agent_patch

diff --git a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/classic/schemas.ts b/app/packages/zod/src/v4/classic/schemas.ts
index 737446a..56132e1 100644
--- a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/classic/schemas.ts
+++ b/app/packages/zod/src/v4/classic/schemas.ts
@@ -88,6 +88,10 @@ export interface ZodType<
   ): Promise<parse.ZodSafeParseResult<core.output<this>>>;
 
   // refinements
+  refine<RefinedOutput extends core.output<this>>(
+    check: (arg: core.output<this>) => arg is RefinedOutput,
+    params?: string | core.$ZodCustomParams
+  ): this & core.$ZodType<RefinedOutput, core.input<this>>;
   refine(check: (arg: core.output<this>) => unknown | Promise<unknown>, params?: string | core.$ZodCustomParams): this;
   superRefine(
     refinement: (arg: core.output<this>, ctx: core.$RefinementCtx<core.output<this>>) => void | Promise<void>
@@ -199,7 +203,7 @@ export const ZodType: core.$constructor<ZodType> = /*@__PURE__*/ core.$construct
   inst.safeDecodeAsync = async (data, params) => parse.safeDecodeAsync(inst, data, params);
 
   // refinements
-  inst.refine = (check, params) => inst.check(refine(check, params));
+  inst.refine = ((check, params) => inst.check(refine(check, params))) as any;
   inst.superRefine = (refinement) => inst.check(superRefine(refinement));
   inst.overwrite = (fn) => inst.check(checks.overwrite(fn));
 
@@ -2275,11 +2279,15 @@ export function custom<O>(
   return core._custom(ZodCustom, fn ?? (() => true), _params) as any;
 }
 
+export function refine<T, RefinedOutput extends T>(
+  fn: (arg: NoInfer<T>) => arg is RefinedOutput,
+  _params?: string | core.$ZodCustomParams
+): core.$ZodCheck<RefinedOutput>;
 export function refine<T>(
   fn: (arg: NoInfer<T>) => util.MaybeAsync<unknown>,
   _params: string | core.$ZodCustomParams = {}
 ): core.$ZodCheck<T> {
-  return core._refine(ZodCustom, fn, _params);
+  return core._refine(ZodCustom, fn, _params) as any;
 }
 
 // superRefine
diff --git a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/classic/tests/refine.test.ts b/app/packages/zod/src/v4/classic/tests/refine.test.ts
index 6eaff2d..e516b50 100644
--- a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/classic/tests/refine.test.ts
+++ b/app/packages/zod/src/v4/classic/tests/refine.test.ts
@@ -1,4 +1,4 @@
-import { describe, expect, test } from "vitest";
+import { describe, expect, expectTypeOf, test } from "vitest";
 import * as z from "zod/v4";
 
 describe("basic refinement functionality", () => {
@@ -416,6 +416,24 @@ describe("chained refinements", () => {
   });
 });
 
+describe("type predicates", () => {
+  test("refine narrows output type when using a type predicate", () => {
+    const schema = z.string().refine((arg): arg is "a" => arg === "a");
+
+    expectTypeOf<z.input<typeof schema>>().toEqualTypeOf<string>();
+    expectTypeOf<z.output<typeof schema>>().toEqualTypeOf<"a">();
+
+    expect(schema.safeParse("a").success).toEqual(true);
+    expect(schema.safeParse("b").success).toEqual(false);
+  });
+
+  test("refine keeps output type when using a non-predicate check", () => {
+    const schema = z.string().refine((arg) => arg.length > 0);
+
+    expectTypeOf<z.output<typeof schema>>().toEqualTypeOf<string>();
+  });
+});
+
 // Commented tests can be uncommented once type-checking issues are resolved
 /*
 describe("type refinement", () => {
diff --git a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/mini/schemas.ts b/app/packages/zod/src/v4/mini/schemas.ts
index 51e4c2a..0b7b274 100644
--- a/tmp/agent-patch-flux-pr-5575.1-of-1.2026-02-27__21-30-28__gpt-5-3-codex/app/packages/zod/src/v4/mini/schemas.ts
+++ b/app/packages/zod/src/v4/mini/schemas.ts
@@ -1639,11 +1639,15 @@ export function custom<O = unknown, I = O>(
 }
 
 // refine
+export function refine<T, RefinedOutput extends T>(
+  fn: (arg: NoInfer<T>) => arg is RefinedOutput,
+  _params?: string | core.$ZodCustomParams
+): core.$ZodCheck<RefinedOutput>;
 export function refine<T>(
   fn: (arg: NoInfer<T>) => util.MaybeAsync<unknown>,
   _params: string | core.$ZodCustomParams = {}
 ): core.$ZodCheck<T> {
-  return core._refine(ZodMiniCustom, fn, _params);
+  return core._refine(ZodMiniCustom, fn, _params) as any;
 }
 
 // superRefine