fix: generateId() fallback for insecure-context origins

Problem
  The phone-preview path (http://192.168.1.167:5173) is a non-secure
  origin. `window.crypto.randomUUID` is gated behind secure contexts
  (HTTPS / localhost / 127.0.0.1 / file://) so it's undefined there,
  and every optimistic-id call site crashed handleAdd with
  `TypeError: crypto.randomUUID is not a function`.

Fix
  apps/web/src/lib/utils/id.ts — generateId() uses crypto.randomUUID()
    when available, otherwise falls back to crypto.getRandomValues()
    + RFC 4122 §4.4 byte assembly. getRandomValues IS exposed on
    insecure contexts (unlike subtle), so the fallback is v4-compliant
    and cryptographically acceptable for client-side optimistic ids.
  Replaced crypto.randomUUID() at every call site:
    stores/lists.ts, stores/tasks.ts, sync/queue.ts, sync/undoQueue.ts
    routes/(app)/lists/[id]/+page.svelte
    routes/(app)/tasks/[id]/+page.svelte
  CLAUDE.md gotcha added: never call crypto.randomUUID() directly —
    always import generateId from $lib/utils/id.

Tests (written first, confirmed failing on main)
  src/lib/utils/id.test.ts (4 tests)
    U-01 returns UUID v4 when randomUUID is available
    U-02 falls back when randomUUID is undefined
    U-03 50 fallback-generated ids are all unique
    U-04 prefers randomUUID when present (doesn't drop into fallback)
  tests/e2e/insecure-context.test.ts (1 test)
    INS-01 stubs crypto.randomUUID = undefined via addInitScript,
      drives the add-item flow, confirms the row renders (if the
      old call site were still there, handleAdd would throw).

Verification
  just test-all → exit 0, 233 green, 2 skipped:
    34 pgTAP (unchanged)
    140 Vitest integration + 2 skipped presence (unchanged)
    15 Vitest unit (was 11, +4 generateId)
    44 Playwright (was 43, +1 INS-01)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/lib/utils/id.test.ts

@@ -0,0 +1,49 @@
+import { describe, it, expect, afterEach, vi } from 'vitest';
+import { generateId } from './id';
+
+const UUID_V4 = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;
+
+describe('generateId', () => {
+	afterEach(() => {
+		vi.unstubAllGlobals();
+	});
+
+	it('U-01: returns a UUID v4-shaped string when crypto.randomUUID is available', () => {
+		const id = generateId();
+		expect(id).toMatch(UUID_V4);
+	});
+
+	it('U-02: falls back when crypto.randomUUID is undefined (insecure-context case)', () => {
+		// Simulate an HTTP LAN origin: window.crypto exists but randomUUID is not exposed.
+		const baseCrypto = globalThis.crypto;
+		vi.stubGlobal('crypto', {
+			getRandomValues: baseCrypto.getRandomValues.bind(baseCrypto)
+			// no randomUUID
+		});
+
+		const id = generateId();
+		expect(id).toMatch(UUID_V4);
+	});
+
+	it('U-03: every call returns a unique value (uniqueness under fallback)', () => {
+		const baseCrypto = globalThis.crypto;
+		vi.stubGlobal('crypto', {
+			getRandomValues: baseCrypto.getRandomValues.bind(baseCrypto)
+		});
+
+		const ids = new Set(Array.from({ length: 50 }, generateId));
+		expect(ids.size).toBe(50);
+	});
+
+	it('U-04: prefers crypto.randomUUID when present (does not drop into fallback)', () => {
+		const spy = vi.fn(() => '11111111-1111-4111-8111-111111111111');
+		vi.stubGlobal('crypto', {
+			randomUUID: spy,
+			getRandomValues: globalThis.crypto.getRandomValues.bind(globalThis.crypto)
+		});
+
+		const id = generateId();
+		expect(spy).toHaveBeenCalledTimes(1);
+		expect(id).toBe('11111111-1111-4111-8111-111111111111');
+	});
+});

apps/web/src/lib/utils/id.ts

@@ -0,0 +1,33 @@
+/**
+ * Generate a RFC 4122 v4 UUID.
+ *
+ * `crypto.randomUUID()` is only exposed on secure contexts (HTTPS, localhost,
+ * 127.0.0.1, file://). The app is served over bare LAN IPs for on-device
+ * phone previews (e.g. http://192.168.1.167:5173) — a non-secure origin —
+ * where `randomUUID` is undefined and every optimistic-id call site crashed
+ * with `TypeError: crypto.randomUUID is not a function`.
+ *
+ * `crypto.getRandomValues` IS available on insecure contexts (unlike
+ * `crypto.subtle` which is gated), so the fallback here is v4-compliant and
+ * cryptographically acceptable for client-side optimistic ids.
+ *
+ * Background: https://developer.mozilla.org/en-US/docs/Web/API/Crypto/randomUUID
+ */
+export function generateId(): string {
+	// Secure-context fast path.
+	if (typeof globalThis.crypto?.randomUUID === 'function') {
+		return globalThis.crypto.randomUUID();
+	}
+
+	// Fallback: 16 random bytes → format per RFC 4122 §4.4.
+	const bytes = new Uint8Array(16);
+	globalThis.crypto.getRandomValues(bytes);
+
+	// Set version (4) and variant (10xx) bits.
+	bytes[6] = (bytes[6] & 0x0f) | 0x40;
+	bytes[8] = (bytes[8] & 0x3f) | 0x80;
+
+	const hex: string[] = [];
+	for (let i = 0; i < 16; i++) hex.push(bytes[i].toString(16).padStart(2, '0'));
+	return `${hex.slice(0, 4).join('')}-${hex.slice(4, 6).join('')}-${hex.slice(6, 8).join('')}-${hex.slice(8, 10).join('')}-${hex.slice(10, 16).join('')}`;
+}