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/__tests__/shell-host.test.ts

@@ -0,0 +1,65 @@
+import { describe, expect, it, beforeEach } from "vitest";
+import {
+  __resetShellHostContextForTests,
+  bootstrapShellHostContext,
+  detectShellHostContext,
+} from "../shell-host";
+
+describe("shell-host", () => {
+  beforeEach(() => {
+    __resetShellHostContextForTests();
+    window.history.replaceState({}, "", "/");
+    delete (window as Window & { fusionAPI?: unknown }).fusionAPI;
+    delete (window as Window & Record<string, unknown>).__FUSION_SHELL_HOST_CONTEXT__;
+  });
+
+  it("falls back to browser when no shell signals are present", () => {
+    expect(detectShellHostContext()).toEqual({ kind: "browser" });
+  });
+
+  it("detects desktop shell via fusionAPI fallback", () => {
+    (window as Window & { fusionAPI?: unknown }).fusionAPI = {};
+    expect(detectShellHostContext()).toEqual({ kind: "desktop-shell" });
+  });
+
+  it("normalizes explicit global handoff", () => {
+    (window as Window & Record<string, unknown>).__FUSION_SHELL_HOST_CONTEXT__ = {
+      kind: "mobile-shell",
+      mode: "remote",
+      connectionId: "conn-1",
+      serverUrl: "https://fusion.example.com/",
+      canOpenConnectionManager: true,
+    };
+
+    expect(detectShellHostContext()).toEqual({
+      kind: "mobile-shell",
+      mode: "remote",
+      connectionId: "conn-1",
+      serverUrl: "https://fusion.example.com",
+      canOpenConnectionManager: true,
+    });
+  });
+
+  it("maps FN-3406 legacy query params into canonical contract", () => {
+    window.history.replaceState({}, "", "/?shellKind=desktop&shellMode=remote&profileId=p1&serverBaseUrl=https%3A%2F%2Fremote.example.com%2F&shellCanOpenConnectionManager=1");
+
+    expect(detectShellHostContext()).toEqual({
+      kind: "desktop-shell",
+      mode: "remote",
+      connectionId: "p1",
+      serverUrl: "https://remote.example.com",
+      canOpenConnectionManager: true,
+    });
+  });
+
+  it("handles malformed handoff values without crashing", () => {
+    window.history.replaceState({}, "", "/?shellKind=mobile&shellMode=invalid&serverBaseUrl=notaurl");
+    expect(detectShellHostContext()).toEqual({ kind: "mobile-shell" });
+  });
+
+  it("strips shell launch params from URL at bootstrap", () => {
+    window.history.replaceState({}, "", "/dashboard?view=board&shellKind=desktop&shellMode=remote&profileId=p1#section");
+    bootstrapShellHostContext();
+    expect(window.location.pathname + window.location.search + window.location.hash).toBe("/dashboard?view=board#section");
+  });
+});