nix: comments state current behaviour, not history

Rewrite comments and option descriptions under nix/ that narrate how the
code got here ("used to", "new name", "sat at the TOP", "no longer",
renamed/moved narration, attributions) to say what the code does now and
why. Comments and description strings only; no logic changes.

Files in open PR #4970's diff are left alone. Refs #3902

nix/host-modules/swarm-authelia.nix

@@ -171,7 +171,7 @@ let
   # 🏷️ The id EXTENDS the hive's own (`hive-<name>-agent`) rather than taking a
   # prefix of its own (`agent-<name>`), because that reads as *the agent called
   # `<name>`* — which is the one thing this identity does not carry. The cost is
-  # that the two ids are no longer distinguishable by prefix, so the responder's
+  # that the two ids are not distinguishable by prefix, so the responder's
   # agent rule must be tried BEFORE its hive rule; `policy.rs` says so at the
   # match site, and the assertion below covers the case that ordering cannot.
   #
@@ -905,11 +905,11 @@ in
             };
             environment = {
               SWARM_AUTHELIA_BRIDGE_BIND = "127.0.0.1:${toString cfg.bridgePort}";
-              # ONE file, and this is it. The bridge used to carry a
-              # second, private `…-users.json` it treated as canonical
-              # while writing `users.yml` as a rendering of it — two
-              # canonical stores for one physical file, which is what
-              # made `swarm agent create` refuse to start on a hive whose
+              # ONE file, and this is it. The bridge keeps no second,
+              # private users store: a store of its own treated as canonical,
+              # with `users.yml` written as a rendering of it, would be two
+              # canonical stores for one physical file, and would make
+              # `swarm agent create` refuse to start on a hive whose
               # `users.yml` already held users.
               SWARM_AUTHELIA_BRIDGE_USERS_FILE = deployCfg.authelia.usersFile;
               # The CONFIGURED authelia, not whatever is on `PATH`: the