
+                imageUploadHandler={async (file) => {
+                  const namespace = `agents/${agent.id}/instructions/${selectedOrEntryFile.replaceAll("/", "-")}`;
+                  const asset = await uploadMarkdownImage.mutateAsync({ file, namespace });
+                  return asset.contentPath;
+                }}
+              />
+            </div>
           ) : (
             <textarea
               value={displayValue}