Add multi-workspace support to desktop app (#409)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src/features/workspaces/useWorkspaceInit.ts

@@ -0,0 +1,93 @@
+import { useEffect, useState } from "react";
+
+import { applyWorkspace, getDefaultRelayUrl } from "@/shared/api/tauri";
+
+import {
+  loadActiveWorkspaceId,
+  loadWorkspaces,
+  saveActiveWorkspaceId,
+} from "./workspaceStorage";
+
+type WorkspaceInitResult =
+  | { isReady: true; needsSetup: false }
+  | { isReady: false; needsSetup: true; defaultRelayUrl: string }
+  | { isReady: false; needsSetup: false };
+
+/**
+ * Runs once on mount. Loads the active workspace from localStorage
+ * and calls the Tauri backend to apply the workspace config
+ * (keys, relay URL, token).
+ *
+ * Returns a discriminated union — only render the app after the
+ * workspace is applied. When `needsSetup` is true, the caller
+ * should show a first-run welcome screen.
+ */
+export function useWorkspaceInit(): WorkspaceInitResult {
+  const [result, setResult] = useState<WorkspaceInitResult>({
+    isReady: false,
+    needsSetup: false,
+  });
+
+  useEffect(() => {
+    let cancelled = false;
+
+    async function init() {
+      const workspaces = loadWorkspaces();
+
+      if (workspaces.length === 0) {
+        // No workspaces at all — fetch the build default relay URL
+        // so the welcome screen can pre-fill it.
+        try {
+          const defaultRelayUrl = await getDefaultRelayUrl();
+          if (!cancelled) {
+            setResult({ isReady: false, needsSetup: true, defaultRelayUrl });
+          }
+        } catch {
+          // If we can't get the default, fall back to localhost
+          if (!cancelled) {
+            setResult({
+              isReady: false,
+              needsSetup: true,
+              defaultRelayUrl: "ws://localhost:3000",
+            });
+          }
+        }
+        return;
+      }
+
+      // Determine active workspace
+      let activeId = loadActiveWorkspaceId();
+      if (!activeId || !workspaces.find((w) => w.id === activeId)) {
+        activeId = workspaces[0].id;
+        saveActiveWorkspaceId(activeId);
+      }
+
+      const active = workspaces.find((w) => w.id === activeId);
+      if (!active) {
+        if (!cancelled) {
+          setResult({ isReady: true, needsSetup: false });
+        }
+        return;
+      }
+
+      // Apply workspace config to the Tauri backend
+      try {
+        await applyWorkspace(active.relayUrl, active.nsec, active.token);
+      } catch (error) {
+        console.error("Failed to apply workspace to backend:", error);
+      }
+
+      if (!cancelled) {
+        setResult({ isReady: true, needsSetup: false });
+      }
+    }
+
+    void init();
+
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  return result;
+}