D513 - Invented region bases and the address map

Status: decided Date: 2026-09-26

Every fixed base orbistoun reserves is a named constant listed in docs/ADDRESS_MAP.md with its owner, and a test fails when a base is missing from the map, stale in it, listed at the wrong value, or within four gibibytes of another. Regions of orbistoun's own invention take bases in the 0x0000_5E2x_0000_0000 family.

Why: bases spread across many crates are discoverable only by search, and a base chosen without checking collided with the range the kernel hands out virtual reservations from, which changed what the guest did. A base is a constant with a name and a value, so the map and the source are two machine-readable sets a test can compare. The 0x5E2x family is claimed by nothing else.

Rejected:

• Choosing a base by reasoning about what is nearby: silently collided with an existing base.
• A prose-only map: drifts from the source with nothing to notice.
• Gating spans as well as starts: the map records starts, not lengths.