0117 review: seat table row + decision cited, networkd/dhcpcd lines match the modules, block placement, dispatcher scope, references

02-DECISIONS/0117-a-machines-uplink-is-a-seat.md

@@ -34,9 +34,9 @@ by accident:
 - **The private network's interface is exposed to the manager.** A manager that considers
   every interface its own may try to configure `mesh0`, or tear it down on a profile change.
   Nothing tells it not to.
-- **Two managers on one machine go unnoticed.** Of the four machines adopted so far, one runs
-  systemd-networkd, two run NetworkManager, and one runs NetworkManager *and* dhcpcd at once:
-  two programs that each believe they own the machine's addresses and its resolver file.
+- **Two managers on one machine go unnoticed.** Among the machines adopted so far, one runs
+  NetworkManager *and* dhcpcd at once: two programs that each believe they own the machine's
+  addresses and its resolver file.
   Nothing detected it, because nothing in the mesh knows the role exists.
 
 The machines differ in a way that matters: servers are wired and never move, while
@@ -72,13 +72,16 @@ other:
 
 - the manager's package, and its service running and enabled at boot;
 - the manager's own configuration that leaves the resolver file to the mesh (`dns=none` for
-  NetworkManager, `nohook resolv.conf` for dhcpcd, and for systemd-networkd the equivalent
-  that stops it handing DNS to a resolver the machine does not use);
+  NetworkManager, `nohook resolv.conf` for dhcpcd, and nothing for systemd-networkd, which
+  never writes the resolver file);
 - the manager's own configuration that leaves the private network's interface alone
-  (NetworkManager's `unmanaged-devices` naming `mesh0`; for systemd-networkd, no network file
-  of the module's matches it);
+  (NetworkManager's `unmanaged-devices` naming `mesh0`; dhcpcd's `denyinterfaces mesh0`; for
+  systemd-networkd a network file of the module's matching `mesh0` as `Unmanaged=yes`);
 - each as a drop-in beside the manager's main file where the manager reads one, and written
-  *into* a shared file otherwise ([ADR 0102](0102-the-mesh-writes-into-a-shared-file-never-over-it.md));
+  *into* a shared file otherwise, as a marked region the host owns
+  ([ADR 0102](0102-the-mesh-writes-into-a-shared-file-never-over-it.md)'s idea for text files),
+  placed where the manager reads it as global — at the start of `dhcpcd.conf`, above any
+  `interface` line, because every line after one belongs to that interface;
 - the service **reloaded** when a drop-in changes, never restarted — a restart drops the link,
   and the link is the mesh's own channel to the machine. **A manager that cannot reload is not
   restarted instead:** its setting takes effect at the manager's next start. Measured on the
@@ -102,11 +105,23 @@ them, and the module's `access`, if it needs one, is read-only.
   replaced under another name.
 - A machine running two managers is found at assignment: the second holder is refused, and the
   operator decides which manager the machine keeps before either module is taken.
-- Workstations keep joining networks the way they always have. The host already cooperates
-  with the manager — its dispatcher hook wakes it on every connectivity change — and nothing
-  here changes that.
+- Workstations keep joining networks the way they always have. Under NetworkManager and
+  systemd-networkd the host already cooperates with the manager — its dispatcher hook wakes it
+  on every connectivity change — and nothing here changes that. A dhcpcd-only machine has no
+  such hook, and nothing here adds one.
 - The seat table gains one entry: `the-uplink`, node scope, delivering nothing, decided here.
 - **Not decided here:** whether the mesh should ever *offer* known networks to a machine — a
   sealed, add-only list the operator curates once for all workstations. That is a different
   question (the mesh holding credentials for links it must never be able to break) and gets its
   own record if it is wanted.
+
+## References
+
+- [ADR 0110](0110-a-seat-is-a-module-assignment-from-a-closed-set.md): the closed set this seat joins;
+  [to-be 26](../03-DESIGN/01-to-be/26-the-seats.md): the seat table
+- [ADR 0102](0102-the-mesh-writes-into-a-shared-file-never-over-it.md): written into, never over
+- [ADR 0051](0051-shared-data-is-the-operators.md): what is the operator's stays the operator's
+- mesh-controller `internal/catalogue/seats.go` (the seat), `internal/overlay/generator.go` (the
+  mesh installs on top of the machine's own networking)
+- mesh-catalog `modules/networkmanager`, `modules/systemd-networkd`, `modules/dhcpcd`
+- mesh-host `internal/apply/block.go` (a file written into a marked region, `at` start or end)