refactor(llm): share tool choice lowering

packages/llm/src/protocols/anthropic-messages.ts

@@ -209,15 +209,13 @@ const lowerTool = (tool: ToolDefinition): AnthropicTool => ({
   input_schema: tool.inputSchema,
 })
 
-const lowerToolChoice = Effect.fn("AnthropicMessages.lowerToolChoice")(function* (
-  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
-) {
-  if (toolChoice.type === "none") return undefined
-  if (toolChoice.type === "required") return { type: "any" as const }
-  if (toolChoice.type !== "tool") return { type: "auto" as const }
-  if (!toolChoice.name) return yield* invalid("Anthropic Messages tool choice requires a tool name")
-  return { type: "tool" as const, name: toolChoice.name }
-})
+const lowerToolChoice = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
+  ProviderShared.matchToolChoice("Anthropic Messages", toolChoice, {
+    auto: () => ({ type: "auto" as const }),
+    none: () => undefined,
+    required: () => ({ type: "any" as const }),
+    tool: (name) => ({ type: "tool" as const, name }),
+  })
 
 const lowerToolCall = (part: ToolCallPart): AnthropicToolUseBlock => ({
   type: "tool_use",

packages/llm/src/protocols/bedrock-converse.ts

@@ -232,15 +232,13 @@ const textWithCache = (text: string, cache: CacheHint | undefined): Array<Bedroc
   return cachePoint ? [{ text }, cachePoint] : [{ text }]
 }
 
-const lowerToolChoice = Effect.fn("BedrockConverse.lowerToolChoice")(function* (
-  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
-) {
-  if (toolChoice.type === "none") return undefined
-  if (toolChoice.type === "required") return { any: {} } as const
-  if (toolChoice.type !== "tool") return { auto: {} } as const
-  if (!toolChoice.name) return yield* invalid("Bedrock Converse tool choice requires a tool name")
-  return { tool: { name: toolChoice.name } } as const
-})
+const lowerToolChoice = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
+  ProviderShared.matchToolChoice("Bedrock Converse", toolChoice, {
+    auto: () => ({ auto: {} }) as const,
+    none: () => undefined,
+    required: () => ({ any: {} }) as const,
+    tool: (name) => ({ tool: { name } }) as const,
+  })
 
 const lowerToolCall = (part: ToolCallPart): BedrockToolUseBlock => ({
   toolUse: {

packages/llm/src/protocols/gemini.ts

@@ -170,17 +170,13 @@ const lowerTool = (tool: ToolDefinition) => ({
   parameters: GeminiToolSchema.convert(tool.inputSchema),
 })
 
-const lowerToolConfig = Effect.fn("Gemini.lowerToolConfig")(function* (
-  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
-) {
-  if (toolChoice.type === "required") return { functionCallingConfig: { mode: "ANY" as const } }
-  if (toolChoice.type === "none") return { functionCallingConfig: { mode: "NONE" as const } }
-  if (toolChoice.type !== "tool") return { functionCallingConfig: { mode: "AUTO" as const } }
-  if (!toolChoice.name) return yield* invalid("Gemini tool choice requires a tool name")
-  return {
-    functionCallingConfig: { mode: "ANY" as const, allowedFunctionNames: [toolChoice.name] },
-  }
-})
+const lowerToolConfig = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
+  ProviderShared.matchToolChoice("Gemini", toolChoice, {
+    auto: () => ({ functionCallingConfig: { mode: "AUTO" as const } }),
+    none: () => ({ functionCallingConfig: { mode: "NONE" as const } }),
+    required: () => ({ functionCallingConfig: { mode: "ANY" as const } }),
+    tool: (name) => ({ functionCallingConfig: { mode: "ANY" as const, allowedFunctionNames: [name] } }),
+  })
 
 const lowerUserPart = (part: TextPart | MediaPart) =>
   part.type === "text"

packages/llm/src/protocols/openai-chat.ts

@@ -166,13 +166,13 @@ const lowerTool = (tool: ToolDefinition): OpenAIChatTool => ({
   },
 })
 
-const lowerToolChoice = Effect.fn("OpenAIChat.lowerToolChoice")(function* (
-  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
-) {
-  if (toolChoice.type !== "tool") return toolChoice.type
-  if (!toolChoice.name) return yield* invalid("OpenAI Chat tool choice requires a tool name")
-  return { type: "function" as const, function: { name: toolChoice.name } }
-})
+const lowerToolChoice = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
+  ProviderShared.matchToolChoice("OpenAI Chat", toolChoice, {
+    auto: () => "auto" as const,
+    none: () => "none" as const,
+    required: () => "required" as const,
+    tool: (name) => ({ type: "function" as const, function: { name } }),
+  })
 
 const lowerToolCall = (part: ToolCallPart): OpenAIChatAssistantToolCall => ({
   id: part.id,

packages/llm/src/protocols/openai-responses.ts

@@ -158,13 +158,13 @@ const lowerTool = (tool: ToolDefinition): OpenAIResponsesTool => ({
   parameters: tool.inputSchema,
 })
 
-const lowerToolChoice = Effect.fn("OpenAIResponses.lowerToolChoice")(function* (
-  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
-) {
-  if (toolChoice.type !== "tool") return toolChoice.type
-  if (!toolChoice.name) return yield* invalid("OpenAI Responses tool choice requires a tool name")
-  return { type: "function" as const, name: toolChoice.name }
-})
+const lowerToolChoice = (toolChoice: NonNullable<LLMRequest["toolChoice"]>) =>
+  ProviderShared.matchToolChoice("OpenAI Responses", toolChoice, {
+    auto: () => "auto" as const,
+    none: () => "none" as const,
+    required: () => "required" as const,
+    tool: (name) => ({ type: "function" as const, name }),
+  })
 
 const lowerToolCall = (part: ToolCallPart): OpenAIResponsesInputItem => ({
   type: "function_call",

packages/llm/src/protocols/shared.ts

@@ -2,7 +2,7 @@ import { Buffer } from "node:buffer"
 import { Cause, Effect, Schema, Stream } from "effect"
 import * as Sse from "effect/unstable/encoding/Sse"
 import { Headers, HttpClientRequest, type HttpClientResponse } from "effect/unstable/http"
-import { InvalidRequestError, ProviderChunkError, type MediaPart, type ToolResultPart } from "../schema"
+import { InvalidRequestError, ProviderChunkError, type LLMRequest, type MediaPart, type ToolResultPart } from "../schema"
 
 export const Json = Schema.fromJsonString(Schema.Unknown)
 export const decodeJson = Schema.decodeUnknownSync(Json)
@@ -168,6 +168,24 @@ export const sseFraming = (
  */
 export const invalidRequest = (message: string) => new InvalidRequestError({ message })
 
+export const matchToolChoice = <Auto, None, Required, Tool>(
+  adapter: string,
+  toolChoice: NonNullable<LLMRequest["toolChoice"]>,
+  cases: {
+    readonly auto: () => Auto
+    readonly none: () => None
+    readonly required: () => Required
+    readonly tool: (name: string) => Tool
+  },
+) =>
+  Effect.gen(function* () {
+    if (toolChoice.type === "auto") return cases.auto()
+    if (toolChoice.type === "none") return cases.none()
+    if (toolChoice.type === "required") return cases.required()
+    if (!toolChoice.name) return yield* invalidRequest(`${adapter} tool choice requires a tool name`)
+    return cases.tool(toolChoice.name)
+  })
+
 /**
  * Build a `validate` step from a Schema decoder. Replaces the per-adapter
  * lambda body `(payload) => decode(payload).pipe(Effect.mapError((e) =>