feat: support claude agent SDK-style structured outputs in the OpenCode SDK (#8161)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
Co-authored-by: Dax Raad <d@ironbay.co>

packages/opencode/src/session/message-v2.ts

@@ -15,6 +15,13 @@ import type { Provider } from "@/provider/provider"
 export namespace MessageV2 {
   export const OutputLengthError = NamedError.create("MessageOutputLengthError", z.object({}))
   export const AbortedError = NamedError.create("MessageAbortedError", z.object({ message: z.string() }))
+  export const StructuredOutputError = NamedError.create(
+    "StructuredOutputError",
+    z.object({
+      message: z.string(),
+      retries: z.number(),
+    }),
+  )
   export const AuthError = NamedError.create(
     "ProviderAuthError",
     z.object({
@@ -39,6 +46,29 @@ export namespace MessageV2 {
     z.object({ message: z.string(), responseBody: z.string().optional() }),
   )
 
+  export const OutputFormatText = z
+    .object({
+      type: z.literal("text"),
+    })
+    .meta({
+      ref: "OutputFormatText",
+    })
+
+  export const OutputFormatJsonSchema = z
+    .object({
+      type: z.literal("json_schema"),
+      schema: z.record(z.string(), z.any()).meta({ ref: "JSONSchema" }),
+      retryCount: z.number().int().min(0).default(2),
+    })
+    .meta({
+      ref: "OutputFormatJsonSchema",
+    })
+
+  export const Format = z.discriminatedUnion("type", [OutputFormatText, OutputFormatJsonSchema]).meta({
+    ref: "OutputFormat",
+  })
+  export type OutputFormat = z.infer<typeof Format>
+
   const PartBase = z.object({
     id: z.string(),
     sessionID: z.string(),
@@ -313,6 +343,7 @@ export namespace MessageV2 {
     time: z.object({
       created: z.number(),
     }),
+    format: Format.optional(),
     summary: z
       .object({
         title: z.string().optional(),
@@ -365,6 +396,7 @@ export namespace MessageV2 {
         NamedError.Unknown.Schema,
         OutputLengthError.Schema,
         AbortedError.Schema,
+        StructuredOutputError.Schema,
         ContextOverflowError.Schema,
         APIError.Schema,
       ])
@@ -393,6 +425,7 @@ export namespace MessageV2 {
         write: z.number(),
       }),
     }),
+    structured: z.any().optional(),
     variant: z.string().optional(),
     finish: z.string().optional(),
   }).meta({