Fix: Stop lens-map vertex decoding on read failure

tests/test_frame.c

@@ -1469,6 +1469,31 @@ int main(void) {
       lens_map_destroy(&dloaded); unlink(dp_path); goto done;
     }
     lens_map_destroy(&dloaded);
+    /* Truncate within the first v3 vertex, including each terminal field.
+     * Failed reads must reject the map and release its partially read mesh. */
+    {
+      unsigned char prefix[316];
+      FILE *fixture = fopen(dp_path, "rb");
+      int fixture_failed = fixture == NULL ||
+          fread(prefix, 1, sizeof prefix, fixture) != sizeof prefix;
+      if (fixture != NULL && fclose(fixture)) fixture_failed = 1;
+      if (fixture_failed) {
+        fputs("lens-map truncation fixture read failed\n", stderr);
+        unlink(dp_path); goto done;
+      }
+      const size_t cuts[] = {232, 303, 304, 307, 308, 311, 312, 315};
+      for (size_t c = 0; c < sizeof cuts / sizeof cuts[0]; ++c) {
+        FILE *short_file = fopen(dp_path, "wb");
+        int short_failed = short_file == NULL ||
+            fwrite(prefix, 1, cuts[c], short_file) != cuts[c];
+        if (short_file != NULL && fclose(short_file)) short_failed = 1;
+        if (short_failed || !lens_map_read(dp_path, NULL, &dloaded) ||
+            dloaded.frames != NULL || dloaded.frame_count != 0) {
+          fputs("lens-map truncated vertex rejection regression failed\n", stderr);
+          lens_map_destroy(&dloaded); unlink(dp_path); goto done;
+        }
+      }
+    }
     /* Unknown wire code and non-finite/out-of-bounds DP fields must be rejected
      * by the shared schema validator, not accepted as a usable map. */
     {