diff --git a/apps/desktop/electron/main/csp.test.ts b/apps/desktop/electron/main/csp.test.ts
new file mode 100644
index 0000000..d87929d
--- /dev/null
+++ b/apps/desktop/electron/main/csp.test.ts
@@ -0,0 +1,62 @@
+import { createHash } from 'node:crypto'
+import { describe, expect, it } from 'vitest'
+import { contentSecurityPolicy, inlineScriptHashes } from './csp.js'
+
+const sha256 = (body: string) => `'sha256-${createHash('sha256').update(body, 'utf8').digest('base64')}'`
+
+describe('inlineScriptHashes', () => {
+  it('hashes the Flight payload scripts a Next export ships', () => {
+    // The bug this exists to prevent: under script-src 'self' these are refused,
+    // React boots with no payload, and the window is blank.
+    const body = '(self.__next_f=self.__next_f||[]).push([0])'
+    expect(inlineScriptHashes(`<html><body><script>${body}</script></body></html>`)).toEqual([sha256(body)])
+  })
+
+  it('ignores scripts that load from a src', () => {
+    const html = '<script src="/_next/static/chunks/main.js"></script>'
+    expect(inlineScriptHashes(html)).toEqual([])
+  })
+
+  it('still hashes an inline script that carries other attributes', () => {
+    // An attribute Next adds later must not silently drop a script out of the policy.
+    const html = '<script type="text/javascript" defer>alert(1)</script>'
+    expect(inlineScriptHashes(html)).toEqual([sha256('alert(1)')])
+  })
+
+  it('does not mistake a src on a later tag for one on this tag', () => {
+    const html = '<script>a()</script><script src="/x.js"></script>'
+    expect(inlineScriptHashes(html)).toEqual([sha256('a()')])
+  })
+
+  it('collapses duplicates and skips empty scripts', () => {
+    const html = '<script>x()</script><script>x()</script><script></script>'
+    expect(inlineScriptHashes(html)).toEqual([sha256('x()')])
+  })
+})
+
+describe('contentSecurityPolicy', () => {
+  it('puts the hashes in script-src', () => {
+    const policy = contentSecurityPolicy(["'sha256-abc'", "'sha256-def'"])
+    const directive = policy.split('; ').find((d) => d.startsWith('script-src'))
+    expect(directive).toBe("script-src 'self' 'sha256-abc' 'sha256-def'")
+  })
+
+  it('never admits inline script wholesale', () => {
+    // 'unsafe-inline' would let an injected script run, which is the thing the
+    // hashes exist to avoid.
+    const directive = contentSecurityPolicy(["'sha256-abc'"])
+      .split('; ')
+      .find((d) => d.startsWith('script-src'))
+    expect(directive).not.toContain('unsafe-inline')
+  })
+
+  it('keeps the rest of the policy pinned to the bundle', () => {
+    const policy = contentSecurityPolicy()
+    expect(policy).toContain("default-src 'self'")
+    expect(policy).toContain("object-src 'none'")
+    expect(policy).toContain("base-uri 'none'")
+    expect(policy).toContain("frame-src 'none'")
+    // Inline style is what the export genuinely needs, and only style.
+    expect(policy).toContain("style-src 'self' 'unsafe-inline'")
+  })
+})
diff --git a/apps/desktop/electron/main/csp.ts b/apps/desktop/electron/main/csp.ts
new file mode 100644
index 0000000..a48d6c5
--- /dev/null
+++ b/apps/desktop/electron/main/csp.ts
@@ -0,0 +1,47 @@
+import { createHash } from 'node:crypto'
+
+/**
+ * The inline scripts Next's export ships, as CSP source expressions.
+ *
+ * A static export carries its Flight payload in inline `<script>` tags
+ * (`self.__next_f.push(...)`). Under `script-src 'self'` Chromium refuses every
+ * one of them, so React boots with no payload and renders nothing: a blank
+ * window. Hashing them keeps the policy strict — `'unsafe-inline'` would admit
+ * any injected script, and a nonce cannot work here because the HTML is a file
+ * on disk that is not regenerated per load.
+ *
+ * Matches any `<script>` without a `src`, whatever its other attributes, so an
+ * attribute Next adds later cannot silently drop a script out of the policy.
+ */
+export function inlineScriptHashes(html: string): string[] {
+  const scripts = [...html.matchAll(/<script\b(?![^>]*\bsrc\s*=)[^>]*>([\s\S]*?)<\/script>/gi)]
+  const hashes = scripts
+    .map((match) => match[1] ?? '')
+    .filter((body) => body !== '')
+    .map((body) => `'sha256-${createHash('sha256').update(body, 'utf8').digest('base64')}'`)
+  return [...new Set(hashes)]
+}
+
+/**
+ * The window's Content-Security-Policy.
+ *
+ * The renderer reaches the outside world only through IPC, so everything is
+ * pinned to the bundle's own origin; `scriptHashes` admits the export's inline
+ * payload and nothing else.
+ */
+export function contentSecurityPolicy(scriptHashes: readonly string[] = []): string {
+  return [
+    "default-src 'self'",
+    // Next's exported bundle inlines a small amount of style.
+    "style-src 'self' 'unsafe-inline'",
+    ["script-src 'self'", ...scriptHashes].join(' '),
+    "img-src 'self' data:",
+    "font-src 'self' data:",
+    // The renderer talks to the main process over IPC, not the network.
+    "connect-src 'self'",
+    "object-src 'none'",
+    "frame-src 'none'",
+    "base-uri 'none'",
+    "form-action 'none'",
+  ].join('; ')
+}
diff --git a/apps/desktop/electron/main/index.ts b/apps/desktop/electron/main/index.ts
index 13e5b64..8c69db3 100644
--- a/apps/desktop/electron/main/index.ts
+++ b/apps/desktop/electron/main/index.ts
@@ -1,8 +1,10 @@
+import { readFileSync } from 'node:fs'
 import { readFile } from 'node:fs/promises'
 import { join, normalize } from 'node:path'
 import { fileURLToPath } from 'node:url'
 import { app, BrowserWindow, protocol, shell } from 'electron'
 import { contentTypeFor, resolveBundlePath } from './bundle-path.js'
+import { contentSecurityPolicy, inlineScriptHashes } from './csp.js'
 import { registerIpc } from './ipc.js'
 import { checkForUpdates } from './services/updater.js'
 import { closeAllSessions } from './services/sessions.js'
@@ -41,15 +43,44 @@ protocol.registerSchemesAsPrivileged([
   { scheme: APP_SCHEME, privileges: { standard: true, secure: true, supportFetchAPI: true } },
 ])
 
