fix: resolve lint failures (clang-format, cppcheck)

- Add null guard to store_set_error() to prevent null pointer deref
- Narrow variable scopes for tests, note, dst_idx per cppcheck
- Remove redundant direct_callers<=2 condition (always true after >=3 check)
- Run clang-format on all affected files

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: maplenk