FN-5801: add markdown preview toggle for planning description

Add a markdown/plain toggle to the planning summary description so users can preview formatted content before creating a task.

- add a Description header toggle that switches between editable plain textarea and rendered markdown preview
- render description preview with react-markdown and remark-gfm while preserving expand/collapse layout behavior
- add preview container styles and spacing adjustments for summary form
- add UI interaction test coverage for markdown toggle behavior and rendered heading/bold content
- document the new markdown/plain description toggle in dashboard guide

Files changed:
 docs/dashboard-guide.md                            |  1 +
 packages/dashboard/app/components/PlanningModeModal.css | 18 +++++++-
 packages/dashboard/app/components/PlanningModeModal.tsx | 32 ++++++++++---
 packages/dashboard/app/components/__tests__/PlanningModeModal.ui-interactions.test.tsx | 54 ++++++++++++++++++++++
 4 files changed, 98 insertions(+), 7 deletions(-)

Fusion-Task-Id: FN-5801

Fusion-Task-Lineage: 34972830-7d51-4fcd-bf00-3de8f5aff028

docs/dashboard-guide.md

@@ -109,6 +109,7 @@ Planning Mode now includes branch controls on the summary screen before you crea
   - `Create custom new branch`
 - **Branch name** is required when using `existing` or `custom new` strategies.
 - **Merge target / base branch (optional)** uses a dropdown of existing local branches (with common names like `main`/`master`/`trunk`/`develop` listed first) plus a **Custom…** fallback when you need to type a branch that is not local yet.
+- **Description** supports a `Markdown`/`Plain` toggle in the summary header row: `Plain` keeps the editable textarea, while `Markdown` renders formatted preview (`react-markdown` + GFM) in the same footprint for easier review before task creation.
 
 These values are sent with the Planning Mode create-task request as `branchSelection`, so created tasks persist branch/base-branch settings consistently with other branch-aware task creation flows.
 

packages/dashboard/app/components/PlanningModeModal.css

@@ -606,6 +606,22 @@
   box-shadow: var(--focus-ring);
 }
 
+.planning-description-preview {
+  width: 100%;
+  min-height: calc(var(--space-md) * 7.5);
+  max-height: calc(var(--space-2xl) * 20);
+  padding: var(--space-md);
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: var(--radius-md);
+  color: var(--text);
+  overflow-y: auto;
+}
+
+.planning-description-preview.expanded {
+  min-height: calc(var(--space-md) * 12.5);
+}
+
 .planning-comment-section {
   margin-top: var(--space-lg);
 }
@@ -940,7 +956,7 @@
 .planning-summary-form .form-group {
   display: flex;
   flex-direction: column;
-  gap: 10px;
+  gap: var(--space-sm);
   padding: var(--space-lg);
   background: var(--card);
   border: 1px solid var(--border);

packages/dashboard/app/components/PlanningModeModal.tsx

@@ -1,5 +1,7 @@
 import "./PlanningModeModal.css";
 import { useState, useCallback, useEffect, useRef, useMemo } from "react";
+import ReactMarkdown from "react-markdown";
+import remarkGfm from "remark-gfm";
 import type { Task, PlanningQuestion, PlanningSummary, TaskPriority } from "@fusion/core";
 import { DEFAULT_TASK_PRIORITY, TASK_PRIORITIES, getErrorMessage } from "@fusion/core";
 import {
@@ -2422,6 +2424,7 @@ function SummaryView({
   isLoading,
 }: SummaryViewProps) {
   const [isExpanded, setIsExpanded] = useState(false);
+  const [renderMarkdown, setRenderMarkdown] = useState(false);
   const [selectedDependencies, setSelectedDependencies] = useState<string[]>(
     summary.suggestedDependencies
   );
@@ -2463,6 +2466,17 @@ function SummaryView({
           <div className="form-group">
             <label>
               Description
+              <button
+                type="button"
+                className="planning-expand-btn"
+                aria-pressed={renderMarkdown}
+                aria-label={renderMarkdown ? "Show raw text" : "Show formatted markdown"}
+                title={renderMarkdown ? "Show raw text" : "Show formatted markdown"}
+                data-testid="planning-description-markdown-toggle"
+                onClick={() => setRenderMarkdown(!renderMarkdown)}
+              >
+                {renderMarkdown ? "Plain" : "Markdown"}
+              </button>
               <button
                 type="button"
                 className="planning-expand-btn"
@@ -2471,12 +2485,18 @@ function SummaryView({
                 {isExpanded ? "Collapse" : "Expand"}
               </button>
             </label>
-            <textarea
-              ref={descriptionAutosizeRef}
-              className={`planning-textarea ${isExpanded ? "expanded" : ""}`}
-              value={summary.description}
-              onChange={(e) => onSummaryChange({ ...summary, description: e.target.value })}
-            />
+            {renderMarkdown ? (
+              <div className={`planning-description-preview markdown-body ${isExpanded ? "expanded" : ""}`}>
+                <ReactMarkdown remarkPlugins={[remarkGfm]}>{summary.description}</ReactMarkdown>
+              </div>
+            ) : (
+              <textarea
+                ref={descriptionAutosizeRef}
+                className={`planning-textarea ${isExpanded ? "expanded" : ""}`}
+                value={summary.description}
+                onChange={(e) => onSummaryChange({ ...summary, description: e.target.value })}
+              />
+            )}
           </div>
 
           <div className="task-detail-section">

packages/dashboard/app/components/__tests__/PlanningModeModal.ui-interactions.test.tsx

@@ -728,4 +728,58 @@ describe("PlanningModeModal", () => {
     });
   });
 
+  describe("Summary markdown preview toggle", () => {
+    it("toggles description between plain textarea and formatted markdown preview", async () => {
+      mockConnectPlanningStream.mockImplementationOnce((_sessionId: string, _projectId: string | undefined, handlers: any) => {
+        setTimeout(() => {
+          handlers.onSummary?.({
+            ...mockSummary,
+            description: "## Heading\n\n- item\n\n**bold**",
+          });
+        }, 10);
+
+        return {
+          close: vi.fn(),
+          isConnected: vi.fn().mockReturnValue(true),
+        };
+      });
+
+      const { container } = render(
+        <PlanningModeModal
+          isOpen={true}
+          onClose={mockOnClose}
+          onTaskCreated={mockOnTaskCreated}
+          onTasksCreated={vi.fn()}
+          tasks={mockTasks}
+        />,
+      );
+
+      fireEvent.change(screen.getByPlaceholderText(/e.g., Build a user authentication/), {
+        target: { value: "Build auth system" },
+      });
+      fireEvent.click(screen.getByText("Start Planning"));
+
+      await waitFor(() => {
+        expect(screen.getByText("Planning Complete!")).toBeDefined();
+      });
+
+      expect(container.querySelector(".planning-textarea")).not.toBeNull();
+      expect(container.querySelector(".planning-description-preview")).toBeNull();
+
+      fireEvent.click(screen.getByTestId("planning-description-markdown-toggle"));
+
+      await waitFor(() => {
+        expect(container.querySelector(".planning-description-preview")).not.toBeNull();
+        expect(screen.getByRole("heading", { level: 2, name: "Heading" })).toBeDefined();
+        expect(container.querySelector("strong")?.textContent).toBe("bold");
+      });
+
+      fireEvent.click(screen.getByTestId("planning-description-markdown-toggle"));
+
+      await waitFor(() => {
+        expect(container.querySelector(".planning-textarea")).not.toBeNull();
+      });
+    });
+  });
+
 });