From 0b8040a3be7bdb930588e3c8af2c9fa2c5cccb10 Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Wed, 6 May 2026 13:30:56 -0400
Subject: [PATCH] refactor(llm): move system helpers onto schema

---
 packages/llm/src/llm.ts    | 11 +++--------
 packages/llm/src/schema.ts | 14 ++++++++++++--
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/packages/llm/src/llm.ts b/packages/llm/src/llm.ts
index bca1b0be74..60415b87a7 100644
--- a/packages/llm/src/llm.ts
+++ b/packages/llm/src/llm.ts
@@ -10,10 +10,10 @@ import {
   HttpOptions,
   LLMRequest,
   Message,
+  SystemPart,
   ToolChoice,
   ToolDefinition,
   type ContentPart,
-  type SystemPart,
   ToolCallPart,
   ToolResultPart,
 } from "./schema"
@@ -50,12 +50,7 @@ export const limits = modelLimits
 
 export const text = Message.text
 
-export const system = (value: string): SystemPart => ({ type: "text", text: value })
-
-const systemParts = (input?: string | SystemPart | ReadonlyArray<SystemPart>) => {
-  if (input === undefined) return []
-  return typeof input === "string" ? [system(input)] : Array.isArray(input) ? [...input] : [input]
-}
+export const system = SystemPart.make
 
 export const message = Message.make
 
@@ -97,7 +92,7 @@ export const request = (input: RequestInput) => {
   } = input
   return new LLMRequest({
     ...rest,
-    system: systemParts(requestSystem),
+    system: SystemPart.content(requestSystem),
     messages: [...(messages?.map(message) ?? []), ...(prompt === undefined ? [] : [user(prompt)])],
     tools: tools?.map(toolDefinition) ?? [],
     toolChoice: requestToolChoice ? toolChoice(requestToolChoice) : undefined,
diff --git a/packages/llm/src/schema.ts b/packages/llm/src/schema.ts
index ccb3e26e7f..29ad8f3e22 100644
--- a/packages/llm/src/schema.ts
+++ b/packages/llm/src/schema.ts
@@ -253,13 +253,23 @@ export class CacheHint extends Schema.Class<CacheHint>("LLM.CacheHint")({
   ttlSeconds: Schema.optional(Schema.Number),
 }) {}
 
-export const SystemPart = Schema.Struct({
+const systemPartSchema = Schema.Struct({
   type: Schema.Literal("text"),
   text: Schema.String,
   cache: Schema.optional(CacheHint),
   metadata: Schema.optional(Schema.Record(Schema.String, Schema.Unknown)),
 }).annotate({ identifier: "LLM.SystemPart" })
-export type SystemPart = Schema.Schema.Type<typeof SystemPart>
+export type SystemPart = Schema.Schema.Type<typeof systemPartSchema>
+
+const makeSystemPart = (text: string): SystemPart => ({ type: "text", text })
+
+export const SystemPart = Object.assign(systemPartSchema, {
+  make: makeSystemPart,
+  content: (input?: string | SystemPart | ReadonlyArray<SystemPart>) => {
+    if (input === undefined) return []
+    return typeof input === "string" ? [makeSystemPart(input)] : Array.isArray(input) ? [...input] : [input]
+  },
+})
 
 export const TextPart = Schema.Struct({
   type: Schema.Literal("text"),