feat(app): extract prompt state and add composer model selection (#36227)

packages/app/src/pages/session/session-model-helpers.ts

@@ -7,6 +7,24 @@ type Local = {
   }
 }
 
+type ModelSelection = {
+  model: {
+    current(): { id: string; provider: { id: string } } | undefined
+    set(model: { providerID: string; modelID: string }): void
+    variant: {
+      current(): string | undefined
+      set(variant: string | undefined): void
+    }
+  }
+}
+
+type PromptState = {
+  model: {
+    current(): { providerID: string; modelID: string; variant?: string | null } | undefined
+    set(model: { providerID: string; modelID: string; variant?: string | null }): void
+  }
+}
+
 export const resetSessionModel = (local: Local) => {
   local.session.reset()
 }
@@ -14,3 +32,32 @@ export const resetSessionModel = (local: Local) => {
 export const syncSessionModel = (local: Local, msg: UserMessage) => {
   local.session.restore(msg)
 }
+
+export const syncPromptModel = (local: ModelSelection, prompt: PromptState) => {
+  const model = local.model.current()
+  if (!model) return
+  const next = {
+    providerID: model.provider.id,
+    modelID: model.id,
+    variant: local.model.variant.current(),
+  }
+  const current = prompt.model.current()
+  if (current?.providerID === next.providerID && current.modelID === next.modelID && current.variant === next.variant)
+    return
+  prompt.model.set(next)
+}
+
+export const restorePromptModel = (local: ModelSelection, prompt: PromptState) => {
+  const model = prompt.model.current()
+  if (!model) return false
+  const current = local.model.current()
+  if (
+    current?.provider.id === model.providerID &&
+    current.id === model.modelID &&
+    local.model.variant.current() === (model.variant ?? undefined)
+  )
+    return true
+  local.model.set({ providerID: model.providerID, modelID: model.modelID })
+  local.model.variant.set(model.variant ?? undefined)
+  return true
+}