fix(tui): distinguish variant switch notices (#35315)

packages/tui/src/context/data.tsx

@@ -235,6 +235,7 @@ export const { use: useData, provider: DataProvider } = createSimpleContext({
         case "session.model.selected":
           if (store.session.info[event.data.sessionID])
             setStore("session", "info", event.data.sessionID, "model", event.data.model)
+          if (!store.session.message[event.data.sessionID]) break
           message.update(event.data.sessionID, (draft, index) => {
             message.append(draft, index, {
               id: messageIDFromEvent(event.id),
@@ -243,6 +244,16 @@ export const { use: useData, provider: DataProvider } = createSimpleContext({
               time: { created: event.created },
             })
           })
+          void sdk.api.session
+            .message({ sessionID: event.data.sessionID, messageID: messageIDFromEvent(event.id) })
+            .then((item) => {
+              message.update(event.data.sessionID, (draft, index) => {
+                const position = index.get(item.id)
+                if (position === undefined) return message.append(draft, index, mutable(item))
+                draft[position] = mutable(item)
+              })
+            })
+            .catch((error) => console.error("Failed to load projected model switch message", error))
           break
         case "session.renamed":
           if (store.session.info[event.data.sessionID])

packages/tui/src/routes/session/index.tsx

@@ -1231,7 +1231,8 @@ function SessionSwitchMessageV2(props: { message: SessionMessage }) {
   const { theme } = useTheme()
   const text = () => {
     if (props.message.type === "agent-switched") return `Switched agent to ${props.message.agent}`
-    if (props.message.type === "model-switched") return switchLabel(props.message.model, ctx.models())
+    if (props.message.type === "model-switched")
+      return switchLabel(props.message.model, ctx.models(), props.message.previous)
     return ""
   }
   return <text fg={theme.textMuted}>{text()}</text>

packages/tui/src/util/model.ts

@@ -34,11 +34,12 @@ export function formatRef(model: { providerID: string; id: string; variant?: str
 export function switchLabel(
   model: { providerID: string; id: string; variant?: string },
   models?: readonly { providerID: string; id: string; name: string }[],
+  previous?: { providerID: string; id: string; variant?: string },
 ) {
+  if (previous?.providerID === model.providerID && previous.id === model.id)
+    return `Switched variant to ${model.variant ?? "default"}`
   const display = models?.find((item) => item.providerID === model.providerID && item.id === model.id)?.name
   if (display === undefined) return `Switched model to ${formatRef(model)}`
-  // Variant-only switches publish the same model id; without the variant the
-  // notice would look like a redundant model switch.
   const variant = model.variant && model.variant !== "default" ? ` (${model.variant})` : ""
   return `Switched model to ${display}${variant}`
 }

packages/tui/test/cli/tui/data.test.tsx

@@ -767,7 +767,18 @@ test("adds and dismisses question requests from live events", async () => {
 
 test("settles pending tools when a live failure arrives", async () => {
   const events = createEventStream()
-  const calls = createFetch(undefined, events)
+  const calls = createFetch((url) => {
+    if (url.pathname === "/api/session/session-1/message/msg_model_1")
+      return json({
+        data: {
+          id: "msg_model_1",
+          type: "model-switched",
+          previous: { id: "model-1", providerID: "provider-1", variant: "medium" },
+          model: { id: "model-1", providerID: "provider-1", variant: "high" },
+          time: { created: 0 },
+        },
+      })
+  }, events)
   let sync!: ReturnType<typeof useData>
   let ready!: () => void
   const mounted = new Promise<void>((resolve) => {
@@ -808,7 +819,7 @@ test("settles pending tools when a live failure arrives", async () => {
       durable: durable("session-1", 1),
       data: {
         sessionID: "session-1",
-        model: { id: "model-1", providerID: "provider-1" },
+        model: { id: "model-1", providerID: "provider-1", variant: "high" },
       },
     })
     emitEvent(events, {
@@ -895,6 +906,11 @@ test("settles pending tools when a live failure arrives", async () => {
       "model-switched",
       "assistant",
     ])
+    expect(sync.session.message.get("session-1", "msg_model_1")).toMatchObject({
+      type: "model-switched",
+      previous: { id: "model-1", providerID: "provider-1", variant: "medium" },
+      model: { id: "model-1", providerID: "provider-1", variant: "high" },
+    })
   } finally {
     app.renderer.destroy()
   }

packages/tui/test/util/model.test.ts

@@ -34,4 +34,16 @@ describe("util.model", () => {
       "Switched model to removed/gone/high",
     )
   })
+
+  test("distinguishes variant-only switches from model switches", () => {
+    const previous = { providerID: "openai", id: "gpt-5.5", variant: "medium" }
+
+    expect(switchLabel({ ...previous, variant: "high" }, undefined, previous)).toBe("Switched variant to high")
+    expect(switchLabel({ providerID: "openai", id: "gpt-5.5" }, undefined, previous)).toBe(
+      "Switched variant to default",
+    )
+    expect(switchLabel({ providerID: "anthropic", id: "sonnet", variant: "high" }, undefined, previous)).toBe(
+      "Switched model to anthropic/sonnet/high",
+    )
+  })
 })