chore(desktop): add navigation boundary lint rule (MUL-4741 Phase 2 prereq)

The tab Coordinator protocol requires that application code never
navigates directly (invariant 1: a Router location change without a
Coordinator token is a protocol error). Enforce it statically:

- renderer app code may not import useNavigate/Navigate from
  react-router-dom nor call router.navigate; src/platform is exempt
- the five known legacy sites (the RFC §8.1 migration checklist,
  cross-validated: the rule fires on exactly those and nothing else)
  carry inline eslint-disable directives tagged MUL-4741 — the Phase 2
  migration removes them one by one, and this rule holding with zero
  disables is the machine check that the migration is complete

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/desktop/eslint.config.mjs

@@ -41,4 +41,39 @@ export default [
       "no-restricted-syntax": "off",
     },
   },
+  // Navigation boundary (MUL-4741): the tab Coordinator must be the only
+  // navigation initiator — a Router location change without a Coordinator
+  // token is a protocol error. Application code must not navigate directly;
+  // it goes through the navigation adapter / Coordinator in src/platform.
+  // Remaining legacy sites carry an inline eslint-disable tagged MUL-4741;
+  // the Phase 2 migration removes them one by one, and this rule holding
+  // with zero disables is the machine check that the migration is complete.
+  {
+    files: ["src/renderer/src/**/*.{ts,tsx}"],
+    ignores: ["src/renderer/src/platform/**", "src/renderer/src/**/*.test.*"],
+    rules: {
+      "no-restricted-imports": [
+        "error",
+        {
+          paths: [
+            {
+              name: "react-router-dom",
+              importNames: ["useNavigate", "Navigate"],
+              message:
+                "Direct navigation from application code breaks the Coordinator protocol (MUL-4741). Use the navigation adapter from src/platform instead.",
+            },
+          ],
+        },
+      ],
+      "no-restricted-syntax": [
+        "error",
+        {
+          selector:
+            "CallExpression[callee.object.name='router'][callee.property.name='navigate']",
+          message:
+            "Direct router.navigate from application code breaks the Coordinator protocol (MUL-4741). Route it through the navigation adapter in src/platform.",
+        },
+      ],
+    },
+  },
 ];

apps/desktop/src/renderer/src/components/route-error-page.tsx

@@ -1,4 +1,5 @@
 import { useMemo } from "react";
+// eslint-disable-next-line no-restricted-imports -- MUL-4741 Phase 2: error recovery moves to the Coordinator; remove with §8.1
 import { useLocation, useNavigate, useRouteError } from "react-router-dom";
 import { AlertTriangle, RotateCw, Send, X } from "lucide-react";
 import { Button } from "@multica/ui/components/ui/button";

apps/desktop/src/renderer/src/components/workspace-route-layout.tsx

@@ -1,4 +1,5 @@
 import { useEffect } from "react";
+// eslint-disable-next-line no-restricted-imports -- MUL-4741 Phase 2: workspace redirect + login bounce move to the Coordinator; remove with §8.1
 import { Outlet, useNavigate, useParams } from "react-router-dom";
 import { useQuery } from "@tanstack/react-query";
 import { WorkspaceSlugProvider, paths } from "@multica/core/paths";

apps/desktop/src/renderer/src/hooks/use-tab-history.ts

@@ -27,12 +27,14 @@ export function useTabHistory() {
   const goBack = useCallback(() => {
     if (!router || historyIndex <= 0) return;
     popDirectionHints.set(router, "back");
+    // eslint-disable-next-line no-restricted-syntax -- MUL-4741 Phase 2: shell back/forward moves to the Coordinator (invariant 1); remove with §8.1
     router.navigate(-1);
   }, [router, historyIndex]);
 
   const goForward = useCallback(() => {
     if (!router || historyIndex >= historyLength - 1) return;
     popDirectionHints.set(router, "forward");
+    // eslint-disable-next-line no-restricted-syntax -- MUL-4741 Phase 2: shell back/forward moves to the Coordinator (invariant 1); remove with §8.1
     router.navigate(1);
   }, [router, historyIndex, historyLength]);
 

apps/desktop/src/renderer/src/routes.tsx

@@ -1,6 +1,7 @@
 import { useEffect } from "react";
 import {
   createMemoryRouter,
+  // eslint-disable-next-line no-restricted-imports -- MUL-4741 Phase 2: index redirect moves to the Coordinator; remove with §8.1
   Navigate,
   Outlet,
   useMatches,