P1: add durable continuation for escalated workflows

[safal207]

Parent

#216

Goal

Store unresolved CI/CD workflows so they can resume safely after new evidence or human input.

Required state

• action and trajectory IDs;
• escalation reason;
• checkpoint reference;
• continuation reference;
• expiry and retry policy;
• repository, PR, base, and head;
• pending resolution.

Acceptance criteria

• duplicate resume is idempotent;
• changed base, head, or workspace requires revalidation;
• resumed context does not reuse prior merge permission;
• expired continuation fails closed;
• stale checkpoint cannot replace newer state;
• resume triggers a fresh Action Envelope evaluation;
• tests cover missing review, unknown mergeability, temporary outage, duplicate resume, target drift, and invalid permission carry-over.

Dependencies

• P1: define CI operational checkpoint and resume contract #218, P1: add causal CI/CD lifecycle event envelope #219, and durable coordination.