feat: in-page detection with overlay UI and 5-char signatures

sig.js

@@ -0,0 +1,53 @@
+import zwus from 'zwus';
+
+export const SIG_PREFIX = '\u{200D}\u{200B}\u{00AD}';
+
+export const SIG = {
+    3: '\u{200D}\u{200B}\u{00AD}\u{180E}\u{200D}',
+    6: '\u{200D}\u{200B}\u{00AD}\u{200C}\u{200D}',
+    8: '\u{200D}\u{200B}\u{00AD}\u{200C}\u{200C}'
+};
+
+export const CIPHERS = {
+    1: 'SPECK48_96CTR',
+    2: 'SPECK32_64ECB (insecure)'
+};
+
+export const CIPHER_TO_ID = Object.fromEntries(
+    Object.entries(CIPHERS).map(([k, v]) => [v, +k])
+);
+
+export function makeSig(base, cipher) {
+    let s = SIG[base];
+    const id = CIPHER_TO_ID[cipher];
+    if (id) {
+        const zwDigits = Array.from(id.toString(base).padStart(3, '0'), d => zwus[base][d]).join('');
+        s += zwus[base].unifier + zwus[base][0] + zwDigits;
+    }
+    return s;
+}
+
+export function parseSig(text) {
+    if (!text.includes(SIG_PREFIX)) return null;
+    const base = Object.keys(SIG).find(b => text.includes(SIG[b]));
+    if (!base) return null;
+    const sigIdx = text.indexOf(SIG[base]);
+    const after = text.slice(sigIdx + SIG[base].length);
+    const barrier = zwus[base].unifier + zwus[base][0];
+    if (after.startsWith(barrier)) {
+        const zwDigits = Array.from(after.slice(barrier.length, barrier.length + 3));
+        const digits = zwDigits.map(z => Object.keys(zwus[base]).find(k => zwus[base][k] === z)).join('');
+        const cipher = CIPHERS[parseInt(digits, base)];
+        const payload = after.slice(barrier.length + 3);
+        const sigLen = SIG[base].length + barrier.length + 3;
+        return { base, cipher, payload, sigIdx, sigLen };
+    }
+    return { base, cipher: 'PLAIN', payload: after, sigIdx, sigLen: SIG[base].length };
+}
+
+export function getPayloadEnd(text, base, startOffset) {
+    const zw = new Set(Object.values(zwus[base]));
+    let i = startOffset;
+    while (i < text.length && zw.has(text[i])) i++;
+    return i;
+}