fix: blank page on non-localhost HTTP (secure-context crypto.randomUUID)

crypto.randomUUID() is secure-context-only — undefined on plain-HTTP
non-localhost origins (e.g. http://arch-razer:24204), so createAppStore threw
during mount and nothing rendered. Add src/app/uuid.ts randomId(): prefer
crypto.randomUUID when present, else build a v4 from crypto.getRandomValues
(available in insecure contexts), else Math.random fallback. Use it for the
conversation id.

Verified: svelte-check 0/0, vitest 221, build ok.

1 files changed, 65 insertions, 0 deletions

diff --git a/src/app/uuid.ts b/src/app/uuid.ts
new file mode 100644
index 0000000..ae39d4d
--- /dev/null
+++ b/src/app/uuid.ts
@@ -0,0 +1,65 @@
+const HEX = "0123456789abcdef";
+
+function hexChar(n: number): string {
+	return HEX.charAt(n & 0xf);
+}
+
+function hexFromBytes(bytes: Uint8Array): string {
+	let out = "";
+	for (let i = 0; i < bytes.length; i++) {
+		const b = bytes[i] as number;
+		out += hexChar(b >> 4);
+		out += hexChar(b);
+	}
+	return out;
+}
+
+function formatV4(rand: Uint8Array): string {
+	const h = hexFromBytes(rand);
+	return (
+		h.slice(0, 8) +
+		"-" +
+		h.slice(8, 12) +
+		"-4" +
+		h.slice(13, 16) +
+		"-" +
+		((parseInt(h.slice(16, 18), 16) & 0x3f) | 0x80).toString(16).padStart(2, "0") +
+		h.slice(18, 20) +
+		"-" +
+		h.slice(20, 32)
+	);
+}
+
+function uuidFromGetRandomValues(): string {
+	const buf = new Uint8Array(16);
+	crypto.getRandomValues(buf);
+	buf[6] = ((buf[6] as number) & 0x0f) | 0x40;
+	buf[8] = ((buf[8] as number) & 0x3f) | 0x80;
+	return formatV4(buf);
+}
+
+function uuidFromMathRandom(): string {
+	let s = "";
+	for (let i = 0; i < 36; i++) {
+		if (i === 8 || i === 13 || i === 18 || i === 23) {
+			s += "-";
+		} else if (i === 14) {
+			s += "4";
+		} else if (i === 19) {
+			s += hexChar(Math.floor(Math.random() * 4) + 8);
+		} else {
+			s += hexChar(Math.floor(Math.random() * 16));
+		}
+	}
+	return s;
+}
+
+export function randomId(): string {
+	if (typeof crypto !== "undefined" && typeof crypto.randomUUID === "function") {
+		return crypto.randomUUID();
+	}
+	if (typeof crypto !== "undefined" && typeof crypto.getRandomValues === "function") {
+		return uuidFromGetRandomValues();
+	}
+	return uuidFromMathRandom();
+}