Expose durable client timeline and reconnect contracts

[LeftTwixWand]

Outcome

Define durable client timeline and reconnect contracts that preserve causal continuity across disconnections.

Acceptance criteria

• Persist a durable timeline per owner.
• Record causal delivery metadata.
• Define a reconnect cursor.
• Bound replay.
• Resume the client after a disconnect.
• Keep authentication and edge policies outside the framework contract.

Non-goals

• Defining authentication providers, network-edge policy, or unbounded replay.