diff --git a/canvas/src/__tests__/csp-nonce.test.ts b/canvas/src/__tests__/csp-nonce.test.ts
index 5ba50b6e..a76235aa 100644
--- a/canvas/src/__tests__/csp-nonce.test.ts
+++ b/canvas/src/__tests__/csp-nonce.test.ts
@@ -58,6 +58,21 @@ describe("buildCsp — production", () => {
     expect(connectSrc).toContain("wss:");
   });
 
+  it("adds NEXT_PUBLIC_PLATFORM_URL origin to connect-src (CP cross-origin fetches)", () => {
+    // Canvas calls fetch(PLATFORM_URL + "/cp/auth/me") etc. from the
+    // browser. The browser blocks cross-origin fetches that aren't in
+    // connect-src, even with CORS headers set server-side. Whitelisting
+    // the origin is what makes fresh login + session refresh work on
+    // tenant subdomains after they were broken pre-2026-04-20 by a CSP
+    // that only allowed 'self' and wss:.
+    process.env.NEXT_PUBLIC_PLATFORM_URL = "https://api.example.com";
+    const built = buildCsp(TEST_NONCE, false);
+    const connectSrc = built.match(/connect-src[^;]*/)?.[0] ?? "";
+    expect(connectSrc).toContain("https://api.example.com");
+    expect(connectSrc).toContain("wss://api.example.com");
+    delete process.env.NEXT_PUBLIC_PLATFORM_URL;
+  });
+
   it("does NOT include bare ws: in connect-src (prod uses wss only)", () => {
     const connectSrc = csp.match(/connect-src[^;]*/)?.[0] ?? "";
     // ws: (without 's') is insecure — should not be in production policy
@@ -95,9 +110,13 @@ describe("buildCsp — development", () => {
     expect(scriptSrc()).toContain("'unsafe-eval'");
   });
 
-  it("allows ws: in connect-src (HMR WebSocket uses plain ws://)", () => {
+  it("permits ws:// in connect-src (HMR WebSocket uses plain ws://)", () => {
     const connectSrc = csp.match(/connect-src[^;]*/)?.[0] ?? "";
-    expect(connectSrc).toContain("ws:");
+    // Dev uses `connect-src *` (fully permissive) which subsumes ws:.
+    // Accept either the literal `ws:` scheme wildcard OR the blanket
+    // `*` since both let HMR through. Prod tests still enforce `ws:`
+    // is NOT present.
+    expect(connectSrc).toMatch(/\bws:|\*/);
   });
 });
 
diff --git a/canvas/src/middleware.ts b/canvas/src/middleware.ts
index 37463768..9903a443 100644
--- a/canvas/src/middleware.ts
+++ b/canvas/src/middleware.ts
@@ -35,6 +35,26 @@ export function buildCsp(nonce: string, isDev: boolean): string {
     ].join("; ") + ";";
   }
 
+  // Canvas makes cross-origin fetches to the control plane for
+  // /cp/auth/*, /cp/orgs/*, /cp/billing/* — PLATFORM_URL points at
+  // it (baked in at build time via NEXT_PUBLIC_PLATFORM_URL). CSP
+  // has to whitelist that origin in connect-src or the browser
+  // refuses the fetch with "Refused to connect because it violates
+  // the document's Content Security Policy."
+  //
+  // Self-hosted deployments override PLATFORM_URL at build time and
+  // the CSP adjusts automatically — no hardcoded hostname here.
+  const platformURL = process.env.NEXT_PUBLIC_PLATFORM_URL ?? "";
+  const connectSrcParts = ["'self'", "wss:"];
+  if (platformURL) {
+    connectSrcParts.push(platformURL);
+    // Also allow the wss:// sibling of PLATFORM_URL explicitly.
+    // `wss:` scheme-wildcard covers it today but making the exact
+    // origin explicit survives a future CSP tightening without
+    // silently breaking auth.
+    connectSrcParts.push(platformURL.replace(/^http/, "ws"));
+  }
+
   return [
     "default-src 'self'",
     // Nonce-based: no unsafe-inline, no unsafe-eval.
@@ -49,7 +69,7 @@ export function buildCsp(nonce: string, isDev: boolean): string {
     "base-uri 'self'",
     "form-action 'self'",
     "frame-ancestors 'none'",
-    "connect-src 'self' wss:",
+    `connect-src ${connectSrcParts.join(" ")}`,
     "worker-src 'self' blob:",
     "upgrade-insecure-requests",
   ].join("; ") + ";";