fix(app): agent switch should not reset thinking level (#17470)

packages/app/e2e/session/session-model-persistence.spec.ts

@@ -349,3 +349,25 @@ test("session model restore across workspaces", async ({ page, withProject }) =>
     await waitFooter(page, firstState)
   })
 })
+
+test("variant preserved when switching agent modes", async ({ page, withProject }) => {
+  await page.setViewportSize({ width: 1440, height: 900 })
+
+  await withProject(async ({ directory, gotoSession }) => {
+    await gotoSession()
+
+    await ensureVariant(page, directory)
+    const updated = await chooseDifferentVariant(page)
+
+    const available = await agents(page)
+    const other = available.find((name) => name !== updated.agent)
+    test.skip(!other, "only one agent available")
+    if (!other) return
+
+    await choose(page, promptAgentSelector, other)
+    await waitFooter(page, { agent: other, variant: updated.variant })
+
+    await choose(page, promptAgentSelector, updated.agent)
+    await waitFooter(page, { agent: updated.agent, variant: updated.variant })
+  })
+})

packages/app/src/context/local.tsx

@@ -192,10 +192,11 @@ export const { use: useLocal, provider: LocalProvider } = createSimpleContext({
             model: item.model,
             variant: item.variant ?? null,
           })
+          const prev = scope()
           const next = {
             agent: item.name,
-            model: item.model,
-            variant: item.variant,
+            model: item.model ?? prev?.model,
+            variant: item.variant ?? prev?.variant,
           } satisfies State
           const session = id()
           if (session) {