ConversationChainStoreProtocol

Get and set named dictionaries within a conversation chain.

Implementations must satisfy these requirements:

• Persistence: after :meth:set succeeds, subsequent :meth:get calls with the same conversation chain ID and key return an equal, unaltered dictionary for the supported lifetime.
• Isolation: treat (conversation_chain_id, key) as the record identity. Operations on one identity must not read or modify another identity.
• Capacity: accept dictionaries containing at least 512 total characters across all keys and values.
• Thread safety: calls for different keys may overlap.
• Error handling: return None only when the key is absent and raise an exception for all other failures. If a dictionary exceeds an implementation limit, reject it without truncating it or modifying the previously stored value.

Implementations may optionally support TTL but it is recommended to prevent unbounded growth. When supported, a write-sliding TTL is preferred: :meth:set renews the lifetime and :meth:get does not.