agent ui: event-driven status / model / token_usage / turn_state

new LiveEvent variants on the per-agent bus —
status_changed / model_changed / token_usage_changed /
turn_state_changed — replace the per-agent web UI's
/api/state polling for the badge row.

emit sites:
- Bus::set_model → model_changed
- Bus::record_usage → token_usage_changed
- Bus::set_state → turn_state_changed
- turn::wait_for_login → status_changed("online") on creds detect
- post_login_start / post_login_cancel → status_changed("needs_login_*")

per-agent endpoints (post_set_model / post_compact / post_new_session
/ post_cancel_turn / post_login_*) now all return 200; client
drops the post-submit refetch except on login transitions, which
still need /api/state to render the OAuth form + session stream.

client adds dispatch on the four new event kinds, threads
`currentLabel` through so the composer re-enables on a live
status flip, and no longer fires refreshState() from turn_end or
postModel — the events carry the same signal faster.

closes the per-agent half of the dashboard event-channel
refactor; TODO entry dropped.

hive-ag3nt/assets/app.js

@@ -168,6 +168,10 @@
   // dispatcher to print local-only rows ('help', errors) and to clear
   // the terminal on `/clear`.
   let termAPI = null;
+  // Label captured from the first /api/state cold load — used by the
+  // bus-driven `status_changed` handler so it can re-enable the
+  // composer without waiting for the next snapshot fetch.
+  let currentLabel = '';
 
   const SLASH_COMMANDS = [
     { name: '/help',        desc: 'list slash commands' },
@@ -192,9 +196,9 @@
         const text = await resp.text().catch(() => '');
         termAPI.row('turn-end-fail', '✗ /model failed: ' + resp.status
           + (text ? ' — ' + text : ''));
-      } else {
-        refreshState();
       }
+      // No refreshState — the harness emits `model_changed` on the
+      // SSE bus and the chip handler picks it up live.
     } catch (err) {
       if (termAPI) termAPI.row('turn-end-fail', '✗ /model failed: ' + err);
     }
@@ -523,6 +527,7 @@
       if (!resp.ok) throw new Error('http ' + resp.status);
       const s = await resp.json();
       if (!headerSet) { setHeader(s.label, s.dashboard_port); headerSet = true; }
+      currentLabel = s.label;
       renderTermInput(s.label, s.status === 'online');
       renderInbox(s.inbox || []);
       // Authoritative state comes from the harness via /api/state.
@@ -725,8 +730,6 @@
             openTurnsFromHistory = Math.max(0, openTurnsFromHistory - 1);
           } else {
             setBannerActive(false); setState('idle');
-            // Login may have just landed (or session re-enters Online).
-            refreshState();
           }
           const cls = ev.ok ? 'turn-end-ok' : 'turn-end-fail';
           api.row(cls,
@@ -738,6 +741,38 @@
           const v = Object.assign({}, ev); delete v.kind;
           renderStream(v, api);
         },
+        // Bus-driven state/badges. `status_changed` may also need a
+        // /api/state refresh to render the login `#status` block
+        // (which carries the OAuth URL + form), so we kick the
+        // existing refresh path on that transition. Online → only
+        // the badge updates; no /api/state fetch needed.
+        status_changed(ev, api) {
+          if (api.fromHistory) return;
+          renderAliveBadge(ev.status);
+          renderTermInput(currentLabel, ev.status === 'online');
+          // Login-flow transitions need the #status block rebuilt
+          // (it carries the OAuth URL + form). The existing
+          // refreshState path also re-arms the in-progress poll for
+          // session output streaming. Online → only the badge moves;
+          // no /api/state fetch is necessary.
+          if (ev.status !== 'online' && ev.status !== lastStatus) {
+            refreshState();
+          } else if (ev.status === 'online' && lastStatus !== 'online') {
+            // Status block stays as-is or shows the previous
+            // login UI; clear it so the operator sees a clean
+            // online state without a separate refetch.
+            const root = $('status');
+            if (root) root.innerHTML = '';
+            lastStatus = 'online';
+          }
+        },
+        model_changed(ev, api) { if (!api.fromHistory) renderModelChip(ev.model); },
+        token_usage_changed(ev, api) {
+          if (!api.fromHistory) renderTokenUsage(ev.usage);
+        },
+        turn_state_changed(ev, api) {
+          if (!api.fromHistory) setStateAbs(ev.state, ev.since_unix);
+        },
       },
       onBackfillDone() {
         // If the last replayed turn never closed, the banner shimmer +