fix(license): abort on invalid or unvalidatable key instead of silent free fallback

A supplied license key the server rejects, or one that cannot be validated
(server unreachable, no cache), now raises instead of silently downloading the
free binary. No-key (keyless) and valid-key (Pro) paths unchanged. Python, JS,
and .NET, with mirror tests in each.

js/src/download.ts

@@ -127,9 +127,18 @@ export async function ensureBinary(
         );
       }
     } else if (info) {
-      console.log(`[cloakbrowser] License validation failed (plan=${info.plan}), using free tier`);
+      // Key supplied but rejected — abort, never downgrade to free.
+      throw new Error(
+        `CloakBrowser Pro: license key is invalid or expired (plan=${info.plan}). ` +
+          `Check CLOAKBROWSER_LICENSE_KEY, or unset it to use the free binary.`,
+      );
     } else {
-      console.log("[cloakbrowser] License validation unavailable, using free tier");
+      // Key supplied but unvalidatable (server down, no cache) — abort.
+      throw new Error(
+        "CloakBrowser Pro: license could not be validated (server unreachable " +
+          "and no cached validation). Retry in a moment, or unset " +
+          "CLOAKBROWSER_LICENSE_KEY to use the free binary.",
+      );
     }
   }
 

js/tests/update.test.ts

@@ -547,6 +547,23 @@ describe("preview Pro selection", () => {
       errSpy.mock.calls.some((c) => String(c[0]).includes("no preview build is available")),
     ).toBe(false);
   });
+
+  it("aborts (never free) when the server rejects the key", async () => {
+    delete process.env.CLOAKBROWSER_DOWNLOAD_URL;
+    vi.spyOn(globalThis, "fetch").mockResolvedValue({
+      ok: true,
+      json: async () => ({ valid: false, plan: "solo", expires: null }),
+    } as Response);
+
+    await expect(ensureBinary("cb_bad")).rejects.toThrow(/invalid or expired/);
+  });
+
+  it("aborts (never free) when the key cannot be validated (server down, no cache)", async () => {
+    delete process.env.CLOAKBROWSER_DOWNLOAD_URL;
+    vi.spyOn(globalThis, "fetch").mockRejectedValue(new Error("network down"));
+
+    await expect(ensureBinary("cb_test")).rejects.toThrow(/could not be validated/);
+  });
 });
 
 describe("ensureBinary", () => {