diff --git a/packages/dashboard/app/components/WorkflowNodeEditor.tsx b/packages/dashboard/app/components/WorkflowNodeEditor.tsx
index c975265a58..77d03c33cb 100644
--- a/packages/dashboard/app/components/WorkflowNodeEditor.tsx
+++ b/packages/dashboard/app/components/WorkflowNodeEditor.tsx
@@ -14,6 +14,7 @@ import {
   type Node as FlowNode,
   type Edge as FlowEdge,
 } from "@xyflow/react";
+import { createPortal } from "react-dom";
 import { useTranslation } from "react-i18next";
 import { X, Plus, Trash2, Save, MessageSquare, Terminal, Shield, GitMerge, Loader2, HelpCircle, PauseCircle, Split, Merge, Repeat, ClipboardCheck, ListChecks, Code2, Bell, LayoutGrid, Workflow, Download, Upload, ChevronDown, ChevronRight, ChevronLeft, Library, Sparkles, Maximize2, Minimize2 } from "lucide-react";
 import type { WorkflowDefinition, WorkflowIrColumn, TraitViolation, WorkflowStepTemplate } from "@fusion/core";
@@ -2123,9 +2124,42 @@ function InnerEditor({
   }, [overrideColumnBinding, agents.length, projectId, addToast]);
 
   const overlayProps = useOverlayDismiss(requestClose);
+  const promptFullscreenOverlay =
+    isPromptExpanded && (selectedNode?.data.kind === "prompt" || selectedNode?.data.kind === "gate")
+      ? createPortal(
+          <div
+            className="wf-prompt-editor wf-prompt-editor--fullscreen"
+            onKeyDown={handlePromptFullscreenKeyDown}
+          >
+            <div className="wf-prompt-fullscreen-header">
+              <span>{t("workflowEditor.editingPrompt", "Editing Prompt")}</span>
+              <button
+                type="button"
+                className="btn btn-sm wf-prompt-expand-btn"
+                onClick={handleTogglePromptExpand}
+                aria-label={t("workflowEditor.collapsePrompt", "Collapse prompt editor")}
+                title={t("workflowEditor.collapsePrompt", "Collapse prompt editor")}
+              >
+                <Minimize2 size={14} />
+              </button>
+            </div>
+            <label className="wf-field">
+              <span>Prompt</span>
+              <textarea
+                rows={undefined}
+                value={selectedNodePromptValue}
+                onChange={(e) => updateSelectedData({ config: { prompt: e.target.value } })}
+                autoFocus
+              />
+            </label>
+          </div>,
+          document.body,
+        )
+      : null;
 
   return (
-    <div className="modal-overlay open wf-editor-overlay" {...overlayProps}>
+    <>
+      <div className="modal-overlay open wf-editor-overlay" {...overlayProps}>
       <div
         className="modal wf-editor-modal"
         ref={modalRef}
@@ -3144,43 +3178,24 @@ function InnerEditor({
               </label>
 
               {selectedNode.data.kind === "prompt" || selectedNode.data.kind === "gate" ? (
-                <div
-                  className={`wf-prompt-editor${isPromptExpanded ? " wf-prompt-editor--fullscreen" : ""}`}
-                  onKeyDown={handlePromptFullscreenKeyDown}
-                >
-                  {isPromptExpanded && (
-                    <div className="wf-prompt-fullscreen-header">
-                      <span>{t("workflowEditor.editingPrompt", "Editing Prompt")}</span>
-                      <button
-                        type="button"
-                        className="btn btn-sm wf-prompt-expand-btn"
-                        onClick={handleTogglePromptExpand}
-                        aria-label={t("workflowEditor.collapsePrompt", "Collapse prompt editor")}
-                        title={t("workflowEditor.collapsePrompt", "Collapse prompt editor")}
-                      >
-                        <Minimize2 size={14} />
-                      </button>
-                    </div>
-                  )}
+                <div className="wf-prompt-editor">
                   <label className="wf-field">
                     <span>Prompt</span>
                     <textarea
-                      rows={isPromptExpanded ? undefined : 5}
+                      rows={5}
                       value={selectedNodePromptValue}
                       onChange={(e) => updateSelectedData({ config: { prompt: e.target.value } })}
                     />
                   </label>
-                  {!isPromptExpanded && (
-                    <button
-                      type="button"
-                      className="btn btn-sm wf-prompt-expand-btn wf-prompt-expand-btn--inline"
-                      onClick={handleTogglePromptExpand}
-                      aria-label={t("workflowEditor.expandPrompt", "Expand prompt editor")}
-                      title={t("workflowEditor.expandPrompt", "Expand prompt editor")}
-                    >
-                      <Maximize2 size={14} />
-                    </button>
-                  )}
+                  <button
+                    type="button"
+                    className="btn btn-sm wf-prompt-expand-btn wf-prompt-expand-btn--inline"
+                    onClick={handleTogglePromptExpand}
+                    aria-label={t("workflowEditor.expandPrompt", "Expand prompt editor")}
+                    title={t("workflowEditor.expandPrompt", "Expand prompt editor")}
+                  >
+                    <Maximize2 size={14} />
+                  </button>
                 </div>
               ) : null}
 
