agent page: show resolved model as the model badge's tooltip

mara: 'i cannot see if sonnet became claude-sonnet-5 or something
else.' /api/state now carries resolved_model (bus.last_resolved_model(),
already used by serve_common.rs's turn-stats rollup for the same
alias-vs-actual reason) and the model badge shows it as a title
tooltip, same pattern as the ctx/cost badges.

frontend/packages/agent/src/Root.tsx

@@ -192,6 +192,7 @@ export function Root() {
           stateTone={turnDef.tone}
           stateTooltip={STATE_TOOLTIPS[effectiveTurnState]}
           model={state.model}
+          resolvedModel={state.resolved_model ?? undefined}
           availableModels={state.available_models}
           onSelectModel={(name) => {
             postModel(name).then(() => refresh());

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

@@ -21,6 +21,11 @@ export interface StatusChipsProps {
   stateTone: BadgeTone;
   stateTooltip?: string;
   model: string;
+  /** Concrete model id the last completed turn actually ran on, e.g.
+   * "claude-sonnet-4-5-20260805" — shown as the badge's tooltip so the
+   * operator can tell what an alias resolved to. `undefined` before any
+   * turn has completed. */
+  resolvedModel?: string;
   availableModels: string[];
   onSelectModel: (name: string) => void;
   effort: string;
@@ -54,12 +59,14 @@ function Picker({
   options,
   descriptions,
   onSelect,
+  title,
 }: {
   label: string;
   value: string;
   options: string[];
   descriptions: Record<string, string>;
   onSelect: (v: string) => void;
+  title?: string;
 }) {
   const [open, setOpen] = useState(false);
   const dropdownOptions: DropdownOption[] = options.map((name) => ({
@@ -69,7 +76,7 @@ function Picker({
   }));
   return (
     <div class="status-chip-anchor">
-      <Badge label={label} value={value} onClick={() => setOpen((o) => !o)} expanded={open} />
+      <Badge label={label} value={value} onClick={() => setOpen((o) => !o)} expanded={open} title={title} />
       <Dropdown
         open={open}
         options={dropdownOptions}
@@ -92,6 +99,7 @@ export function StatusChips({
   stateTone,
   stateTooltip,
   model,
+  resolvedModel,
   availableModels,
   onSelectModel,
   effort,
@@ -123,6 +131,7 @@ export function StatusChips({
         options={availableModels}
         descriptions={MODEL_DESCRIPTIONS}
         onSelect={onSelectModel}
+        title={resolvedModel ? `resolved to ${resolvedModel}` : undefined}
       />
       {availableEfforts.length ? (
         <Picker

frontend/packages/agent/src/types.ts

@@ -14,6 +14,7 @@ export interface AgentState {
   turn_state: string;
   turn_state_since: number;
   model: string;
+  resolved_model: string | null;
   context_window_tokens: number;
   ctx_usage: TokenUsage | null;
   cost_usage: TokenUsage | null;