diff --git a/.changeset/a2a-zod-schema-kind.md b/.changeset/a2a-zod-schema-kind.md
new file mode 100644
index 00000000..27b822b6
--- /dev/null
+++ b/.changeset/a2a-zod-schema-kind.md
@@ -0,0 +1,19 @@
+---
+"@agentcommercekit/ack-id": minor
+---
+
+The Zod A2A schemas now describe the same messages as their Valibot twins.
+
+`@agentcommercekit/ack-id/a2a/schemas/zod` still described the pre-0.3 A2A
+shape: parts were discriminated on `type` rather than `kind`, and `messageSchema`
+required neither `kind: "message"` nor `messageId`. The Valibot schemas moved to
+the `@a2a-js/sdk` shape and the Zod ones were left behind, so the two entry
+points disagreed about the same message. A handshake message produced by
+`createA2AHandshakeMessage` failed Zod validation, while a message shaped for
+the Zod schemas was rejected at verification time by `verifyA2AHandshakeMessage`.
+
+`messageSchema` now requires `kind: "message"` and `messageId` and accepts
+`taskId`, `contextId`, `extensions`, and `referenceTaskIds`. `partSchema`
+discriminates on `kind`. `fileContentSchema` is replaced by `fileWithBytesSchema`
+and `fileWithUriSchema`, matching the Valibot exports, and a file part accepts
+either.
diff --git a/packages/ack-id/src/a2a/schemas/schemas.test.ts b/packages/ack-id/src/a2a/schemas/schemas.test.ts
new file mode 100644
index 00000000..d6b5decd
--- /dev/null
+++ b/packages/ack-id/src/a2a/schemas/schemas.test.ts
@@ -0,0 +1,99 @@
+import * as v from "valibot"
+import { describe, expect, it } from "vitest"
+
+import { createA2AHandshakeMessageFromJwt } from "../sign-message"
+import { messageSchema as valibotMessageSchema } from "./valibot"
+import { messageSchema as zodMessageSchema } from "./zod"
+
+// The two schema files are separate entry points onto the same A2A shape, so
+// every case runs against both. A message that one accepts and the other
+// rejects is exactly the drift these tests exist to catch.
+const validators = {
+  valibot: (value: unknown) => v.safeParse(valibotMessageSchema, value).success,
+  zod: (value: unknown) => zodMessageSchema.safeParse(value).success,
+}
+
+describe.each(Object.entries(validators))(
+  "A2A messageSchema (%s)",
+  (_name, accepts) => {
+    it("accepts a handshake message built by this package", () => {
+      expect(accepts(createA2AHandshakeMessageFromJwt("user", "a.b.c"))).toBe(
+        true,
+      )
+    })
+
+    it("accepts a text message carrying task and context ids", () => {
+      expect(
+        accepts({
+          kind: "message",
+          messageId: "msg-1",
+          role: "agent",
+          parts: [{ kind: "text", text: "hello" }],
+          taskId: "task-1",
+          contextId: "ctx-1",
+        }),
+      ).toBe(true)
+    })
+
+    it("accepts a file part carrying a uri", () => {
+      expect(
+        accepts({
+          kind: "message",
+          messageId: "msg-1",
+          role: "user",
+          parts: [
+            { kind: "file", file: { uri: "https://example.com/receipt.pdf" } },
+          ],
+        }),
+      ).toBe(true)
+    })
+
+    it("accepts a file part carrying bytes", () => {
+      expect(
+        accepts({
+          kind: "message",
+          messageId: "msg-1",
+          role: "user",
+          parts: [
+            {
+              kind: "file",
+              file: { mimeType: "application/pdf", bytes: "aGVsbG8=" },
+            },
+          ],
+        }),
+      ).toBe(true)
+    })
+
+    // `@a2a-js/sdk` v0.3 keys parts on `kind`. `type` is the pre-0.3 spelling.
+    it("rejects a part keyed on type instead of kind", () => {
+      expect(
+        accepts({
+          kind: "message",
+          messageId: "msg-1",
+          role: "user",
+          parts: [{ type: "text", text: "hello" }],
+        }),
+      ).toBe(false)
+    })
+
+    it("rejects a message without a message kind", () => {
+      expect(
+        accepts({
+          messageId: "msg-1",
+          role: "user",
+          parts: [{ kind: "text", text: "hello" }],
+        }),
+      ).toBe(false)
+    })
+
+    it("rejects a message without a messageId", () => {
+      expect(
+        accepts({
+          kind: "message",
+          role: "user",
+          parts: [{ kind: "text", text: "hello" }],
+        }),
+      ).toBe(false)
+    })
+  },
+)
diff --git a/packages/ack-id/src/a2a/schemas/zod.ts b/packages/ack-id/src/a2a/schemas/zod.ts
index f6575bd0..99ff175d 100644
--- a/packages/ack-id/src/a2a/schemas/zod.ts
+++ b/packages/ack-id/src/a2a/schemas/zod.ts
@@ -11,32 +11,38 @@ const partBaseSchema = z.object({
 
 // Text part schema
 export const textPartSchema = partBaseSchema.extend({
-  type: z.literal("text"),
+  kind: z.literal("text"),
   text: z.string(),
 })
 
 // Data part schema
 export const dataPartSchema = partBaseSchema.extend({
-  type: z.literal("data"),
+  kind: z.literal("data"),
   data: z.union([z.record(z.string(), z.unknown()), z.array(z.unknown())]),
 })
 
-// File content schema
-export const fileContentSchema = z.object({
+// File content schemas
+export const fileWithBytesSchema = z.object({
   name: z.string().nullable().optional(),
   mimeType: z.string().nullable().optional(),
   bytes: z.string().nullable().optional(),
   uri: z.string().nullable().optional(),
 })
 
+export const fileWithUriSchema = z.object({
+  name: z.string().nullable().optional(),
+  mimeType: z.string().nullable().optional(),
+  uri: z.string().nullable().optional(),
+})
+
 // File part schema
 export const filePartSchema = partBaseSchema.extend({
-  type: z.literal("file"),
-  file: fileContentSchema,
+  kind: z.literal("file"),
+  file: z.union([fileWithBytesSchema, fileWithUriSchema]),
 })
 
 // Union of all part types using discriminated union
-export const partSchema = z.discriminatedUnion("type", [
+export const partSchema = z.discriminatedUnion("kind", [
   textPartSchema,
   dataPartSchema,
   filePartSchema,
@@ -44,7 +50,13 @@ export const partSchema = z.discriminatedUnion("type", [
 
 // Message schema
 export const messageSchema = z.looseObject({
+  kind: z.literal("message"),
+  messageId: z.string(),
   role: roleSchema,
   parts: z.array(partSchema),
   metadata: metadataSchema.optional(),
+  taskId: z.string().optional(),
+  contextId: z.string().optional(),
+  extensions: z.array(z.string()).optional(),
+  referenceTaskIds: z.array(z.string()).optional(),
 })