Create client ids without crypto.randomUUID

crypto.randomUUID() is only defined in secure contexts (HTTPS or
localhost). Opened over plain HTTP from another machine in the LAN, the
circuit list editor failed with "crypto.randomUUID is not a function"
whenever it created a circuit, device row, circuit group or distribution
board component, including typing into the -frei- row.

createClientId() uses crypto.randomUUID() where available and otherwise
builds an RFC 4122 version 4 UUID from crypto.getRandomValues(), which
works in every context. AGENTS.md notes the rule.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/client-id.test.ts

@@ -0,0 +1,45 @@
+import assert from "node:assert/strict";
+import { webcrypto } from "node:crypto";
+import { describe, it } from "node:test";
+import { z } from "zod";
+import { createClientId } from "../src/frontend/utils/client-id.js";
+
+const uuidV4 = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/;
+
+describe("client id", () => {
+  it("uses crypto.randomUUID when the context provides it", () => {
+    const id = createClientId({
+      getRandomValues: () => {
+        throw new Error("fallback must not be used");
+      },
+      randomUUID: () => "11111111-2222-4333-8444-555555555555",
+    });
+    assert.equal(id, "11111111-2222-4333-8444-555555555555");
+  });
+
+  it("falls back to getRandomValues outside a secure context", () => {
+    const insecure = {
+      getRandomValues: webcrypto.getRandomValues.bind(webcrypto),
+    } as Pick<Crypto, "getRandomValues">;
+    const ids = new Set<string>();
+    for (let index = 0; index < 200; index += 1) {
+      const id = createClientId(insecure);
+      assert.match(id, uuidV4);
+      assert.equal(z.string().uuid().safeParse(id).success, true);
+      ids.add(id);
+    }
+    assert.equal(ids.size, 200);
+  });
+
+  it("sets version and variant bits regardless of the random bytes", () => {
+    const allOnes = {
+      getRandomValues: <T extends ArrayBufferView | null>(array: T) => {
+        if (array instanceof Uint8Array) {
+          array.fill(0xff);
+        }
+        return array;
+      },
+    } as Pick<Crypto, "getRandomValues">;
+    assert.equal(createClientId(allOnes), "ffffffff-ffff-4fff-bfff-ffffffffffff");
+  });
+});