test: prove canonical directory package identity

test/testenv/testenv.ww

@@ -217,6 +217,39 @@ export fn occurrences(haystack: str, needle: str) i32 = {
 	return count;
 };
 
+// Expected semantic identity for a canonical absolute directory that is not
+// representable below an active source root. Keep this independent observer
+// byte-for-byte aligned with the documented driver protocol.
+export fn localpackageidentity(dir: str, leaf: str) str = {
+	let out: []u8 = alloc([], (dir.len * 4 + leaf.len + 16): u64)!;
+	let prefix: str = "__wwlocal.p";
+	let i: i32 = 0;
+	for (i < prefix.len) { append(out, prefix[i]); i += 1; };
+	let hex: str = "0123456789abcdef";
+	i = 0;
+	for (i < dir.len) {
+		let c: u8 = dir[i];
+		if ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')
+			|| (c >= '0' && c <= '9')) {
+			append(out, c);
+		} else if (c == '_') {
+			append(out, '_'); append(out, 'u');
+		} else if (c == '/') {
+			append(out, '_'); append(out, 's');
+		} else {
+			let high: i32 = (c / 16u8): i32;
+			let low: i32 = (c % 16u8): i32;
+			append(out, '_'); append(out, 'x');
+			append(out, hex[high]); append(out, hex[low]);
+		};
+		i += 1;
+	};
+	append(out, '.');
+	i = 0;
+	for (i < leaf.len) { append(out, leaf[i]); i += 1; };
+	return strings.frombytes(out);
+};
+
 // Byte-lexicographic order, so directory listings sort identically on
 // every host regardless of locale.
 export fn lexless(a: str, b: str) bool = {