Define OpenCode task-pool/server direction for dispatched agent work

[BASIC-BIT]

Parent epic: #43

Problem:

VRDex wants to move toward pooled, dispatchable, resumable agent work instead of relying only on ad hoc interactive sessions.

Scope:

• define the desired OpenCode server/task-pool model
• define atomic jobs vs long-lived sessions as first-class concepts
• define agent roster/discoverability needs
• define how agents may request new work through an orchestrator path

Non-goals:

• shipping the hosted server immediately
• solving every cross-host scheduling concern in one pass

Acceptance criteria:

• the task-pool/server direction is documented clearly
• atomic jobs vs resumable sessions are differentiated clearly
• the idea is concrete enough to map into later implementation issues without relying on chat history

Soft dependencies

• Define orchestrator/supervisor loop and resumable-session policy #48 Define orchestrator/supervisor loop and resumable-session policy

Soft dependents

• Detect mergeability regressions and auto-dispatch recovery work #52 Detect mergeability regressions and auto-dispatch recovery work