agent: address argus review notes — stale comment + CI typecheck wiring

- StatusChips.tsx: drop the stale 'useAgentState lands in a later
  commit' comment now that Root.tsx already wires it.
- nix/checks.nix: add agent-typecheck, same shape as swarm-ui-typecheck,
  so a real TS error in the agent package fails CI instead of just
  esbuild-stripping silently.

frontend/packages/agent/src/components/StatusChips.tsx

@@ -6,9 +6,9 @@
 // badge here IS the control for what it displays, composed from
 // `@hive/shared`'s `Badge`/`Dropdown` (../../shared/src/badge,
 // ../../shared/src/dropdown). Presentational only: formatting +
-// selection state live in the caller (a `useAgentState` hook lands in a
-// later commit), so this component can be demoed and reviewed against
-// plain sample data before it's wired to `/api/state` polling.
+// selection state live in the caller (`Root.tsx`, via the
+// `useAgentState` hook), so this component can still be demoed and
+// reviewed against plain sample data independent of live `/api/state`.
 import { useState } from 'preact/hooks';
 import { Badge, type BadgeTone } from '@hive/shared/badge.js';
 import { Dropdown, type DropdownOption } from '@hive/shared/dropdown.js';

nix/checks.nix

@@ -175,6 +175,32 @@ in
     '';
   };
 
+  # Same rationale + shape as `swarm-ui-typecheck` above, for the `agent`
+  # package now that its Preact rewrite (hyperhive#3685) has grown enough
+  # real `.tsx`/`.ts` for a type error to matter — argus flagged the same
+  # gap on that PR's review.
+  agent-typecheck = pkgs.buildNpmPackage {
+    pname = "hyperhive-agent-typecheck";
+    version = "0.0.0";
+    src = ../frontend;
+
+    npmDepsHash = builtins.readFile ../frontend/npm-deps-hash;
+
+    buildPhase = ''
+      runHook preBuild
+      npm run typecheck --workspace=packages/agent
+      runHook postBuild
+    '';
+
+    dontNpmInstall = true;
+    installPhase = ''
+      runHook preInstall
+      mkdir -p $out
+      touch $out/ok
+      runHook postInstall
+    '';
+  };
+
   # `hivectl` CLI reference freshness check. The committed
   # markdown at `docs/tools/hivectl-cli.md` is the rendered
   # output of the hidden `hivectl markdown-docs` subcommand