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>

server/src/api.rs

@@ -843,6 +843,19 @@ impl WindowQ {
     }
 }
 
+/// The cost of each answer for the chat view (usage.cost: charged, or valued at list prices).
+fn with_costs(app: &App, mut messages: Vec<crate::types::Message>) -> Vec<crate::types::Message> {
+    let registry = app.registry();
+    for m in &mut messages {
+        if let (Some(u), Some(spec)) = (m.usage.as_mut(), m.model.as_deref()) {
+            if let Ok((_, model)) = registry.resolve(spec) {
+                u.cost = Some(model.cost(u));
+            }
+        }
+    }
+    messages
+}
+
 async fn get_session(Extension(user): Extension<User>, State(app): State<AppState>, Path(id): Path<String>, Query(q): Query<WindowQ>) -> ApiResult {
     let s = readable(&app, &user, &id)?;
     let busy = app.is_busy(&id);
@@ -853,7 +866,7 @@ async fn get_session(Extension(user): Extension<User>, State(app): State<AppStat
     match q.window() {
         Some(w) => {
             let (messages, older, newer) = app.store.messages_window(&id, &w)?;
-            out["messages"] = json!(messages);
+            out["messages"] = json!(with_costs(&app, messages));
             out["has_older"] = json!(older);
             out["has_newer"] = json!(newer);
         }
@@ -867,7 +880,7 @@ async fn session_messages(Extension(user): Extension<User>, State(app): State<Ap
     readable(&app, &user, &id)?;
     let w = q.window().ok_or_else(|| ApiError(StatusCode::BAD_REQUEST, "before, after, around or limit is required".into()))?;
     let (messages, older, newer) = app.store.messages_window(&id, &w).map_err(|e| ApiError(StatusCode::NOT_FOUND, format!("{e:#}")))?;
-    Ok(Json(json!({"messages": messages, "has_older": older, "has_newer": newer})))
+    Ok(Json(json!({"messages": with_costs(&app, messages), "has_older": older, "has_newer": newer})))
 }
 
 /// Images, videos and audio files shown in a chat (all of it, with subagents).