types: let nix own the reserved-name blacklist

One list, in nix/reserved-names.nix, handed to everything that needs it
as HIVE_RESERVED_NAMES. Keeping it current becomes a config change
rather than a rebuild, and hive names and agent names -- one namespace
going forward -- are checked against the same file: swarm-otel.nix's
hand-written reservedOwners is gone.

Whitespace-separated rather than JSON, deliberately, unlike the
structured env vars beside it. Every entry is an Ident ([a-z0-9-]), so
whitespace cannot occur inside a name and the encoding is provably
lossless; JSON would mean either a parser dependency in a crate whose
purpose is to have none, or a copy of the parse in every consumer.

An UNSET variable is not "nothing is reserved". Both creation sites log
an error and return a warning saying the check did not run, so a
misconfigured deployment says so instead of silently accepting every
name. A blank value folds into unset: nix always renders a non-empty
list, so present-but-empty is a rendering fault, not a declaration.

Two guards whose subject moved out of their own file now assert their
own case is still in it, because a guard that can be retired by an edit
elsewhere is not a guard:

- swarm-otel.nix asserts reserved-names.nix still contains its
  swarmTierName.
- hive-sh4re's sentinel drift test PANICS when the variable is missing
  rather than skipping -- a drift test that quietly does nothing still
  reports green. checks.nix and devshell.nix both export it so CI and a
  local cargo test agree. Verified as a pair: with the variable set, 8
  tests pass; with it unset, exactly the 4 drift tests fail and the
  unrelated ones still pass.

nix/reserved-names.nix

@@ -0,0 +1,67 @@
+# The one blacklist: names no agent and no hive may take.
+#
+# Nix owns this list and hands it to the Rust side as an environment variable
+# (`HIVE_RESERVED_NAMES`), so keeping it current is a config change rather than
+# a rebuild of a binary. Read by:
+#
+#   - `host-modules/hive-c0re/environment.nix`  -> the env var, for the
+#     `request_init_config` path every hive uses
+#   - `host-modules/swarm-controller.nix`       -> the same var, for the
+#     swarm-level `create_agent` path
+#   - `host-modules/swarm-otel.nix`             -> its `<owner>` assertion, so
+#     a hive name and an agent name are checked against ONE list
+#   - `nix/checks.nix`                          -> exported into `cargo test`,
+#     which is what keeps the message layer's sentinels from drifting away
+#     from this file
+#
+# A plain nix file rather than a module option because two of those readers are
+# flake-level (`checks.nix`) and cannot see a NixOS option.
+#
+# ⚠️ Agent names and hive names are ONE namespace going forward (mara, 2026-08-27:
+# "agent and hive names live in the swarm level going forward"). Adding a name
+# here forbids it for both. That is the point: two lists is how they drift.
+#
+# ⚠️ Every entry must be a value some component actually PRODUCES as a message
+# `from`/`to`, or a component name the collector builds pipelines from — not a
+# word that merely looked risky. A name in here that nothing emits is a refusal
+# with no failure behind it.
+[
+  # ---- message-layer senders -------------------------------------------
+  # The human at the dashboard: a broker recipient (the T4LK box sends
+  # `{from: "operator", ...}`) and the fallback attribution for an answered
+  # question.
+  "operator"
+  # Helper events (`approval_resolved`, `container_crash`, ...) — the sender an
+  # agent is told to treat as hyperhive itself rather than as a peer.
+  # `hive_sh4re::manager::SYSTEM_SENDER`.
+  "system"
+  # A due self-scheduled reminder arrives as its own sender, so a wake I asked
+  # for last week is distinguishable from a peer message.
+  "reminder"
+  # Forge notification wakes, delivered by the notify daemon.
+  "forge"
+  # A scheduled prompt firing, pushed as a trusted sender.
+  "scheduled"
+  # Three synthetic wakes the harness itself produces: an in-container todo,
+  # the follow-up turn after a self-requested compaction, and the single flush
+  # turn before a graceful stop.
+  "todo"
+  "compact"
+  "graceful-stop"
+
+  # ---- swarm-tier component owners -------------------------------------
+  # The swarm collector names its components `<kind>/<owner>` and uses the hive
+  # name as the owner, so a hive called `swarm` would silently replace the
+  # swarm tier's own pipelines and lose its own — it would keep accepting
+  # pushes into a pipeline that routes nowhere. Previously enforced only
+  # against hive names, in `swarm-otel.nix`'s own `reservedOwners`.
+  "swarm"
+]
+# Deliberately absent, and both are load-bearing omissions:
+#
+#   `<parent>` / `<children>` — routing recipients the ident charset already
+#   rejects, so no name can ever equal them; listing them would imply a guard
+#   that never fires.
+#
+#   `ruth` — a real agent, not a literal. A second agent wanting that name is a
+#   name that is TAKEN, which the roster answers, not this list.