diff --git a/extensions/googlechat/src/monitor.test.ts b/extensions/googlechat/src/monitor.test.ts
index 5604671ad..c03831021 100644
--- a/extensions/googlechat/src/monitor.test.ts
+++ b/extensions/googlechat/src/monitor.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from "vitest";
 
-import { isSenderAllowed } from "./monitor.js";
+import { isSenderAllowed, resolveSpaceType } from "./monitor.js";
 
 describe("isSenderAllowed", () => {
   it("matches allowlist entries with users/<email>", () => {
@@ -25,3 +25,85 @@ describe("isSenderAllowed", () => {
     );
   });
 });
+
+describe("resolveSpaceType", () => {
+  describe("modern spaceType field", () => {
+    it("detects DIRECT_MESSAGE as DM", () => {
+      const result = resolveSpaceType({ spaceType: "DIRECT_MESSAGE" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+
+    it("detects SPACE as group", () => {
+      const result = resolveSpaceType({ spaceType: "SPACE" });
+      expect(result.spaceType).toBe("SPACE");
+      expect(result.isGroup).toBe(true);
+    });
+
+    it("detects GROUP_CHAT as group", () => {
+      const result = resolveSpaceType({ spaceType: "GROUP_CHAT" });
+      expect(result.spaceType).toBe("GROUP_CHAT");
+      expect(result.isGroup).toBe(true);
+    });
+
+    it("handles lowercase spaceType", () => {
+      const result = resolveSpaceType({ spaceType: "direct_message" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+  });
+
+  describe("deprecated type field fallback", () => {
+    it("maps legacy DM to DIRECT_MESSAGE", () => {
+      const result = resolveSpaceType({ type: "DM" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+
+    it("maps legacy ROOM to SPACE", () => {
+      const result = resolveSpaceType({ type: "ROOM" });
+      expect(result.spaceType).toBe("SPACE");
+      expect(result.isGroup).toBe(true);
+    });
+
+    it("handles lowercase legacy type", () => {
+      const result = resolveSpaceType({ type: "dm" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+  });
+
+  describe("field priority", () => {
+    it("prefers modern spaceType over deprecated type", () => {
+      const result = resolveSpaceType({ spaceType: "SPACE", type: "DM" });
+      expect(result.spaceType).toBe("SPACE");
+      expect(result.isGroup).toBe(true);
+    });
+
+    it("falls back to type only when spaceType is missing", () => {
+      const result = resolveSpaceType({ type: "DM" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+
+    it("falls back to type when spaceType is empty string", () => {
+      const result = resolveSpaceType({ spaceType: "", type: "DM" });
+      expect(result.spaceType).toBe("DIRECT_MESSAGE");
+      expect(result.isGroup).toBe(false);
+    });
+  });
+
+  describe("edge cases", () => {
+    it("treats empty space as group", () => {
+      const result = resolveSpaceType({});
+      expect(result.spaceType).toBe("");
+      expect(result.isGroup).toBe(true);
+    });
+
+    it("treats unknown spaceType as group", () => {
+      const result = resolveSpaceType({ spaceType: "UNKNOWN_TYPE" });
+      expect(result.spaceType).toBe("UNKNOWN_TYPE");
+      expect(result.isGroup).toBe(true);
+    });
+  });
+});
diff --git a/extensions/googlechat/src/monitor.ts b/extensions/googlechat/src/monitor.ts
index 74ea57d68..b87be5a59 100644
--- a/extensions/googlechat/src/monitor.ts
+++ b/extensions/googlechat/src/monitor.ts
@@ -297,6 +297,27 @@ function normalizeUserId(raw?: string | null): string {
   return trimmed.replace(/^users\//i, "").toLowerCase();
 }
 
+/**
+ * Resolves the space type from Google Chat space object.
+ * Normalizes to modern 'spaceType' format with fallback for deprecated 'type' field.
+ */
+export function resolveSpaceType(space: { type?: string; spaceType?: string }): {
+  spaceType: string;
+  isGroup: boolean;
+} {
+  // Normalize to modern 'spaceType' format
+  let spaceType = (space.spaceType ?? "").toUpperCase();
+
+  // @deprecated fallback: map legacy 'type' to modern values
+  if (!spaceType && space.type) {
+    const legacyType = space.type.toUpperCase();
+    spaceType = legacyType === "DM" ? "DIRECT_MESSAGE" : "SPACE";
+  }
+
+  const isGroup = spaceType !== "DIRECT_MESSAGE";
+  return { spaceType, isGroup };
+}
+
 export function isSenderAllowed(
   senderId: string,
   senderEmail: string | undefined,
@@ -388,16 +409,7 @@ async function processMessageWithPipeline(params: {
   const spaceId = space.name ?? "";
   if (!spaceId) return;
 
-  // Normalize to modern 'spaceType' format
-  let spaceType = (space.spaceType ?? "").toUpperCase();
-
-  // @deprecated fallback: map legacy 'type' to modern values
-  if (!spaceType && space.type) {
-    const legacyType = space.type.toUpperCase();
-    spaceType = legacyType === "DM" ? "DIRECT_MESSAGE" : "SPACE";
-  }
-
-  const isGroup = spaceType !== "DIRECT_MESSAGE";
+  const { isGroup } = resolveSpaceType(space);
   const sender = message.sender ?? event.user;
   const senderId = sender?.name ?? "";
   const senderName = sender?.displayName ?? "";