refactor(frontend): extract the agent roster into dashboard/state.js (#1451)

First step of splitting the 4.3k-line tabs.js monolith into per-tab
modules. The live agent roster (containersState) is the one piece of
genuinely cross-domain state — read by the container tree, the
capabilities + tool-group matrices, the schedule target-chips, the
container-load poll, the selection bar and the operator inbox. Move it
(and its snapshot-sync) into a new dashboard/state.js that each domain
module imports, so the upcoming per-tab extractions have a single source
of truth to depend on instead of a shared IIFE closure.

Minimal by design — only the roster moves; the container row cache and
the apply-handlers (which also re-render) stay with the container domain.
Behaviour-preserving: the imported Map is mutated in place exactly as
before. esbuild inlines state.js into the existing tabs.js bundle, so the
static output is unchanged. Build green.

frontend/packages/dashboard/src/state.js

@@ -0,0 +1,25 @@
+// Shared dashboard state — the one piece of cross-domain state in the
+// dashboard SPA: the live agent roster.
+//
+// The roster is read by nearly every tab (the container tree, the
+// capabilities + tool-group matrices, the schedule target-chips, the
+// container-load poll, the selection bar, and the operator inbox), so
+// it lives here as a single source of truth that each domain module
+// imports rather than threading through call signatures. Everything
+// else in the dashboard is domain-local and lives with its own module.
+//
+// `containersState` is keyed by `ContainerView.name` so a lifecycle
+// form's POST → 200 → matching SSE event can flip a single row without
+// a full snapshot refetch. Mutated in place (`set` / `delete` / `clear`)
+// by the container apply-handlers; consumers read it by reference, so
+// the imported binding always reflects the latest roster.
+
+export const containersState = new Map();
+
+// Replace the whole roster from a fresh `/api/state` snapshot. Called by
+// the entry's `refreshState` on cold load and after async-form submits;
+// live single-row updates go through the container apply-handlers.
+export function syncContainersFromSnapshot(s) {
+  containersState.clear();
+  for (const c of s.containers || []) containersState.set(c.name, c);
+}

frontend/packages/dashboard/src/tabs.js

@@ -19,6 +19,7 @@ import {
   openStream, renderServerWarnings,
 } from './common.js';
 import { createTabStrip } from '@hive/shared/tabs.js';
+import { containersState, syncContainersFromSnapshot } from './state.js';
 
 // mdNode (in common.js) reads `window.marked` for the markdown side
 // panel preview path. Set it here on the dashboard entry so file
@@ -149,23 +150,18 @@ window.marked = marked;
     }
   });
 
-  // Derived container state — cold-loaded from /api/state.containers,
-  // then mutated live by `container_state_changed` (upsert by name)
-  // and `container_removed` (drop by name). The coordinator's rescan
-  // helper fires these after every mutation site + on a periodic poll
-  // in crash_watch. Keyed by ContainerView.name so the lifecycle
-  // forms' POST → 200 → matching event flips the row without a
-  // snapshot refetch.
-  const containersState = new Map();
+  // The live agent roster (`containersState`) + its snapshot-sync now
+  // live in `./state.js` — it's the one piece of cross-domain state, read
+  // by nearly every tab. It's still mutated live by `container_state_changed`
+  // (upsert by name) and `container_removed` (drop by name) via the apply
+  // handlers just below; the imported binding reflects those in place.
+  //
   // Keyed container row cache. Maps agent name → { el: <li>, fingerprint }.
   // Allows renderContainers to skip rebuilding rows whose displayed state
   // hasn't changed — prevents full-wipe flicker + avoids redundant async
-  // dashboard-state fetches on every SSE event.
+  // dashboard-state fetches on every SSE event. Container-domain only,
+  // so it stays here (not in state.js).
   const containerRowCache = new Map();
-  function syncContainersFromSnapshot(s) {
-    containersState.clear();
-    for (const c of s.containers || []) containersState.set(c.name, c);
-  }
   function applyContainerStateChanged(ev) {
     if (!ev.container || !ev.container.name) return;
     containersState.set(ev.container.name, ev.container);