Value opencode Go plan requests; per-duration cache prices; usage under answers

- opencode Go reports plan requests as cost 0 with the usage in allowance;
  ModelConfig::cost values them at the model's list prices (charged amounts
  and free requests stay as reported). Rows booked at 0 are valued once on
  start (idempotent).
- opencode's price list now has per-duration cache prices for some models
  ({"30m": ..., "12h": ...}): the shortest duration is used, also in tiers.
  Saving the provider's models failed with "untagged enum ModelEntry".
- Each answer shows tokens sent/received and the cost of the turn's requests
  (usage.cost filled when messages are saved and loaded).
- The chat title keeps a minimum width in a crowded top bar.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/components/ChatView.tsx

@@ -245,8 +245,10 @@ const MessageList = memo(function MessageList({
   baseDir,
   onRewind,
   highlight,
+  currency,
 }: {
   messages: Message[];
+  currency: string;
   results: Map<string, ToolResult>;
   busy: boolean;
   canEdit: boolean;
@@ -280,13 +282,52 @@ const MessageList = memo(function MessageList({
         ));
         // Finished turns with tool steps fold into one line (the answer stays visible).
         const steps = b.messages.flatMap((m) => m.parts.filter((p) => p.type === "tool_call")) as ToolCall[];
-        if (i === lastWork || steps.length < 2) return <div key={key}>{items}</div>;
-        return <WorkBlock key={key} messages={b.messages} steps={steps} open={!!highlight && b.messages.some((m) => m.id === highlight)} baseDir={baseDir}>{items}</WorkBlock>;
+        const usage = !(busy && i === lastWork) && <TurnUsage messages={b.messages} currency={currency} />;
+        if (i === lastWork || steps.length < 2)
+          return (
+            <div key={key}>
+              {items}
+              {usage}
+            </div>
+          );
+        return (
+          <div key={key}>
+            <WorkBlock messages={b.messages} steps={steps} open={!!highlight && b.messages.some((m) => m.id === highlight)} baseDir={baseDir}>
+              {items}
+            </WorkBlock>
+            {usage}
+          </div>
+        );
       })}
     </>
   );
 });
 
+/** Tokens (in/out) and cost of one answer: all requests of the turn together. */
+function TurnUsage({ messages, currency }: { messages: Message[]; currency: string }) {
+  const t = useT();
+  let inp = 0;
+  let out = 0;
+  let cost = 0;
+  let requests = 0;
+  for (const m of messages) {
+    const u = m.role === "assistant" ? m.usage : undefined;
+    if (!u) continue;
+    requests++;
+    inp += u.input_tokens + u.cache_read_tokens + u.cache_write_tokens;
+    out += u.output_tokens;
+    cost += u.cost ?? 0;
+  }
+  if (!requests) return null;
+  return (
+    <div className="turn-usage" title={t("chat.turnUsageHint", { n: requests })}>
+      {fmtCompact(inp)}
+      <Icon name="arrow-up" className="tiny" /> {fmtCompact(out)}
+      <Icon name="arrow-down" className="tiny" /> · {fmtCost(cost, currency)}
+    </div>
+  );
+}
+
 /** A finished turn: "42 steps · 3 files" and the answer; the steps on click. */
 function WorkBlock({ messages, steps, open: forced, baseDir, children }: { messages: Message[]; steps: ToolCall[]; open: boolean; baseDir: string; children: ReactNode }) {
   const t = useT();
@@ -825,6 +866,7 @@ export function ChatView({ sessionId, onMenu, onClosePane }: { sessionId: string
             baseDir={session.cwd}
             onRewind={onRewind}
             highlight={highlight}
+            currency={stats?.currency ?? "USD"}
           />
           {win?.newer && (
             <button className="back-to-latest" onClick={() => void showLatest()}>