Longfellow ZK 1.x ABI policy

The shared library SONAME is liblongfellow-zk.so.1. Compatible 1.x releases retain SONAME 1; a future incompatible ABI requires a new major release and SONAME. Only declarations marked LONGFELLOW_ZK_API are supported dynamic-link entry points. Header-only templates and inline gadgets remain compiled by the consumer.

Callers own memory that they allocate and must not transfer STL containers or allocator-owned objects across this ABI. The library is built without an ABI guarantee across different compiler or C++ standard-library versions. Its public operations do not throw as part of their contract; builds that disable exceptions and RTTI remain supported, including the existing WASI workflow. Thread safety is operation-specific: callers must synchronize shared mutable objects, while independent calls that use caller-owned state are safe.