@@ -4177,7 +4192,9 @@ function InnerEditor({
           />
         )}
       </div>
-    </div>
+      </div>
+      {promptFullscreenOverlay}
+    </>
   );
 }
 
diff --git a/packages/dashboard/app/components/__tests__/WorkflowNodeEditor.test.tsx b/packages/dashboard/app/components/__tests__/WorkflowNodeEditor.test.tsx
index 4c15e741ff..620bea75e4 100644
--- a/packages/dashboard/app/components/__tests__/WorkflowNodeEditor.test.tsx
+++ b/packages/dashboard/app/components/__tests__/WorkflowNodeEditor.test.tsx
@@ -83,6 +83,16 @@ import { WorkflowNodeEditor } from "../WorkflowNodeEditor";
 import { ConfirmDialogProvider } from "../../hooks/useConfirm";
 import { MOBILE_MEDIA_QUERY } from "../../hooks/useViewportMode";
 
+function getPromptFullscreenOverlay() {
+  return document.body.querySelector(".wf-prompt-editor--fullscreen") as HTMLElement | null;
+}
+
+function getPromptFullscreenTextarea() {
+  const overlay = getPromptFullscreenOverlay();
+  expect(overlay).not.toBeNull();
+  return within(overlay!).getByLabelText("Prompt") as HTMLTextAreaElement;
+}
+
 function mockWorkflowEditorViewport(mode: "desktop" | "mobile" | "tablet" = "desktop") {
   Object.defineProperty(window, "matchMedia", {
     writable: true,
@@ -528,19 +538,22 @@ describe("WorkflowNodeEditor", () => {
     const expand = await screen.findByRole("button", { name: "Expand prompt editor" });
     expect(expand).toBeInTheDocument();
 
-    const promptEditor = expand.closest(".wf-prompt-editor");
-    expect(promptEditor).not.toBeNull();
-    expect(promptEditor).not.toHaveClass("wf-prompt-editor--fullscreen");
+    const inlinePromptEditor = expand.closest(".wf-prompt-editor");
+    expect(inlinePromptEditor).not.toBeNull();
+    expect(inlinePromptEditor).not.toHaveClass("wf-prompt-editor--fullscreen");
+    expect(getPromptFullscreenOverlay()).toBeNull();
 
     fireEvent.click(expand);
 
-    expect(promptEditor).toHaveClass("wf-prompt-editor--fullscreen");
-    expect(screen.getByRole("button", { name: "Collapse prompt editor" })).toBeVisible();
-    expect(screen.getByLabelText("Prompt")).not.toHaveAttribute("rows");
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+    expect(inlinePromptEditor).not.toHaveClass("wf-prompt-editor--fullscreen");
+    expect(within(fullscreenPromptEditor!).getByRole("button", { name: "Collapse prompt editor" })).toBeVisible();
+    expect(getPromptFullscreenTextarea()).not.toHaveAttribute("rows");
 
-    fireEvent.click(screen.getByRole("button", { name: "Collapse prompt editor" }));
+    fireEvent.click(within(fullscreenPromptEditor!).getByRole("button", { name: "Collapse prompt editor" }));
 
-    expect(promptEditor).not.toHaveClass("wf-prompt-editor--fullscreen");
+    expect(getPromptFullscreenOverlay()).toBeNull();
     expect(screen.getByRole("button", { name: "Expand prompt editor" })).toBeInTheDocument();
   });
 
@@ -553,13 +566,12 @@ describe("WorkflowNodeEditor", () => {
     fireEvent.click(await screen.findByTestId("wf-node-prompt"));
     fireEvent.click(await screen.findByRole("button", { name: "Expand prompt editor" }));
 
-    const promptEditor = screen.getByRole("button", { name: "Collapse prompt editor" }).closest(".wf-prompt-editor");
-    expect(promptEditor).not.toBeNull();
-    expect(promptEditor).toHaveClass("wf-prompt-editor--fullscreen");
+    const promptEditor = getPromptFullscreenOverlay();
+    expect(promptEditor).toBeInTheDocument();
 
     fireEvent.keyDown(promptEditor!, { key: "Escape" });
 
-    expect(promptEditor).not.toHaveClass("wf-prompt-editor--fullscreen");
+    expect(getPromptFullscreenOverlay()).toBeNull();
     expect(screen.getByRole("button", { name: "Expand prompt editor" })).toBeInTheDocument();
   });
 
