Appendix A — MAGE Engineering Stacks

A.5 Resource Mediation

A.5.1 The Capability

Prevent actor timing from becoming accidental concurrency policy for a shared resource. When actors contend for a scarce resource, move admission policy out of their timing and into an explicit control.

A.5.2 When This Stack Earns Its Keep

Reach for it when:

A.5.3 The Composition

The Resource-Mediation stack: a declared resource policy routes all access through one mediator to a shared resource; live pressure is a dashed enhancement A solid load-bearing path runs top to bottom. RESOURCE POLICY declares which resource is scarce and what capacity is acceptable. The MEDIATOR routes every access through one admission point, admitting at most N actors. The SHARED RESOURCE sits below it, now governed by explicit policy rather than actor timing. One enhancement attaches as a dashed, open-arrowed feedback: LIVE PRESSURE can tighten or relax the effective capacity when justified, but only after the fixed policy and admission seam exist. N equals one and N greater than one are settings of the same mediator, not separate stacks. DECLARE MEDIATE ADAPT RESOURCE POLICY capacity · scope MEDIATOR admit ≤ N actors SHARED RESOURCE LIVE PRESSURE tighten / relax when justified load-bearing (required) enhancement (not required) Solid path: the load-bearing composition. Dashed attachment: a useful enhancement, not required. N=1 and N>1 are settings of the same mediator, not separate stacks.
Figure A.5-1. The resource-mediation composition. A RESOURCE POLICY states which resource is scarce and what capacity is acceptable; a MEDIATOR admits at most N actors through one admission point to the SHARED RESOURCE. A dashed LIVE PRESSURE loop tightens or relaxes effective capacity when justified. N=1 and N>1 are settings of the same mediator, not separate stacks. Solid path: the load-bearing composition. Dashed attachment: a useful enhancement, not required for the capability.

A.5.4 Constituent Moves

Table A.5-1.
MoveRole
DECLAREState which resource is scarce and what capacity is acceptable.
MEDIATERoute access through one admission point.
ADAPT(strengthens) Modify effective capacity from live pressure where justified.

A.5.5 Why These Travel Together

Unmediated contention makes resource availability an emergent property of actor timing—whoever starts first wins, and the policy is an accident. A mediator replaces that accident with explicit policy: one admission point and a declared capacity. The engineering move is not the semaphore; it is moving contention policy out of individual actors and into one shared control. Whether that control admits one actor or many is a setting, not a different mechanism.

Adaptive control can improve utilization, but only after a fixed policy and common admission point exist. Capacity cannot be tuned coherently when no single control owns it.

Mechanisms: exclusive mediator · bounded mediator · pressure-responsive admission

© James C. Davis, 2026–present