fix(app): model sticks to session

6 files changed, 176 insertions, 8 deletions

diff --git a/packages/app/src/components/prompt-input/submit.test.ts b/packages/app/src/components/prompt-input/submit.test.ts
index c633525a2..4109417d2 100644
--- a/packages/app/src/components/prompt-input/submit.test.ts
+++ b/packages/app/src/components/prompt-input/submit.test.ts
@@ -6,10 +6,19 @@ let createPromptSubmit: typeof import("./submit").createPromptSubmit
 const createdClients: string[] = []
 const createdSessions: string[] = []
 const enabledAutoAccept: Array<{ sessionID: string; directory: string }> = []
+const optimistic: Array<{
+  message: {
+    agent: string
+    model: { providerID: string; modelID: string }
+    variant?: string
+  }
+}> = []
 const sentShell: string[] = []
 const syncedDirectories: string[] = []
 
+let params: { id?: string } = {}
 let selected = "/repo/worktree-a"
+let variant: string | undefined
 
 const promptValue: Prompt = [{ type: "text", content: "ls", start: 0, end: 2 }]
 
@@ -26,6 +35,7 @@ const clientFor = (directory: string) => {
         return { data: undefined }
       },
       prompt: async () => ({ data: undefined }),
+      promptAsync: async () => ({ data: undefined }),
       command: async () => ({ data: undefined }),
       abort: async () => ({ data: undefined }),
     },
@@ -40,7 +50,7 @@ beforeAll(async () => {
 
   mock.module("@solidjs/router", () => ({
     useNavigate: () => () => undefined,
-    useParams: () => ({}),
+    useParams: () => params,
   }))
 
   mock.module("@opencode-ai/sdk/v2/client", () => ({
@@ -62,7 +72,7 @@ beforeAll(async () => {
     useLocal: () => ({
       model: {
         current: () => ({ id: "model", provider: { id: "provider" } }),
-        variant: { current: () => undefined },
+        variant: { current: () => variant },
       },
       agent: {
         current: () => ({ name: "agent" }),
@@ -118,7 +128,11 @@ beforeAll(async () => {
       data: { command: [] },
       session: {
         optimistic: {
-          add: () => undefined,
+          add: (value: {
+            message: { agent: string; model: { providerID: string; modelID: string }; variant?: string }
+          }) => {
+            optimistic.push(value)
+          },
           remove: () => undefined,
         },
       },
@@ -155,9 +169,12 @@ beforeEach(() => {
   createdClients.length = 0
   createdSessions.length = 0
   enabledAutoAccept.length = 0
+  optimistic.length = 0
+  params = {}
   sentShell.length = 0
   syncedDirectories.length = 0
   selected = "/repo/worktree-a"
+  variant = undefined
 })
 
 describe("prompt submit worktree selection", () => {
@@ -219,4 +236,39 @@ describe("prompt submit worktree selection", () => {
 
     expect(enabledAutoAccept).toEqual([{ sessionID: "session-1", directory: "/repo/worktree-a" }])
   })
+
+  test("includes the selected variant on optimistic prompts", async () => {
+    params = { id: "session-1" }
+    variant = "high"
+
+    const submit = createPromptSubmit({
+      info: () => ({ id: "session-1" }),
+      imageAttachments: () => [],
+      commentCount: () => 0,
+      autoAccept: () => false,
+      mode: () => "normal",
+      working: () => false,
+      editor: () => undefined,
+      queueScroll: () => undefined,
+      promptLength: (value) => value.reduce((sum, part) => sum + ("content" in part ? part.content.length : 0), 0),
+      addToHistory: () => undefined,
+      resetHistoryNavigation: () => undefined,
+      setMode: () => undefined,
+      setPopover: () => undefined,
+      onSubmit: () => undefined,
+    })
+
+    const event = { preventDefault: () => undefined } as unknown as Event
+
+    await submit.handleSubmit(event)
+
+    expect(optimistic).toHaveLength(1)
+    expect(optimistic[0]).toMatchObject({
+      message: {
+        agent: "agent",
+        model: { providerID: "provider", modelID: "model" },
+        variant: "high",
+      },
+    })
+  })
 })
diff --git a/packages/app/src/components/prompt-input/submit.ts b/packages/app/src/components/prompt-input/submit.ts
index db1b5a5ca..fee6b070d 100644
--- a/packages/app/src/components/prompt-input/submit.ts
+++ b/packages/app/src/components/prompt-input/submit.ts
@@ -316,6 +316,7 @@ export function createPromptSubmit(input: PromptSubmitInput) {
       time: { created: Date.now() },
       agent,
       model,
+      variant,
     }
 
