hgraph-persistence

Durable record/replay and frame storage for hgraph (RFC 0025): the FrameStore (memory / local filesystem / S3, Arrow IPC / Parquet), the frame-backed record/replay/compare overloads for the core operator markers, and the DataFrameStorage compatibility surface.

The public C++ ObjectStore is the durable metadata substrate shared by checkpoint/recovery and the versioned dataflow fabric. It provides:

• immutable create-if-absent with distinct created, idempotent, and conflict outcomes;
• typed absent reads carrying an opaque version token when present, with backend failures reported separately as ObjectStoreError;
• deterministic lexicographic prefix paging;
• compare/exchange for small named references; and
• memory, local-filesystem, and S3 strategies behind one owning erased handle.

Local immutable publication uses atomic filesystem creation and reference CAS uses cross-process file locking plus atomic replacement. S3 conditional writes are sent with If-None-Match / If-Match and AWS Signature V4 through libcurl; they are not emulated with a read followed by an unconditional write. FrameStore immutable local and S3 writes use this same backend publication path after serialising the Frame. This requires one additional serialized-Frame-sized buffer for an immutable local or S3 write; mutable FrameStore writes retain their streaming path.

Wheel builds embed a pinned private curl for conditional S3 requests. A shared hgraph::persistence library carries that implementation itself; consumers of a static installed C++ library must provide CURL::libcurl version 7.75 or newer at the final link.

Installing and importing hgraph_persistence registers the "hgraph.persistence.frame" backend with the shared hgraph runtime; selecting that backend (set_record_replay_config) activates it from unchanged hgraph imports.

Runnable Python examples for direct record/replay, transparent component modes, and keyed time-series storage are in python/examples.