diff --git a/agent/lib/google-workspace/gmail.ts b/agent/lib/google-workspace/gmail.ts
index e23ee6f2..154c256b 100644
--- a/agent/lib/google-workspace/gmail.ts
+++ b/agent/lib/google-workspace/gmail.ts
@@ -73,11 +73,23 @@ export async function readGmailThread(ctx: ToolContext, threadId: string) {
     );
     return {
       id: thread.id ?? threadId,
-      messages: (thread.messages ?? []).slice(-20).map((message) =>
-        Object.assign({}, minimizeMessage(message), {
-          attachments: collectAttachments(message.payload),
-          body: redactGoogleText(plainText(message.payload)),
-        })
+      messages: await Promise.all(
+        (thread.messages ?? []).slice(-20).map(async (message) =>
+          Object.assign({}, minimizeMessage(message), {
+            attachments: collectAttachments(message.payload),
+            body: redactGoogleText(
+              await plainText(message.payload, async (attachmentId) => {
+                if (!message.id)
+                  throw new Error("The Gmail message has no ID.");
+                const { data } = await client.users.messages.attachments.get(
+                  { id: attachmentId, messageId: message.id, userId: "me" },
+                  { signal: ctx.abortSignal }
+                );
+                return data.data ?? "";
+              })
+            ),
+          })
+        )
       ),
     };
   });
@@ -174,20 +186,29 @@ function header(part: GmailPart | undefined, name: string) {
   );
 }
 
-function plainText(part: GmailPart | undefined): string {
-  if (!part) return "";
-  if (part.mimeType === "text/plain" && part.body?.data) {
-    return decodeBase64Url(part.body.data);
+async function plainText(
+  part: GmailPart | undefined,
+  readAttachment: (attachmentId: string) => Promise<string>
+): Promise<string> {
+  if (!part || part.filename) return "";
+  if (part.mimeType === "text/plain" || part.mimeType === "text/html") {
+    let data = part.body?.data;
+    if (!data && part.body?.attachmentId) {
+      data = await readAttachment(part.body.attachmentId);
+    }
+    if (data) {
+      const text = decodeBase64Url(data);
+      return part.mimeType === "text/plain"
+        ? text
+        : text.replace(/<[^>]+>/gu, " ").replace(/\s+/gu, " ");
+    }
   }
+  /* oxlint-disable eslint/no-await-in-loop -- Preserve MIME body order and stop after the first readable body. */
   for (const child of part.parts ?? []) {
-    const text = plainText(child);
+    const text = await plainText(child, readAttachment);
     if (text) return text;
   }
-  if (part.mimeType === "text/html" && part.body?.data) {
-    return decodeBase64Url(part.body.data)
-      .replace(/<[^>]+>/gu, " ")
-      .replace(/\s+/gu, " ");
-  }
+  /* oxlint-enable eslint/no-await-in-loop */
   return "";
 }
 
diff --git a/agent/lib/google-workspace/tests/gmail-body.test.ts b/agent/lib/google-workspace/tests/gmail-body.test.ts
new file mode 100644
index 00000000..f8e207af
--- /dev/null
+++ b/agent/lib/google-workspace/tests/gmail-body.test.ts
@@ -0,0 +1,241 @@
+import { createServer } from "node:http";
+import * as GmailApi from "@googleapis/gmail";
+import type { ToolContext } from "eve/tools";
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi,
+} from "vitest";
+import { z } from "zod";
+import { gmailReadThread } from "@agent/tools/gmail";
+import { toolContextFor } from "@tests/helpers/tool-context";
+
+let thread: GmailApi.gmail_v1.Schema$Thread = {};
+const bodies = new Map<string, GmailApi.gmail_v1.Schema$MessagePartBody>();
+const requests: { authorization: string | undefined; path: string }[] = [];
+const server = createServer((request, response) => {
+  const url = new URL(request.url ?? "/", "http://localhost");
+  requests.push({
+    authorization: request.headers.authorization,
+    path: url.pathname,
+  });
+  response.setHeader("content-type", "application/json");
+  if (url.pathname === "/gmail/v1/users/me/threads/thread-fixture") {
+    response.end(JSON.stringify(thread));
+    return;
+  }
+  const body = bodies.get(url.pathname);
+  if (body) {
+    response.end(JSON.stringify(body));
+    return;
+  }
+  response.statusCode = 404;
+  response.end(JSON.stringify({ error: { message: "Unknown fixture path" } }));
+});
+
+beforeAll(async () => {
+  await new Promise<void>((resolve) => server.listen(0, "127.0.0.1", resolve));
+  const address = z.object({ port: z.number() }).parse(server.address());
+  const rootUrl = `http://127.0.0.1:${String(address.port)}`;
+  // Keep the generated Google client, OAuth header and transport; only redirect the external SDK boundary to the local fixture.
