Add a cache to data link layer for control frames with hash

components/dataLink/include/Frames.h

@@ -30,8 +30,11 @@
 #define CONTROL_FRAME_OVERHEAD 9
 #define GENERIC_FRAME_OVERHEAD 14
 
+#define CONTROL_FRAME_HASH_SIZE 4   // 4-byte FNV-1a hash prepended to control frame payload on the wire
+
 #define MAX_GENERIC_DATA_LEN (MAX_FRAME_SIZE - GENERIC_FRAME_OVERHEAD)
-#define MAX_CONTROL_DATA_LEN (MAX_FRAME_SIZE - CONTROL_FRAME_OVERHEAD)
+// Control data max accounts for the 4-byte hash prefix that is prepended on transmit and stripped on receive
+#define MAX_CONTROL_DATA_LEN (MAX_FRAME_SIZE - CONTROL_FRAME_OVERHEAD - CONTROL_FRAME_HASH_SIZE)
 
 //Generic Frame Fragment ACK
 #define GENERIC_FRAG_ACK_DATA_SIZE 7
@@ -107,6 +110,17 @@ typedef struct _fragment_metadata {
     uint16_t num_fragments_rx;
 } FragmentMetadata;
 
+/**
+ * @brief Entry in the receiver-side control-frame LFU lookup table
+ */
+typedef struct _control_frame_lut_entry {
+    uint32_t hash;                        // FNV-1a hash of the original payload (key)
+    std::vector<uint8_t> message;         // Cached decoded payload (sans hash prefix)
+    FrameHeader header;                   // Cached frame header
+    uint32_t frequency;                   // Hit count – used for LFU eviction
+    bool valid;                           // Is this slot populated?
+} ControlFrameLutEntry;
+
 typedef struct _receive_metadata{
     std::unique_ptr<std::vector<uint8_t>> data;
     uint16_t data_len;