feat(agent): read available models from HIVE_AVAILABLE_MODELS env var

web_ui.rs: add available_models() helper that reads HIVE_AVAILABLE_MODELS
(comma-separated, injected by services.hyperhive.availableModels nix option).
Falls back to ["haiku", "sonnet", "opus"] when absent or empty. Field added
to StateSnapshot so the frontend receives the list on cold-load.

app.js: replace hardcoded MODEL_ALIASES array with availableModels module var.
Seeded from state.available_models before setHeader/populateOverflowMenu on
first /api/state load. Well-known aliases (haiku/sonnet/opus) still get their
descriptive labels; operator-declared custom model names show the name itself.

Implements the frontend + web_ui.rs side of issue #1359 (nix option shipped
separately in PR #1360 by atlas).

frontend/packages/agent/src/app.js

@@ -273,33 +273,37 @@ window.marked = marked;
     menu.append(logoutBtn);
 
     // ─── model quick-picker ────────────────────────────────────────
-    // Three one-click shortcuts for the most common model aliases.
+    // One-click shortcuts for each model in `availableModels` (seeded
+    // from `state.available_models` / `HIVE_AVAILABLE_MODELS` nix option).
     // The active model is highlighted via the `active` class; see
     // `renderModelChip` which updates `modelPickerBtns` live.
     const modelSep = el('div', { class: 'overflow-sep', 'aria-hidden': 'true' });
     const modelLabel = el('div', { class: 'overflow-section-label' }, 'model');
     menu.append(modelSep, modelLabel);
-    const MODEL_ALIASES = [
-      { name: 'haiku',  label: 'haiku   (fast)' },
-      { name: 'sonnet', label: 'sonnet  (balanced)' },
-      { name: 'opus',   label: 'opus    (powerful)' },
-    ];
+    // Well-known aliases get a parenthetical description; unknown aliases
+    // (operator-declared custom models) show just the name.
+    const MODEL_DESCRIPTIONS = {
+      haiku:  'haiku   (fast)',
+      sonnet: 'sonnet  (balanced)',
+      opus:   'opus    (powerful)',
+    };
     modelPickerBtns = [];
-    for (const m of MODEL_ALIASES) {
+    for (const name of availableModels) {
+      const label = MODEL_DESCRIPTIONS[name] ?? name;
       const btn = el('button', {
         type: 'button',
         class: 'overflow-item overflow-item-model',
         role: 'menuitem',
-        title: `/model ${m.name}`,
-        'data-model': m.name,
+        title: `/model ${name}`,
+        'data-model': name,
       },
         el('span', { class: 'overflow-item-icon', 'aria-hidden': 'true' }, '⊞'),
-        m.label,
+        label,
       );
       btn.addEventListener('click', () => {
-        if (currentModel === m.name) { closeOverflowMenu(); return; }
+        if (currentModel === name) { closeOverflowMenu(); return; }
         closeOverflowMenu();
-        postModel(m.name);
+        postModel(name);
       });
       modelPickerBtns.push(btn);
       menu.append(btn);
@@ -471,6 +475,10 @@ window.marked = marked;
   // menu so renderModelChip can update their `active` state without
   // rebuilding the whole menu.
   let modelPickerBtns = [];
+  // Ordered list of model short-names available on this hive. Seeded from
+  // `state.available_models` (injected by the nix option); falls back to
+  // the built-in default until the first /api/state cold-load completes.
+  let availableModels = ['haiku', 'sonnet', 'opus'];
 
   const SLASH_COMMANDS = [
     { name: '/help',        desc: 'list slash commands' },
@@ -1113,6 +1121,12 @@ window.marked = marked;
       const resp = await fetch('api/state');
       if (!resp.ok) throw new Error('http ' + resp.status);
       const s = await resp.json();
+      // Seed available_models before populateOverflowMenu (called from
+      // setHeader on the first load) so the picker uses the operator-declared
+      // list rather than the JS fallback default.
+      if (Array.isArray(s.available_models) && s.available_models.length > 0) {
+        availableModels = s.available_models;
+      }
       if (!headerSet) { setHeader(s.label, s.qualified_label, s.dashboard_port, s.hive_name, s.swarm_name); headerSet = true; }
       currentLabel = s.label;
       // Render server-supplied navigation links — see

hive-ag3nt/src/web_ui.rs

@@ -436,6 +436,14 @@ struct StateSnapshot {
     /// Human name of the swarm (e.g. `"constellat1on"`). Sourced from
     /// `HYPERHIVE_SWARM_NAME`; `None` when unset.
     swarm_name: Option<String>,
+    /// Ordered list of model short-names the operator has declared as
+    /// available on this hive. Sourced from `HIVE_AVAILABLE_MODELS`
+    /// (comma-separated, set by `services.hyperhive.availableModels`).
+    /// Falls back to `["haiku", "sonnet", "opus"]` when the env var is
+    /// absent or empty. The frontend model quick-picker renders one button
+    /// per entry in this list, so operators can add new models or drop
+    /// ones they don't want without touching the frontend code.
+    available_models: Vec<String>,
 }
 
 /// One navigation link in the agent page header row. The same JSON
@@ -561,6 +569,7 @@ async fn api_state(State(state): State<AppState>) -> axum::Json<StateSnapshot> {
             .filter(|s| !s.is_empty()),
         hive_name: crate::identity::hive_name(),
         swarm_name: crate::identity::swarm_name(),
+        available_models: available_models(),
     })
 }
 
@@ -1076,3 +1085,25 @@ fn error_response(message: &str) -> Response {
     // be noise.
     (StatusCode::INTERNAL_SERVER_ERROR, message.to_owned()).into_response()
 }
+
+/// Read `HIVE_AVAILABLE_MODELS` (comma-separated short names injected by
+/// `services.hyperhive.availableModels`) and return the parsed list.
+/// Falls back to `["haiku", "sonnet", "opus"]` when the env var is absent
+/// or resolves to an empty list after trimming.
+fn available_models() -> Vec<String> {
+    const DEFAULT: &[&str] = &["haiku", "sonnet", "opus"];
+    let raw = match std::env::var("HIVE_AVAILABLE_MODELS") {
+        Ok(v) if !v.trim().is_empty() => v,
+        _ => return DEFAULT.iter().map(|s| s.to_string()).collect(),
+    };
+    let models: Vec<String> = raw
+        .split(',')
+        .map(|s| s.trim().to_string())
+        .filter(|s| !s.is_empty())
+        .collect();
+    if models.is_empty() {
+        DEFAULT.iter().map(|s| s.to_string()).collect()
+    } else {
+        models
+    }
+}