fix: Windows CI C++17 flag for ICU 78+ and add CSP validation tests

- Set CXXFLAGS=/std:c++17 on Windows CI (ICU 78+ requires C++17 features
  like nested-namespace-definition and auto in non-type template params)
- Add Vitest tests validating tauri.conf.json CSP configuration to prevent
  regressions (dangerousDisableAssetCspModification, style-src, connect-src,
  font-src directives)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build-desktop.yml

@@ -78,8 +78,8 @@ jobs:
           echo "VCPKGRS_TRIPLET=x64-windows-static-release" >> $GITHUB_ENV
           echo "VCPKG_DEFAULT_HOST_TRIPLET=x64-windows-static-release" >> $GITHUB_ENV
           echo "RUSTFLAGS=-Ctarget-feature=+crt-static" >> $GITHUB_ENV
-          # Override macOS-specific flags from .cargo/config.toml
-          echo "CXXFLAGS=" >> $GITHUB_ENV
+          # Override macOS-specific paths from .cargo/config.toml; ICU 78+ requires C++17
+          echo "CXXFLAGS=/std:c++17" >> $GITHUB_ENV
           echo "CFLAGS=" >> $GITHUB_ENV
 
       - name: Setup Apple code signing

apps/desktop/src/__tests__/tauri-conf-csp.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "fs";
+import { resolve } from "path";
+
+/**
+ * Validates tauri.conf.json CSP (Content Security Policy) configuration.
+ *
+ * Background: Tauri 2 injects nonces into CSP directives at build time.
+ * Per CSP spec, when a nonce is present, 'unsafe-inline' is ignored by the browser.
+ * This means dynamically injected <style> tags (e.g., from CodeMirror's style-mod)
+ * get blocked in production builds, causing invisible editor text.
+ *
+ * The fix: `dangerousDisableAssetCspModification` prevents Tauri from adding nonces,
+ * so 'unsafe-inline' remains effective for runtime style injection.
+ */
+describe("tauri.conf.json CSP configuration", () => {
+  const confPath = resolve(__dirname, "../../src-tauri/tauri.conf.json");
+  const conf = JSON.parse(readFileSync(confPath, "utf-8"));
+  const security = conf.app?.security;
+  const csp = security?.csp ?? "";
+
+  it("should have dangerousDisableAssetCspModification enabled so runtime style injection works", () => {
+    expect(security?.dangerousDisableAssetCspModification).toBe(true);
+  });
+
+  it("should include 'unsafe-inline' in style-src for CodeMirror dynamic styles", () => {
+    const styleSrc = csp.match(/style-src\s+([^;]+)/)?.[1] ?? "";
+    expect(styleSrc).toContain("'unsafe-inline'");
+  });
+
+  it("should include ipc: in connect-src for Tauri IPC in production", () => {
+    const connectSrc = csp.match(/connect-src\s+([^;]+)/)?.[1] ?? "";
+    expect(connectSrc).toContain("ipc:");
+  });
+
+  it("should include data: in font-src for base64-encoded fonts", () => {
+    const fontSrc = csp.match(/font-src\s+([^;]+)/)?.[1] ?? "";
+    expect(fontSrc).toContain("data:");
+  });
+});