Tighten RSBK package-format validation for review remediation

Reject NUL/control bytes and Windows-hostile names in entry names, relax
the over-broad ".." substring ban to component-only, close the
trailing-garbage gap on empty manifests, and relocate the package
CMake subdirectory to its ladder home.

tests/test_package_manifest.cpp

@@ -102,13 +102,14 @@ static void testEmptyManifestRoundTrips() {
 // --- forward compatibility ---------------------------------------------------
 
 static void testUnknownKeysSkippedAtEveryLevel() {
-    // A future additive manifest: unknown keys at the root and inside an entry.
+    // A future additive manifest: unknown keys at the root, inside an entry,
+    // and inside the nested index blob itself.
     const std::string json =
         "{\"bankName\":\"B\",\"exported\":7,"
         "\"instrumentState\":{\"nested\":[1,2,{\"x\":\"y\"}]},"
         "\"entries\":[{\"name\":\"a.wav\",\"length\":10,\"hash\":\"h\","
         "\"futureField\":\"ignored\","
-        "\"index\":{\"version\":1,\"samples\":[{\"id\":\"s1\","
+        "\"index\":{\"version\":1,\"futureIndexField\":42,\"samples\":[{\"id\":\"s1\","
         "\"relativePath\":\"bank/a.wav\"}]}}],"
         "\"slots\":[],\"trailingUnknown\":null}";
     auto m = deserializeManifest(json);
@@ -159,6 +160,17 @@ static void testDuplicateEntryNamesRejectedBothWays() {
     CHECK(!deserializeManifest(dup).has_value());
 }
 
+static void testDuplicateEntriesKeyRejected() {
+    // A repeated "entries" key must not accumulate into two arrays' worth of
+    // entries — reject rather than silently union them.
+    const std::string json =
+        "{\"entries\":[{\"name\":\"a.wav\",\"length\":1,\"hash\":\"h\","
+        "\"index\":{\"version\":1,\"samples\":[{\"id\":\"s1\",\"relativePath\":\"p\"}]}}],"
+        "\"entries\":[{\"name\":\"b.wav\",\"length\":1,\"hash\":\"h\","
+        "\"index\":{\"version\":1,\"samples\":[{\"id\":\"s2\",\"relativePath\":\"q\"}]}}]}";
+    CHECK(!deserializeManifest(json).has_value());
+}
+
 // --- rejection: structural ---------------------------------------------------
 
 static void testEncodeRejectsUnrepresentableSample() {
@@ -223,6 +235,10 @@ static void testDecodeRejectsMalformedShapes() {
     auto json = serializeManifest(fixture());
     CHECK(json.has_value());
     CHECK(!deserializeManifest(*json + "x").has_value());
+    // Trailing garbage after the EMPTY-object shortcut specifically: this path
+    // returned early before reaching the eof check, so "{}JUNK" parsed valid.
+    CHECK(!deserializeManifest("{}JUNK").has_value());
+    CHECK(deserializeManifest("{}").has_value());
     // Truncation at a few JSON-level offsets (byte-level truncation of the whole
     // package is bank_package's suite).
     CHECK(!deserializeManifest(json->substr(0, json->size() / 2)).has_value());
@@ -236,6 +252,7 @@ int main() {
     testEncodeRejectsBadEntryName();
     testDecodeRejectsBadEntryName();
     testDuplicateEntryNamesRejectedBothWays();
+    testDuplicateEntriesKeyRejected();
     testEncodeRejectsUnrepresentableSample();
     testDecodeRejectsMalformedShapes();