fix: compare the coredump build SHA without reading past the array

app_elf_sha256 has no terminator (IDF 4.4 fills all 17 bytes), so strcmp
never matched the running build and %s printed whatever followed it.  Copy
it into a terminated buffer first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/SomfyController.ino

@@ -86,7 +86,11 @@ void setup() {
 #endif
     // The backtrace only decodes against the firmware.elf of the build that
     // crashed, so say whether that is the one running now.
-    const char *crashedSha = (const char *)summary.app_elf_sha256;
+    // app_elf_sha256 isn't always terminated, so copy it before comparing or
+    // printing it.
+    char crashedSha[APP_ELF_SHA256_SZ];
+    static_assert(sizeof(crashedSha) <= sizeof(summary.app_elf_sha256), "copy would read past app_elf_sha256");
+    SETCHARPROP(crashedSha, (const char *)summary.app_elf_sha256, sizeof(crashedSha));
     char runningSha[APP_ELF_SHA256_SZ] = {0};
     getRunningElfSha(runningSha, sizeof(runningSha));
     if(strcmp(crashedSha, runningSha) == 0)

test/test_utils/test_utils.cpp

@@ -79,6 +79,15 @@ static void test_setcharprop_truncates_long_value() {
   SETCHARPROP(prop, "abcdefgh", sizeof(prop));
   TEST_ASSERT_EQUAL_STRING("abcd", prop);
 }
+static void test_setcharprop_unterminated_source() {
+  // A coredump's app_elf_sha256 can be full of hex digits with no terminator.
+  // The copy must stop inside the array and come out as a comparable string.
+  const char crashed[17] = {'0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f','9'};
+  char sha[sizeof(crashed)];
+  SETCHARPROP(sha, crashed, sizeof(sha));
+  TEST_ASSERT_EQUAL_STRING("0123456789abcdef", sha);
+  TEST_ASSERT_EQUAL_INT(0, strcmp(sha, "0123456789abcdef"));
+}
 
 /*********************************************************************
  * sortArray / sortArrayReverse
@@ -202,6 +211,7 @@ int main(int argc, char **argv) {
   RUN_TEST(test_toBoolean_unknown_uses_default);
   RUN_TEST(test_setcharprop_copies_short_value);
   RUN_TEST(test_setcharprop_truncates_long_value);
+  RUN_TEST(test_setcharprop_unterminated_source);
   RUN_TEST(test_sortArray_ascending);
   RUN_TEST(test_sortArrayReverse_descending);
   RUN_TEST(test_sortArray_custom_comparator);