fix(ui): use sessions row with patched.resolved fallback for model reconciliation

zhangqueping · zhangqueping · commit 7a9980e6897a · 2026-06-30T15:58:41.000+08:00
When a session is absent from the sessions list (new session,
test scenarios), reading only from the sessions row blanks out
the model override.  Prefer the refreshed sessions row for
existing sessions (authoritative post-lifecycle model), fall
back to patched.resolved from the RPC for new sessions, and
finally to nextModel as the ultimate safe default.

Fixes the test regression:
  keeps the selected model visible when the active session
  is absent from sessions.list
diff --git a/ui/src/ui/chat/session-controls.ts b/ui/src/ui/chat/session-controls.ts
@@ -45,7 +45,7 @@ import {
   normalizeThinkLevel,
   resolveThinkingDefaultForModel,
 } from "../thinking.ts";
-import type { FastMode, GatewayThinkingLevelOption, SessionsListResult } from "../types.ts";
+import type { FastMode, GatewayThinkingLevelOption, SessionsListResult, SessionsPatchResult } from "../types.ts";
 
 type ChatSessionSwitchHandler = (state: AppViewState, nextSessionKey: string) => void;
 type ChatSessionSelectSurface = "desktop" | "mobile" | "sidebar";
@@ -1391,36 +1391,34 @@ async function switchChatModel(state: AppViewState, nextModel: string): Promise<
   };
   const switchPromise: Promise<boolean> = (async () => {
     try {
-      await client.request("sessions.patch", {
+      const patched = await client.request<SessionsPatchResult>("sessions.patch", {
         key: targetSessionKey,
         ...scopedAgentParamsForSession(state, targetSessionKey),
         model: nextModel || null,
       });
-      // Refresh the sessions list first so the model-fallback reconciliation
-      // below reads the authoritative server-confirmed model from the session
-      // row.  The server can silently fall back to a different provider (e.g.
-      // when the requested provider is unreachable), and the refreshed row
-      // carries the final effective model after all fallback lifecycle hooks
-      // have run — matching the contract already used by the /model command.
       await refreshSessionOptions(state);
-      // Reconcile the cached override for explicit (non-empty) selections.
-      // When the user picked Default the cache was already set to null above
-      // and must stay null so the selector keeps following the current
-      // default model.
+      // Reconcile the cached override when the user made an explicit (non-empty)
+      // model selection.  `patched.resolved` from the RPC carries the request-time
+      // resolution even before the sessions list is populated.  When the sessions
+      // list already has a row (existing session), prefer the refreshed row
+      // because it carries the final effective model after server-side fallback
+      // lifecycle hooks.  When the row is absent (new session, test scenarios),
+      // fall back to `patched.resolved` so the dropdown still shows the resolved
+      // model rather than getting blanked out.
       if (nextModel) {
         const row = state.sessionsResult?.sessions?.find(
           (s) => s.key === targetSessionKey,
         );
+        const resolvedModel =
+          row?.model ?? patched.resolved?.model ?? nextModel;
+        const resolvedProvider =
+          row?.modelProvider ?? patched.resolved?.modelProvider ?? "";
         const resolvedValue = resolvePreferredServerChatModelValue(
-          row?.model,
-          row?.modelProvider,
+          resolvedModel,
+          resolvedProvider,
           state.chatModelCatalog ?? [],
         );
         const resolvedOverride = createChatModelOverride(resolvedValue);
-        // Only update when the resolved override differs.  This avoids
-        // unnecessary re-renders and preserves the cached override kind
-        // (raw vs qualified) when the server confirms the same model the
-        // user requested — no provider fallback occurred.
         if (
           JSON.stringify(resolvedOverride) !==
           JSON.stringify(state.chatModelOverrides[targetSessionKey])
