feat(ai): support custom reasoning fields (#38227)

packages/core/test/config/config.test.ts

@@ -419,6 +419,28 @@ describe("Config", () => {
     }),
   )
 
+  it.effect("migrates v1 interleaved fields to compatibility", () =>
+    Effect.sync(() => {
+      const migrated = ConfigMigrateV1.migrate({
+        provider: {
+          custom: {
+            models: {
+              object: { interleaved: { field: "vendor_reasoning" } },
+              string: { interleaved: "reasoning_text" },
+              boolean: { interleaved: true },
+            },
+          },
+        },
+      })
+
+      expect(migrated.providers?.custom?.models?.object?.compatibility).toEqual({
+        reasoningField: "vendor_reasoning",
+      })
+      expect(migrated.providers?.custom?.models?.string?.compatibility).toEqual({ reasoningField: "reasoning_text" })
+      expect(migrated.providers?.custom?.models?.boolean?.compatibility).toBeUndefined()
+    }),
+  )
+
   it.effect("migrates v1 command configuration", () =>
     Effect.sync(() => {
       expect(

packages/core/test/config/provider.test.ts

@@ -170,6 +170,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
                       models: {
                         chat: {
                           name: "First",
+                          compatibility: { reasoningField: "vendor_reasoning" },
                           capabilities: { tools: true, input: ["text"], output: ["text"] },
                           disabled: true,
                           limit: { context: 100, output: 50 },
@@ -251,6 +252,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
         expect(model.id).toBe(modelID)
         expect(model.modelID).toBe(ModelV2.ID.make("api-chat"))
         expect(model.name).toBe("Last")
+        expect(model.compatibility).toEqual({ reasoningField: "vendor_reasoning" })
         expect(model.capabilities).toEqual({ tools: true, input: ["text"], output: ["text"] })
         expect(model.enabled).toBe(false)
         expect(model.limit).toEqual({ context: 100, output: 75 })

packages/core/test/models.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, beforeEach, afterAll } from "bun:test"
+import { describe, expect, beforeEach, afterAll, test } from "bun:test"
 import { Money } from "@opencode-ai/schema/money"
 import { Effect, Layer, Ref } from "effect"
 import { HttpClient, HttpClientResponse } from "effect/unstable/http"
@@ -15,6 +15,13 @@ import path from "path"
 
 const cacheFile = path.join(Global.Path.cache, "models.json")
 
+test("normalizes permissive interleaved values to compatibility", () => {
+  expect(ModelV2.compatibility("reasoning_text")).toEqual({ reasoningField: "reasoning_text" })
+  expect(ModelV2.compatibility({ field: "vendor_reasoning" })).toEqual({ reasoningField: "vendor_reasoning" })
+  expect(ModelV2.compatibility(true)).toBeUndefined()
+  expect(ModelV2.compatibility(false)).toBeUndefined()
+})
+
 const fixture = {
   acme: {
     id: "acme",
@@ -30,6 +37,7 @@ const fixture = {
         reasoning: false,
         temperature: true,
         tool_call: true,
+        interleaved: { field: "vendor_reasoning" },
         limit: { context: 128000, output: 8192 },
       },
     },
@@ -49,6 +57,7 @@ const fixtureSnapshot = [
         modelID: ModelV2.ID.make("acme-1"),
         providerID: ProviderV2.ID.make("acme"),
         name: "Acme One",
+        compatibility: { reasoningField: "vendor_reasoning" },
         family: undefined,
         package: undefined,
         settings: undefined,

packages/core/test/session-runner-model.test.ts

@@ -16,6 +16,7 @@ import { it } from "./lib/effect"
 
 interface ModelOptions {
   readonly modelID?: string
+  readonly compatibility?: ModelV2.Compatibility
   readonly settings?: ModelV2.Info["settings"]
   readonly headers?: ModelV2.Info["headers"]
   readonly body?: ModelV2.Info["body"]
@@ -28,6 +29,7 @@ const model = (packageName: string | undefined, options: ModelOptions = {}) =>
     modelID: ModelV2.ID.make(options.modelID ?? "api-test-model"),
     providerID: ProviderV2.ID.make("test-provider"),
     name: "Test model",
+    compatibility: options.compatibility,
     package: packageName,
     settings: options.settings ?? {},
     headers: options.headers ?? { "x-test": "header" },
@@ -101,6 +103,7 @@ describe("SessionRunnerModel", () => {
     Effect.gen(function* () {
       const resolved = yield* SessionRunnerModel.fromCatalogModel(
         model(ProviderV2.aisdk("@ai-sdk/openai-compatible"), {
+          compatibility: { reasoningField: "vendor_reasoning" },
           settings: {
             apiKey: "settings-secret",
             baseURL: "https://compatible.example/v1",
@@ -121,6 +124,7 @@ describe("SessionRunnerModel", () => {
 
       expect(headers.authorization).toBe("Bearer settings-secret")
       expect(resolved.route.id).toBe("openai-compatible-chat")
+      expect(resolved.compatibility?.reasoningField).toBe("vendor_reasoning")
       expect(resolved.route.endpoint.baseURL).toBe("https://compatible.example/v1")
       expect(resolved.route.defaults.http?.body).toEqual({})
     }),