     const addOptimisticMessage = () =>
diff --git a/packages/app/src/context/sync.tsx b/packages/app/src/context/sync.tsx
index ed54751c3..562a2d19c 100644
--- a/packages/app/src/context/sync.tsx
+++ b/packages/app/src/context/sync.tsx
@@ -199,6 +199,7 @@ export const { use: useSync, provider: SyncProvider } = createSimpleContext({
           parts: Part[]
           agent: string
           model: { providerID: string; modelID: string }
+          variant?: string
         }) {
           const message: Message = {
             id: input.messageID,
@@ -207,6 +208,7 @@ export const { use: useSync, provider: SyncProvider } = createSimpleContext({
             time: { created: Date.now() },
             agent: input.agent,
             model: input.model,
+            variant: input.variant,
           }
           const [, setStore] = target()
           setOptimisticAdd(setStore as (...args: unknown[]) => void, {
diff --git a/packages/app/src/pages/session.tsx b/packages/app/src/pages/session.tsx
index cba49f5fb..ba9b14c12 100644
--- a/packages/app/src/pages/session.tsx
+++ b/packages/app/src/pages/session.tsx
@@ -36,6 +36,7 @@ import { createSessionComposerState, SessionComposerRegion } from "@/pages/sessi
 import { createOpenReviewFile, createSizing } from "@/pages/session/helpers"
 import { MessageTimeline } from "@/pages/session/message-timeline"
 import { type DiffStyle, SessionReviewTab, type SessionReviewTabProps } from "@/pages/session/review-tab"
+import { syncSessionModel } from "@/pages/session/session-model-helpers"
 import { createScrollSpy } from "@/pages/session/scroll-spy"
 import { SessionMobileTabs } from "@/pages/session/session-mobile-tabs"
 import { SessionSidePanel } from "@/pages/session/session-side-panel"
@@ -418,11 +419,7 @@ export default function Page() {
       () => {
         const msg = lastUserMessage()
         if (!msg) return
-        if (msg.agent) {
-          local.agent.set(msg.agent)
-          if (local.agent.current()?.model) return
-        }
-        if (msg.model) local.model.set(msg.model)
+        syncSessionModel(local, msg)
       },
     ),
   )
diff --git a/packages/app/src/pages/session/session-model-helpers.test.ts b/packages/app/src/pages/session/session-model-helpers.test.ts
new file mode 100644
index 000000000..ae8700ccd
--- /dev/null
+++ b/packages/app/src/pages/session/session-model-helpers.test.ts
@@ -0,0 +1,83 @@
+import { describe, expect, test } from "bun:test"
+import type { UserMessage } from "@opencode-ai/sdk/v2"
+import { syncSessionModel } from "./session-model-helpers"
+
+const message = (input?: Partial<Pick<UserMessage, "agent" | "model" | "variant">>) =>
+  ({
+    id: "msg",
+    sessionID: "session",
+    role: "user",
+    time: { created: 1 },
+    agent: input?.agent ?? "build",
+    model: input?.model ?? { providerID: "anthropic", modelID: "claude-sonnet-4" },
+    variant: input?.variant,
+  }) as UserMessage
+
+describe("syncSessionModel", () => {
+  test("restores the last message model and variant", () => {
+    const calls: unknown[] = []
+
+    syncSessionModel(
+      {
+        agent: {
+          set(value) {
+            calls.push(["agent", value])
+          },
+        },
+        model: {
+          set(value) {
+            calls.push(["model", value])
+          },
+          current() {
+            return { id: "claude-sonnet-4", provider: { id: "anthropic" } }
+          },
+          variant: {
+            set(value) {
+              calls.push(["variant", value])
+            },
+          },
+        },
+      },
+      message({ variant: "high" }),
+    )
+
+    expect(calls).toEqual([
+      ["agent", "build"],
+      ["model", { providerID: "anthropic", modelID: "claude-sonnet-4" }],
+      ["variant", "high"],
+    ])
+  })
+
+  test("skips variant when the model falls back", () => {
+    const calls: unknown[] = []
+
+    syncSessionModel(
+      {
+        agent: {
+          set(value) {
+            calls.push(["agent", value])
+          },
+        },
+        model: {
+          set(value) {
+            calls.push(["model", value])
+          },
+          current() {
+            return { id: "gpt-5", provider: { id: "openai" } }
+          },
+          variant: {
+            set(value) {
+              calls.push(["variant", value])
+            },
+          },
+        },
+      },
+      message({ variant: "high" }),
+    )
+
+    expect(calls).toEqual([
+      ["agent", "build"],
+      ["model", { providerID: "anthropic", modelID: "claude-sonnet-4" }],
+    ])
+  })
+})
diff --git a/packages/app/src/pages/session/session-model-helpers.ts b/packages/app/src/pages/session/session-model-helpers.ts
new file mode 100644
index 000000000..ab181df59
--- /dev/null
+++ b/packages/app/src/pages/session/session-model-helpers.ts
@@ -0,0 +1,33 @@
+import type { UserMessage } from "@opencode-ai/sdk/v2"
+import { batch } from "solid-js"
+
+type Local = {
+  agent: {
+    set(name: string | undefined): void
+  }
+  model: {
+    set(model: UserMessage["model"] | undefined): void
+    current():
+      | {
+          id: string
+          provider: { id: string }
+        }
+      | undefined
+    variant: {
+      set(value: string | undefined): void
+    }
+  }
+}
+
+export const syncSessionModel = (local: Local, msg: UserMessage) => {
+  batch(() => {
+    local.agent.set(msg.agent)
+    local.model.set(msg.model)
+  })
+
+  const model = local.model.current()
+  if (!model) return
+  if (model.provider.id !== msg.model.providerID) return
+  if (model.id !== msg.model.modelID) return
+  local.model.variant.set(msg.variant)
+}