Simplify to a more obviously fake SHA256 algorithm

test/mocks/SHA256.h

@@ -2,43 +2,26 @@
 
 #include <stdint.h>
 #include <stddef.h>
-#include <string.h>
 
 // Mock SHA256 class for native testing.
-// Provides a deterministic stand-in so code can hash data without Arduino crypto deps.
+// Provides a fixed stand-in so code can compile without Arduino crypto deps.
+// update() and resetHMAC() ignore all input; finalize() and finalizeHMAC()
+// fill the requested output buffer with 0x11 bytes.
 class SHA256 {
-  uint32_t state_ = 2166136261u;
-
 public:
-  void update(const void* data, size_t len) {
-    update(static_cast<const uint8_t*>(data), len);
-  }
+  void update(const void*, size_t) {}
 
-  void update(const uint8_t* data, size_t len) {
-    for (size_t i = 0; i < len; ++i) {
-      state_ ^= data[i];
-      state_ *= 16777619u;
-      state_ += 0x9E3779B9u;
-    }
-  }
+  void update(const uint8_t*, size_t) {}
 
   void finalize(uint8_t* hash, size_t hashLen) {
-    uint32_t value = state_;
     for (size_t i = 0; i < hashLen; ++i) {
-      value ^= value >> 13;
-      value *= 1274126177u;
-      hash[i] = static_cast<uint8_t>((value >> ((i & 3) * 8)) & 0xFF);
+      hash[i] = 0x11;
     }
   }
 
-  void resetHMAC(const uint8_t* key, size_t keyLen) {
-    state_ = 2166136261u;
-    update(key, keyLen);
-    state_ ^= 0x36363636u;
-  }
+  void resetHMAC(const uint8_t*, size_t) {}
 
-  void finalizeHMAC(const uint8_t* key, size_t keyLen, uint8_t* hash, size_t hashLen) {
-    update(key, keyLen);
+  void finalizeHMAC(const uint8_t*, size_t, uint8_t* hash, size_t hashLen) {
     finalize(hash, hashLen);
   }
 };