model: runtime override via /model slash; fixes for port + bind

- runtime model override: Bus::{model,set_model} + POST /api/model
  (form-encoded {model: name}). turn.rs reads bus.model() per turn
  so a flip lands on the next claude invocation. /api/state grows
  a model field; agent page shows a 'model · <name>' chip in the
  state row. '/model <name>' slash command POSTs to the endpoint
  and refreshes state.

- port regression fix: agent_web_port no longer probes forward for
  *existing* agents (the previous fix shifted ports for any agent
  without a port file, including legacy ones whose container was
  already bound to the bare hashed port — dashboard rendered the
  new port, container was still on the old one, conn errors). new
  rule: port file exists → use it; absent + applied flake present
  → legacy, persist port_hash without probing; absent + no applied
  flake → fresh spawn, probe forward.

- SO_REUSEADDR on both the dashboard and per-agent web UI binds
  via tokio::net::TcpSocket. operator hit 12 retries failing on
  manager :8000 — REUSEADDR handles the TIME_WAIT case cleanly
  without a new dep; retry still covers the genuine
  process-still-alive overlap.

todo: drops the model-override entry (shipped); adds two new
items — model persistence (optional, future), and custom
per-agent MCP tools (groundwork for moving bitburner-agent into
hyperhive).

hive-ag3nt/assets/app.js

@@ -174,8 +174,31 @@
     { name: '/clear',   desc: 'wipe the terminal panel (local-only)' },
     { name: '/cancel',  desc: 'SIGINT the in-flight claude turn' },
     { name: '/compact', desc: 'compact the persistent claude session' },
+    { name: '/model',   desc: '/model <name>  — switch claude model for future turns' },
   ];
 
+  async function postModel(name) {
+    try {
+      const resp = await fetch('/api/model', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+        body: new URLSearchParams({ model: name }),
+        redirect: 'manual',
+      });
+      const ok = resp.ok || resp.type === 'opaqueredirect'
+        || (resp.status >= 200 && resp.status < 400);
+      if (!ok && termAPI) {
+        const text = await resp.text().catch(() => '');
+        termAPI.row('turn-end-fail', '✗ /model failed: ' + resp.status
+          + (text ? ' — ' + text : ''));
+      } else {
+        refreshState();
+      }
+    } catch (err) {
+      if (termAPI) termAPI.row('turn-end-fail', '✗ /model failed: ' + err);
+    }
+  }
+
   async function postSimple(url, label) {
     try {
       const resp = await fetch(url, { method: 'POST', redirect: 'manual' });
@@ -213,6 +236,16 @@
       case '/compact':
         postCompact();
         return true;
+      case '/model': {
+        const parts = trimmed.split(/\s+/);
+        if (parts.length < 2 || !parts[1]) {
+          termAPI.row('turn-end-fail',
+            '✗ /model needs a name (e.g. /model haiku, /model sonnet, /model opus)');
+        } else {
+          postModel(parts[1]);
+        }
+        return true;
+      }
       default:
         termAPI.row('turn-end-fail', '✗ unknown slash command: ' + cmd + ' — try /help');
         return true;
@@ -365,6 +398,13 @@
       list.append(li);
     }
   }
+  function renderModelChip(model) {
+    const el_ = $('model-chip');
+    if (!el_) return;
+    if (!model) { el_.hidden = true; return; }
+    el_.hidden = false;
+    el_.textContent = 'model · ' + model;
+  }
   function renderLastTurn(ms) {
     const el_ = $('last-turn');
     if (!el_) return;
@@ -424,6 +464,7 @@
       } else if (s.turn_state) {
         setStateAbs(s.turn_state, s.turn_state_since);
       }
+      renderModelChip(s.model);
       // Skip the re-render if nothing structurally changed. The most
       // common case is `online` polling itself — without this guard, the
       // operator's <input value> gets clobbered every cycle.