feat(core): widen interleaved reasoning fields

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

@@ -289,6 +289,24 @@ describe("Config", () => {
     }),
   )
 
+  it.effect("migrates provider-specific interleaved reasoning fields", () =>
+    Effect.sync(() => {
+      const migrated = ConfigMigrateV1.migrate({
+        provider: {
+          custom: {
+            models: {
+              chat: { interleaved: { field: "vendor_reasoning" } },
+            },
+          },
+        },
+      })
+
+      expect(migrated.providers?.custom?.models?.chat?.capabilities?.interleaved).toEqual({
+        field: "vendor_reasoning",
+      })
+    }),
+  )
+
   it.effect("migrates v1 provider lists to policies", () =>
     Effect.sync(() => {
       expect(

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

@@ -170,7 +170,12 @@ describe("ConfigProviderPlugin.Plugin", () => {
                       models: {
                         chat: {
                           name: "First",
-                          capabilities: { tools: true, input: ["text"], output: ["text"] },
+                          capabilities: {
+                            tools: true,
+                            input: ["text"],
+                            output: ["text"],
+                            interleaved: { field: "vendor_reasoning" },
+                          },
                           disabled: true,
                           limit: { context: 100, output: 50 },
                           cost: { input: 1, output: 2 },
@@ -251,7 +256,12 @@ describe("ConfigProviderPlugin.Plugin", () => {
         expect(model.id).toBe(modelID)
         expect(model.modelID).toBe(ModelV2.ID.make("api-chat"))
         expect(model.name).toBe("Last")
-        expect(model.capabilities).toEqual({ tools: true, input: ["text"], output: ["text"] })
+        expect(model.capabilities).toEqual({
+          tools: true,
+          input: ["text"],
+          output: ["text"],
+          interleaved: { field: "vendor_reasoning" },
+        })
         expect(model.enabled).toBe(false)
         expect(model.limit).toEqual({ context: 100, output: 75 })
         expect(model.cost).toEqual([

packages/core/test/models.test.ts

@@ -47,6 +47,7 @@ const fixture = {
         reasoning: false,
         temperature: true,
         tool_call: true,
+        interleaved: { field: "vendor_reasoning" },
         limit: { context: 128000, output: 8192 },
       },
     },
@@ -69,7 +70,7 @@ const fixtureSnapshot = [
         family: undefined,
         package: undefined,
         settings: undefined,
-        capabilities: { tools: true, input: [], output: [] },
+        capabilities: { tools: true, input: [], output: [], interleaved: { field: "vendor_reasoning" } },
         variants: [],
         time: { released: Date.parse("2026-01-01") },
         cost: [