[checkpoint] Resume opencode_agent from durable OpenCode sessions #3269

Parent

Child of #3221 and #3024.

Runtime state

responses_api_agents/opencode_agent/app.py delegates authoritative continuation state to the OpenCode process/session database and workspace.

Provider adapter requirements

Implement the shared opaque-runtime contract with provider/version, native session or thread ID, safe-boundary sequence, isolated workspace/session bundle manifest and digest, model-call lineage, resource/MCP metadata, exact resume operation, and stale-process fencing. Advertise export/restore only after native resume is proven; otherwise declare restart-only explicitly.

Acceptance criteria

• Persist an isolated OpenCode session and resume command; reconcile restored boundaries with invocation-owned model calls introduced by PR feat(observability): correlate OpenCode calls with invocations #2884.
• Kill and replace the agent server after each provider-emitted completed turn, then resume without duplicated model/tool effects.
• Session databases and workspaces are isolated by rollout attempt.
• Old processes cannot emit responses or mutate state after replacement.
• Missing, corrupt, or incompatible bundles fail restore before activation.
• Duplicate resume is idempotent or rejected deterministically.