fix(opencode): honor agent tool_choice config

packages/core/src/v1/config/agent.ts

@@ -17,6 +17,9 @@ const AgentSchema = Schema.StructWithRest(
     }),
     temperature: Schema.optional(Schema.Finite),
     top_p: Schema.optional(Schema.Finite),
+    tool_choice: Schema.optional(Schema.Literals(["auto", "required", "none"])).annotate({
+      description: "How the model selects tools for this agent (default: auto).",
+    }),
     prompt: Schema.optional(Schema.String),
     tools: Schema.optional(Schema.Record(Schema.String, Schema.Boolean)).annotate({
       description: "@deprecated Use 'permission' field instead",
@@ -48,6 +51,7 @@ const KNOWN_KEYS = new Set([
   "description",
   "temperature",
   "top_p",
+  "tool_choice",
   "mode",
   "hidden",
   "color",

packages/core/test/config/agent-v1.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, test } from "bun:test"
+import { Schema } from "effect"
+import { ConfigAgentV1 } from "@opencode-ai/core/v1/config/agent"
+
+const decode = Schema.decodeUnknownSync(ConfigAgentV1.Info)
+
+describe("ConfigAgentV1 tool_choice", () => {
+  test("keeps tool_choice as a known top-level field", () => {
+    const agent = decode({ tool_choice: "required" })
+    expect(agent.tool_choice).toBe("required")
+    expect(agent.options?.["tool_choice"]).toBeUndefined()
+  })
+
+  test("rejects an unknown tool_choice value", () => {
+    expect(() => decode({ tool_choice: "sometimes" })).toThrow()
+  })
+})

packages/opencode/src/agent/agent.ts

@@ -40,6 +40,7 @@ export const Info = Schema.Struct({
   hidden: Schema.optional(Schema.Boolean),
   topP: Schema.optional(Schema.Finite),
   temperature: Schema.optional(Schema.Finite),
+  toolChoice: Schema.optional(Schema.Literals(["auto", "required", "none"])),
   color: Schema.optional(Schema.String),
   permission: PermissionV1.Ruleset,
   model: Schema.optional(
@@ -282,6 +283,7 @@ export const layer = Layer.effect(
           item.description = value.description ?? item.description
           item.temperature = value.temperature ?? item.temperature
           item.topP = value.top_p ?? item.topP
+          item.toolChoice = value.tool_choice ?? item.toolChoice
           item.mode = value.mode ?? item.mode
           item.color = value.color ?? item.color
           item.hidden = value.hidden ?? item.hidden

packages/opencode/src/session/prompt.ts

@@ -1343,7 +1343,7 @@ export const layer = Layer.effect(
               messages: [...modelMsgs, ...(isLastStep ? [{ role: "assistant" as const, content: MAX_STEPS }] : [])],
               tools,
               model,
-              toolChoice: format.type === "json_schema" ? "required" : undefined,
+              toolChoice: format.type === "json_schema" ? "required" : agent.toolChoice,
             })
 
             if (structured !== undefined) {