diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9021f6596aa..d271b6756af 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ Docs: https://docs.openclaw.ai
 - Auto-reply/WhatsApp/TUI/Web: when a final assistant message is `NO_REPLY` and a messaging tool send succeeded, mirror the delivered messaging-tool text into session-visible assistant output so TUI/Web no longer show `NO_REPLY` placeholders. (#7010) Thanks @Morrowind-Xie.
 - Gateway/Chat: harden `chat.send` inbound message handling by rejecting null bytes, stripping unsafe control characters, and normalizing Unicode to NFC before dispatch. (#8593) Thanks @fr33d3m0n.
 - Gateway/Send: return an actionable error when `send` targets internal-only `webchat`, guiding callers to use `chat.send` or a deliverable channel. (#15703) Thanks @rodrigouroz.
+- Gateway/Agent: reject malformed `agent:`-prefixed session keys (for example, `agent:main`) in `agent` and `agent.identity.get` instead of silently resolving them to the default agent, preventing accidental cross-session routing. (#15707) Thanks @rodrigouroz.
 - Gateway/Security: redact sensitive session/path details from `status` responses for non-admin clients; full details remain available to `operator.admin`. (#8590) Thanks @fr33d3m0n.
 - Agents: return an explicit timeout error reply when an embedded run times out before producing any payloads, preventing silent dropped turns during slow cache-refresh transitions. (#16659) Thanks @liaosvcaf and @vignesh07.
 - Agents/OpenAI: force `store=true` for direct OpenAI Responses/Codex runs to preserve multi-turn server-side conversation state, while leaving proxy/non-OpenAI endpoints unchanged. (#16803) Thanks @mark9232 and @vignesh07.
diff --git a/src/gateway/server-methods/agent.test.ts b/src/gateway/server-methods/agent.test.ts
index 6286e356db0..bdb051e00e5 100644
--- a/src/gateway/server-methods/agent.test.ts
+++ b/src/gateway/server-methods/agent.test.ts
@@ -336,4 +336,54 @@ describe("gateway agent handler", () => {
     expect(call?.message).toBe(BARE_SESSION_RESET_PROMPT);
     expect(call?.sessionId).toBe("reset-session-id");
   });
+
+  it("rejects malformed agent session keys early in agent handler", async () => {
+    mocks.agentCommand.mockClear();
+    const respond = vi.fn();
+
+    await agentHandlers.agent({
+      params: {
+        message: "test",
+        sessionKey: "agent:main",
+        idempotencyKey: "test-malformed-session-key",
+      },
+      respond,
+      context: makeContext(),
+      req: { type: "req", id: "4", method: "agent" },
+      client: null,
+      isWebchatConnect: () => false,
+    });
+
+    expect(mocks.agentCommand).not.toHaveBeenCalled();
+    expect(respond).toHaveBeenCalledWith(
+      false,
+      undefined,
+      expect.objectContaining({
+        message: expect.stringContaining("malformed session key"),
+      }),
+    );
+  });
+
+  it("rejects malformed session keys in agent.identity.get", async () => {
+    const respond = vi.fn();
+
+    await agentHandlers["agent.identity.get"]({
+      params: {
+        sessionKey: "agent:main",
+      },
+      respond,
+      context: makeContext(),
+      req: { type: "req", id: "5", method: "agent.identity.get" },
+      client: null,
+      isWebchatConnect: () => false,
+    });
+
+    expect(respond).toHaveBeenCalledWith(
+      false,
+      undefined,
+      expect.objectContaining({
+        message: expect.stringContaining("malformed session key"),
+      }),
+    );
+  });
 });
diff --git a/src/gateway/server-methods/agent.ts b/src/gateway/server-methods/agent.ts
index 5d4c8773fab..d9c3451ee9b 100644
--- a/src/gateway/server-methods/agent.ts
+++ b/src/gateway/server-methods/agent.ts
@@ -16,7 +16,7 @@ import {
   resolveAgentDeliveryPlan,
   resolveAgentOutboundTarget,
 } from "../../infra/outbound/agent-delivery.js";
-import { normalizeAgentId } from "../../routing/session-key.js";
+import { classifySessionKeyShape, normalizeAgentId } from "../../routing/session-key.js";
 import { defaultRuntime } from "../../runtime.js";
 import { normalizeInputProvenance, type InputProvenance } from "../../sessions/input-provenance.js";
 import { resolveSendPolicy } from "../../sessions/send-policy.js";
@@ -273,6 +273,20 @@ export const agentHandlers: GatewayRequestHandlers = {
       typeof request.sessionKey === "string" && request.sessionKey.trim()
         ? request.sessionKey.trim()
         : undefined;
+    if (
+      requestedSessionKeyRaw &&
+      classifySessionKeyShape(requestedSessionKeyRaw) === "malformed_agent"
+    ) {
+      respond(
+        false,
+        undefined,
+        errorShape(
+          ErrorCodes.INVALID_REQUEST,
+          `invalid agent params: malformed session key "${requestedSessionKeyRaw}"`,
+        ),
+      );
+      return;
+    }
     let requestedSessionKey =
       requestedSessionKeyRaw ??
       resolveExplicitAgentSessionKey({
@@ -601,6 +615,17 @@ export const agentHandlers: GatewayRequestHandlers = {
     const sessionKeyRaw = typeof p.sessionKey === "string" ? p.sessionKey.trim() : "";
     let agentId = agentIdRaw ? normalizeAgentId(agentIdRaw) : undefined;
     if (sessionKeyRaw) {
+      if (classifySessionKeyShape(sessionKeyRaw) === "malformed_agent") {
+        respond(
+          false,
+          undefined,
+          errorShape(
+            ErrorCodes.INVALID_REQUEST,
+            `invalid agent.identity.get params: malformed session key "${sessionKeyRaw}"`,
+          ),
+        );
+        return;
+      }
       const resolved = resolveAgentIdFromSessionKey(sessionKeyRaw);
       if (agentId && resolved !== agentId) {
         respond(
diff --git a/src/gateway/server.agent.gateway-server-agent-a.e2e.test.ts b/src/gateway/server.agent.gateway-server-agent-a.e2e.test.ts
index d783e42d531..ed6b9d4cce2 100644
--- a/src/gateway/server.agent.gateway-server-agent-a.e2e.test.ts
+++ b/src/gateway/server.agent.gateway-server-agent-a.e2e.test.ts
@@ -285,6 +285,20 @@ describe("gateway server agent", () => {
     expect(spy).not.toHaveBeenCalled();
   });
 
+  test("agent rejects malformed agent-prefixed session keys", async () => {
+    setRegistry(defaultRegistry);
+    const res = await rpcReq(ws, "agent", {
+      message: "hi",
+      sessionKey: "agent:main",
+      idempotencyKey: "idem-agent-malformed-key",
+    });
+    expect(res.ok).toBe(false);
+    expect(res.error?.message).toContain("malformed session key");
+
+    const spy = vi.mocked(agentCommand);
+    expect(spy).not.toHaveBeenCalled();
+  });
+
   test("agent forwards accountId to agentCommand", async () => {
     setRegistry(defaultRegistry);
     testState.allowFrom = ["+1555"];