+  vi.spyOn(GmailApi, "gmail").mockImplementation(
+    (options) => new GmailApi.gmail_v1.Gmail({ ...options, rootUrl })
+  );
+});
+
+beforeEach(() => {
+  bodies.clear();
+  requests.length = 0;
+  thread = { id: "thread-fixture", messages: [] };
+});
+
+afterAll(async () => {
+  vi.restoreAllMocks();
+  await new Promise<void>((resolve, reject) =>
+    server.close((error) => {
+      if (error) reject(error);
+      else resolve();
+    })
+  );
+});
+
+describe("Gmail thread text bodies", () => {
+  it.each([undefined, ""])(
+    "reads an external text body with data=%s through the generated attachments API",
+    async (data) => {
+      thread.messages = [
+        {
+          id: "message-fixture",
+          payload: {
+            body: { attachmentId: "body-fixture", data, size: 45 },
+            mimeType: "text/plain",
+          },
+        },
+      ];
+      bodies.set(
+        "/gmail/v1/users/me/messages/message-fixture/attachments/body-fixture",
+        { data: encode("Meet at noon. Your verification code is 123456.") }
+      );
+
+      const result = await gmailReadThread.execute(
+        { threadId: "thread-fixture" },
+        context()
+      );
+      expect(result).toMatchObject({
+        thread: {
+          messages: [
+            {
+              body: "Meet at noon. Your verification code is [six-digit code redacted].",
+            },
+          ],
+        },
+      });
+      expect(requests.map((request) => request.path)).toEqual([
+        "/gmail/v1/users/me/threads/thread-fixture",
+        "/gmail/v1/users/me/messages/message-fixture/attachments/body-fixture",
+      ]);
+      expect(
+        requests.every(
+          (request) => request.authorization === "Bearer fixture-token"
+        )
+      ).toBe(true);
+    }
+  );
+
+  it("keeps inline and empty text bodies without additional requests", async () => {
+    thread.messages = [
+      {
+        id: "inline",
+        payload: {
+          mimeType: "text/plain",
+          body: { data: encode("Inline text") },
+        },
+      },
+      { id: "empty", payload: { mimeType: "text/plain", body: { size: 0 } } },
+    ];
+    const result = await gmailReadThread.execute(
+      { threadId: "thread-fixture" },
+      context()
+    );
+    expect(result).toMatchObject({
+      thread: { messages: [{ body: "Inline text" }, { body: "" }] },
+    });
+    expect(requests).toHaveLength(1);
+  });
+
+  it("reads external HTML within a multipart body without downloading named attachments", async () => {
+    thread.messages = [
+      {
+        id: "multipart",
+        payload: {
+          mimeType: "multipart/mixed",
+          parts: [
+            {
+              mimeType: "text/html",
+              body: { attachmentId: "html-body", size: 19 },
+            },
+            {
+              filename: "invoice.pdf",
+              mimeType: "application/pdf",
+              body: { attachmentId: "invoice", size: 200 },
+            },
+          ],
+        },
+      },
+    ];
+    bodies.set("/gmail/v1/users/me/messages/multipart/attachments/html-body", {
+      data: encode("<p>Receipt ready</p>"),
+    });
+    const result = await gmailReadThread.execute(
+      { threadId: "thread-fixture" },
+      context()
+    );
+    expect(result).toMatchObject({
+      thread: {
+        messages: [
+          {
+            body: " Receipt ready ",
+            attachments: [
+              { attachmentId: "invoice", filename: "invoice.pdf", size: 200 },
+            ],
+          },
+        ],
+      },
+    });
+    expect(requests.map((request) => request.path)).toEqual([
+      "/gmail/v1/users/me/threads/thread-fixture",
+      "/gmail/v1/users/me/messages/multipart/attachments/html-body",
+    ]);
+  });
+
+  it("preserves nested inline bodies and excludes named text attachments", async () => {
+    thread.messages = [
+      {
+        id: "nested",
+        payload: {
+          mimeType: "multipart/mixed",
+          parts: [
+            {
+              filename: "notes.txt",
+              mimeType: "text/plain",
+              body: { attachmentId: "notes" },
+            },
+            {
+              mimeType: "multipart/alternative",
+              parts: [
+                {
+                  mimeType: "text/plain",
+                  body: { data: encode("Nested body") },
+                },
+                {
+                  mimeType: "text/html",
+                  body: { data: encode("<p>Alternative body</p>") },
+                },
+              ],
+            },
+          ],
+        },
+      },
+    ];
+    const result = await gmailReadThread.execute(
+      { threadId: "thread-fixture" },
+      context()
+    );
+    expect(result).toMatchObject({
+      thread: { messages: [{ body: "Nested body" }] },
+    });
+    expect(requests).toHaveLength(1);
+  });
+
+  it("surfaces an attachment retrieval failure instead of returning an empty body", async () => {
+    thread.messages = [
+      {
+        id: "missing-body",
+        payload: {
+          mimeType: "text/plain",
+          body: { attachmentId: "unavailable" },
+        },
+      },
+    ];
+    await expect(
+      gmailReadThread.execute({ threadId: "thread-fixture" }, context())
+    ).rejects.toThrow("Unknown fixture path");
+  });
+});
+
+function encode(text: string) {
+  return Buffer.from(text, "utf8").toString("base64url");
+}
+
+function context() {
+  return {
+    ...toolContextFor({ callId: "read-fixture", sessionId: "gmail-fixture" }),
+    getToken: vi
+      .fn<ToolContext["getToken"]>()
+      .mockResolvedValue({ token: "fixture-token" }),
+  } satisfies ToolContext;
+}