+function bundleRoot(): string {
+  return normalize(join(here, '..', '..', 'out'))
+}
+
+/**
+ * The policy, computed once from the export the app will actually serve.
+ *
+ * Read eagerly rather than per request: the hashes come from index.html, and a
+ * policy that silently fell back to one without them would blank the window.
+ */
+let policy: string | null = null
+function bundlePolicy(): string {
+  if (policy === null) {
+    try {
+      policy = contentSecurityPolicy(inlineScriptHashes(readFileSync(join(bundleRoot(), 'index.html'), 'utf8')))
+    } catch {
+      policy = contentSecurityPolicy()
+    }
+  }
+  return policy
+}
+
 /** Serves the exported renderer, and nothing outside it. */
 function serveBundle(): void {
-  const root = normalize(join(here, '..', '..', 'out'))
+  const root = bundleRoot()
   protocol.handle(APP_SCHEME, async (request) => {
     const target = resolveBundlePath(root, new URL(request.url).pathname)
     if (!target) return new Response('Forbidden', { status: 403 })
     try {
       const body = await readFile(target)
-      return new Response(body, { headers: { 'content-type': contentTypeFor(target) } })
+      return new Response(body, {
+        headers: {
+          'content-type': contentTypeFor(target),
+          // Carried on the response itself, so the document is governed by the
+          // policy whether or not a webRequest listener is attached.
+          'content-security-policy': bundlePolicy(),
+        },
+      })
     } catch {
       return new Response('Not found', { status: 404 })
     }
@@ -94,22 +125,7 @@ function createWindow(): BrowserWindow {
     callback({
       responseHeaders: {
         ...details.responseHeaders,
-        'Content-Security-Policy': [
-          [
-            "default-src 'self'",
-            // Next's exported bundle inlines a small amount of style.
-            "style-src 'self' 'unsafe-inline'",
-            "script-src 'self'",
-            "img-src 'self' data:",
-            "font-src 'self' data:",
-            // The renderer talks to the main process over IPC, not the network.
-            "connect-src 'self'",
-            "object-src 'none'",
-            "frame-src 'none'",
-            "base-uri 'none'",
-            "form-action 'none'",
-          ].join('; '),
-        ],
+        'Content-Security-Policy': [bundlePolicy()],
       },
     })
   })
diff --git a/scripts/smoke-desktop.mjs b/scripts/smoke-desktop.mjs
index 4e61ec0..c71abf2 100755
--- a/scripts/smoke-desktop.mjs
+++ b/scripts/smoke-desktop.mjs
@@ -93,8 +93,41 @@ function checkRendererDelivery() {
   console.log('ok: the renderer is served over its own scheme, not file://.')
 }
 
+/**
+ * The policy the window will send must admit every inline script in the export.
+ *
+ * Serving the assets correctly is not sufficient: a Next export carries its
+ * Flight payload in inline `<script>` tags, and `script-src 'self'` refuses
+ * them. That shipped in v0.2.1 — the chunks loaded, React booted with no
+ * payload, and the window was blank. Assets loading and the page rendering are
+ * different facts, and only this one catches the second.
+ */
+async function checkPolicyAdmitsPayload() {
+  const { contentSecurityPolicy, inlineScriptHashes } = await import(join(desktop, 'dist-electron', 'main', 'csp.js'))
+  const html = readFileSync(join(desktop, 'out', 'index.html'), 'utf8')
+  const hashes = inlineScriptHashes(html)
+
+  if (hashes.length === 0) {
+    console.error('FAIL: no inline scripts found in the export — the hashing no longer matches what Next emits.')
+    console.error('A policy computed from this would blank the window.')
+    process.exit(1)
+  }
+
+  const policy = contentSecurityPolicy(hashes)
+  const scriptSrc = policy.split('; ').find((directive) => directive.startsWith('script-src')) ?? ''
+  const unadmitted = hashes.filter((hash) => !scriptSrc.includes(hash))
+
+  if (unadmitted.length > 0) {
+    console.error(`FAIL: ${unadmitted.length} inline scripts are not admitted by script-src; the window would be blank.`)
+    process.exit(1)
+  }
+
+  console.log(`ok: the policy admits all ${hashes.length} inline payload scripts.`)
+}
+
 await checkRendererAssets()
 checkRendererDelivery()
+await checkPolicyAdmitsPayload()
 
 if (!existsSync(electron)) {
   console.error('electron binary not found; run pnpm install first.')