@@ -577,6 +589,97 @@ describe("WorkflowNodeEditor", () => {
     expect(within(inspector).getByRole("button", { name: "Expand prompt editor" })).toBeInTheDocument();
   });
 
+  it("opens the fullscreen prompt editor from the mobile prompt inspector", async () => {
+    mockWorkflowEditorViewport("mobile");
+    vi.mocked(fetchWorkflows).mockResolvedValue([v2Def()]);
+
+    render(<WorkflowNodeEditor isOpen onClose={() => {}} addToast={() => {}} />);
+
+    fireEvent.click(await screen.findByRole("button", { name: "Custom" }));
+    fireEvent.click(await screen.findByTestId("wf-node-prompt"));
+
+    const inspector = await screen.findByTestId("wf-node-inspector");
+    fireEvent.click(within(inspector).getByRole("button", { name: "Expand prompt editor" }));
+
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+    expect(within(fullscreenPromptEditor!).getByRole("button", { name: "Collapse prompt editor" })).toBeVisible();
+    expect(getPromptFullscreenTextarea()).toHaveFocus();
+  });
+
+  it("closes the fullscreen prompt editor with the mobile collapse button", async () => {
+    mockWorkflowEditorViewport("mobile");
+    vi.mocked(fetchWorkflows).mockResolvedValue([v2Def()]);
+
+    render(<WorkflowNodeEditor isOpen onClose={() => {}} addToast={() => {}} />);
+
+    fireEvent.click(await screen.findByRole("button", { name: "Custom" }));
+    fireEvent.click(await screen.findByTestId("wf-node-prompt"));
+    fireEvent.click(await screen.findByRole("button", { name: "Expand prompt editor" }));
+
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+
+    fireEvent.click(within(fullscreenPromptEditor!).getByRole("button", { name: "Collapse prompt editor" }));
+
+    expect(getPromptFullscreenOverlay()).toBeNull();
+  });
+
+  it("closes the fullscreen prompt editor with Escape on mobile", async () => {
+    mockWorkflowEditorViewport("mobile");
+    vi.mocked(fetchWorkflows).mockResolvedValue([v2Def()]);
+
+    render(<WorkflowNodeEditor isOpen onClose={() => {}} addToast={() => {}} />);
+
+    fireEvent.click(await screen.findByRole("button", { name: "Custom" }));
+    fireEvent.click(await screen.findByTestId("wf-node-prompt"));
+    fireEvent.click(await screen.findByRole("button", { name: "Expand prompt editor" }));
+
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+
+    fireEvent.keyDown(fullscreenPromptEditor!, { key: "Escape" });
+
+    expect(getPromptFullscreenOverlay()).toBeNull();
+  });
+
+  it("persists mobile fullscreen prompt edits back to the inline textarea", async () => {
+    mockWorkflowEditorViewport("mobile");
+    vi.mocked(fetchWorkflows).mockResolvedValue([v2Def()]);
+
+    render(<WorkflowNodeEditor isOpen onClose={() => {}} addToast={() => {}} />);
+
+    fireEvent.click(await screen.findByRole("button", { name: "Custom" }));
+    fireEvent.click(await screen.findByTestId("wf-node-prompt"));
+    fireEvent.click(await screen.findByRole("button", { name: "Expand prompt editor" }));
+
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+
+    fireEvent.change(getPromptFullscreenTextarea(), { target: { value: "mobile edit" } });
+    fireEvent.click(within(fullscreenPromptEditor!).getByRole("button", { name: "Collapse prompt editor" }));
+
+    const inspector = await screen.findByTestId("wf-node-inspector");
+    expect(within(inspector).getByLabelText("Prompt")).toHaveValue("mobile edit");
+  });
+
+  it("opens the fullscreen prompt editor for empty mobile gate prompts", async () => {
+    mockWorkflowEditorViewport("mobile");
+    vi.mocked(fetchWorkflows).mockResolvedValue([def()]);
+
+    render(<WorkflowNodeEditor isOpen onClose={() => {}} addToast={() => {}} />);
+
+    fireEvent.click(await screen.findByRole("button", { name: "QA" }));
+    fireEvent.click(await screen.findByTestId("wf-node-gate"));
+
+    const inspector = await screen.findByTestId("wf-node-inspector");
+    fireEvent.click(within(inspector).getByRole("button", { name: "Expand prompt editor" }));
+
+    const fullscreenPromptEditor = getPromptFullscreenOverlay();
+    expect(fullscreenPromptEditor).toBeInTheDocument();
+    expect(within(fullscreenPromptEditor!).getByLabelText("Prompt")).toHaveValue("");
+  });
+
   it("does not show the prompt expand button for non-prompt nodes", async () => {
     vi.mocked(fetchWorkflows).mockResolvedValue([scriptDef()]);