feat(FN-3407): normalize shell host bootstrap

Introduces a canonical shell host context and normalized bootstrap flow for the dashboard, extracting the host initialization logic into a dedicated `shell-host.ts` module with a `ShellHostContext` provider; updates `App.tsx` and `Header` to use the new context, stabilizes related tests, and documen

Fusion-Task-Id: FN-3407

packages/dashboard/app/context/ShellHostContext.tsx

@@ -0,0 +1,44 @@
+import { createContext, useContext, useMemo, type PropsWithChildren } from "react";
+import { getShellHostContext, type ShellHostContext } from "../shell-host";
+
+export interface ShellHostContextValue {
+  host: ShellHostContext;
+  isNativeShell: boolean;
+  kind: ShellHostContext["kind"];
+  mode?: "local" | "remote";
+  connectionId?: string;
+  serverUrl?: string;
+  canOpenConnectionManager?: boolean;
+}
+
+const DEFAULT_HOST: ShellHostContext = { kind: "browser" };
+
+const ShellHostContextReact = createContext<ShellHostContextValue>({
+  host: DEFAULT_HOST,
+  isNativeShell: false,
+  kind: "browser",
+});
+
+function buildValue(host: ShellHostContext): ShellHostContextValue {
+  const isNativeShell = host.kind !== "browser";
+  return {
+    host,
+    isNativeShell,
+    kind: host.kind,
+    ...(isNativeShell ? {
+      mode: host.mode,
+      connectionId: host.connectionId,
+      serverUrl: host.serverUrl,
+      canOpenConnectionManager: host.canOpenConnectionManager,
+    } : {}),
+  };
+}
+
+export function ShellHostProvider({ children }: PropsWithChildren) {
+  const value = useMemo(() => buildValue(getShellHostContext()), []);
+  return <ShellHostContextReact.Provider value={value}>{children}</ShellHostContextReact.Provider>;
+}
+
+export function useShellHostContext(): ShellHostContextValue {
+  return useContext(ShellHostContextReact);
+}

packages/dashboard/app/context/__tests__/ShellHostContext.test.tsx

@@ -0,0 +1,53 @@
+import { render, screen } from "@testing-library/react";
+import { beforeEach, describe, expect, it } from "vitest";
+import { ShellHostProvider, useShellHostContext } from "../ShellHostContext";
+import { __resetShellHostContextForTests } from "../../shell-host";
+
+function Probe() {
+  const value = useShellHostContext();
+  return <pre data-testid="host">{JSON.stringify(value)}</pre>;
+}
+
+describe("ShellHostContext", () => {
+  beforeEach(() => {
+    __resetShellHostContextForTests();
+    window.history.replaceState({}, "", "/");
+    delete (window as Window & Record<string, unknown>).__FUSION_SHELL_HOST_CONTEXT__;
+  });
+
+  it("provides browser defaults", () => {
+    render(
+      <ShellHostProvider>
+        <Probe />
+      </ShellHostProvider>,
+    );
+
+    const value = JSON.parse(screen.getByTestId("host").textContent ?? "{}");
+    expect(value.kind).toBe("browser");
+    expect(value.isNativeShell).toBe(false);
+  });
+
+  it("provides normalized shell fields", () => {
+    (window as Window & Record<string, unknown>).__FUSION_SHELL_HOST_CONTEXT__ = {
+      kind: "desktop-shell",
+      mode: "remote",
+      connectionId: "conn-2",
+      serverUrl: "https://remote.example.com",
+      canOpenConnectionManager: true,
+    };
+
+    render(
+      <ShellHostProvider>
+        <Probe />
+      </ShellHostProvider>,
+    );
+
+    const value = JSON.parse(screen.getByTestId("host").textContent ?? "{}");
+    expect(value.isNativeShell).toBe(true);
+    expect(value.kind).toBe("desktop-shell");
+    expect(value.mode).toBe("remote");
+    expect(value.connectionId).toBe("conn-2");
+    expect(value.serverUrl).toBe("https://remote.example.com");
+    expect(value.canOpenConnectionManager).toBe(true);
+  });
+});