ADR 0120: note the shared/region interaction with hq 128

A roster fact may be shared — written into a marked region of the machine's
file (into: block, hq 128) rather than as the whole file. The template
renders the content; shared decides how the host lays it down. Composes with
hq 128: the region mechanism is the host's, the format is the module's.

02-DECISIONS/0120-a-roster-fact-carries-its-format-as-a-template.md

@@ -74,6 +74,15 @@ The two built-in projections render through the same path any module uses:
 - **dnsmasq's zones** move into dnsmasq. The `local=`/`address=` grammar is dnsmasq's configuration
   language, and it now lives in dnsmasq's manifest, where the module that runs dnsmasq owns it.
 
+**A fact also says whether its file is the mesh's whole or a region of the machine's.** A hosts file
+is the machine's — its `localhost`, the operator's lines, another tool's marked blocks — so
+`node-names` is `shared`: the mesh owns only its region and keeps the rest byte for byte, the host
+laying it down `into: block`
+([ADR 0102](0102-the-mesh-writes-into-a-shared-file-never-over-it.md), hq issue 128). A resolver's
+zones file is the mesh's whole, and is not shared. The template renders the content either way;
+`shared` decides how the host writes it. This composes with hq 128 rather than replacing it: the
+region *mechanism* is the host's, the region's *format* is the module's template.
+
 **The names-vs-machines distinction is the template's choice** ([04-ISSUES/111](../04-ISSUES/111-the-resolver-is-told-names-the-mesh-serves-not-only-machines/00-report.md)):
 a container's hosts ranges `.Names`, so a routed name resolves to the machine serving it; a resolver
 told the mesh's suffix is its own ranges `.Machines`, or a routed name written there with the suffix