D112 — Reserved local endpoint defaults

Status: implemented (2026-07-28).

Decision. New local service configurations listen on 127.0.0.1:39273, and a new client uses http://localhost:39273/mcp. The dependency-light internal/defaults package owns the port, listen address, and MCP URL so the native-service and client first-run paths cannot drift. cartographer serve without an explicit HTTP setting remains stdio.

Compatibility. Existing server YAML and .cartographer.yaml values, including an explicit port 8080, remain authoritative and are never rewritten. The normal precedence rules continue to apply: server flag > environment > YAML > default; client existing YAML > CARTOGRAPHER_SERVER_URL > local default.

Rationale. Port 8080 is frequently occupied by local development servers and infrastructure. Reserving one project-local default avoids that collision without making the endpoint a protocol requirement or migrating an operator's chosen configuration.