fix(app): new session uses agent model/variant

2 files changed, 91 insertions, 1 deletions

diff --git a/packages/app/src/pages/session/session-model-helpers.test.ts b/packages/app/src/pages/session/session-model-helpers.test.ts
index ae8700ccd..5f554dcd3 100644
--- a/packages/app/src/pages/session/session-model-helpers.test.ts
+++ b/packages/app/src/pages/session/session-model-helpers.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from "bun:test"
 import type { UserMessage } from "@opencode-ai/sdk/v2"
-import { syncSessionModel } from "./session-model-helpers"
+import { resetSessionModel, syncSessionModel } from "./session-model-helpers"
 
 const message = (input?: Partial<Pick<UserMessage, "agent" | "model" | "variant">>) =>
   ({
@@ -20,6 +20,9 @@ describe("syncSessionModel", () => {
     syncSessionModel(
       {
         agent: {
+          current() {
+            return undefined
+          },
           set(value) {
             calls.push(["agent", value])
           },
@@ -54,6 +57,9 @@ describe("syncSessionModel", () => {
     syncSessionModel(
       {
         agent: {
+          current() {
+            return undefined
+          },
           set(value) {
             calls.push(["agent", value])
           },
@@ -81,3 +87,72 @@ describe("syncSessionModel", () => {
     ])
   })
 })
+
+describe("resetSessionModel", () => {
+  test("restores the current agent defaults", () => {
+    const calls: unknown[] = []
+
+    resetSessionModel({
+      agent: {
+        current() {
+          return {
+            model: { providerID: "anthropic", modelID: "claude-sonnet-4" },
+            variant: "high",
+          }
+        },
+        set() {},
+      },
+      model: {
+        set(value) {
+          calls.push(["model", value])
+        },
+        current() {
+          return undefined
+        },
+        variant: {
+          set(value) {
+            calls.push(["variant", value])
+          },
+        },
+      },
+    })
+
+    expect(calls).toEqual([
+      ["model", { providerID: "anthropic", modelID: "claude-sonnet-4" }],
+      ["variant", "high"],
+    ])
+  })
+
+  test("clears the variant when the agent has none", () => {
+    const calls: unknown[] = []
+
+    resetSessionModel({
+      agent: {
+        current() {
+          return {
+            model: { providerID: "anthropic", modelID: "claude-sonnet-4" },
+          }
+        },
+        set() {},
+      },
+      model: {
+        set(value) {
+          calls.push(["model", value])
+        },
+        current() {
+          return undefined
+        },
+        variant: {
+          set(value) {
+            calls.push(["variant", value])
+          },
+        },
+      },
+    })
+
+    expect(calls).toEqual([
+      ["model", { providerID: "anthropic", modelID: "claude-sonnet-4" }],
+      ["variant", undefined],
+    ])
+  })
+})
diff --git a/packages/app/src/pages/session/session-model-helpers.ts b/packages/app/src/pages/session/session-model-helpers.ts
index ab181df59..7600f16d5 100644
--- a/packages/app/src/pages/session/session-model-helpers.ts
+++ b/packages/app/src/pages/session/session-model-helpers.ts
@@ -3,6 +3,12 @@ import { batch } from "solid-js"
 
 type Local = {
   agent: {
+    current():
+      | {
+          model?: UserMessage["model"]
+          variant?: string
+        }
+      | undefined
     set(name: string | undefined): void
   }
   model: {
@@ -19,6 +25,15 @@ type Local = {
   }
 }
 
+export const resetSessionModel = (local: Local) => {
+  const agent = local.agent.current()
+  if (!agent) return
+  batch(() => {
+    local.model.set(agent.model)
+    local.model.variant.set(agent.variant)
+  })
+}
+
 export const syncSessionModel = (local: Local, msg: UserMessage) => {
   batch(() => {
     local.agent.set(msg.agent)