diff --git a/src/discord/monitor/message-handler.process.ts b/src/discord/monitor/message-handler.process.ts
index 9b97d70b9..14616420f 100644
--- a/src/discord/monitor/message-handler.process.ts
+++ b/src/discord/monitor/message-handler.process.ts
@@ -557,14 +557,12 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
     storePath,
     sessionKey: ctxPayload.SessionKey ?? route.sessionKey,
     ctx: ctxPayload,
-    updateLastRoute: isDirectMessage
-      ? {
-          sessionKey: route.mainSessionKey,
-          channel: "discord",
-          to: `user:${author.id}`,
-          accountId: route.accountId,
-        }
-      : undefined,
+    updateLastRoute: {
+      sessionKey: ctxPayload.SessionKey ?? route.sessionKey,
+      channel: "discord",
+      to: effectiveTo,
+      accountId: route.accountId,
+    },
     onRecordError: (err) => {
       logVerbose(`discord: failed updating session meta: ${String(err)}`);
     },
diff --git a/src/routing/session-key.continuity.test.ts b/src/routing/session-key.continuity.test.ts
new file mode 100644
index 000000000..dc6fa6a05
--- /dev/null
+++ b/src/routing/session-key.continuity.test.ts
@@ -0,0 +1,70 @@
+import { describe, it, expect } from "vitest";
+import { buildAgentSessionKey } from "./resolve-route.js";
+
+describe("Discord Session Key Continuity", () => {
+  const agentId = "main";
+  const channel = "discord";
+  const accountId = "default";
+
+  it("generates distinct keys for DM vs Channel (dmScope=main)", () => {
+    // Scenario: Default config (dmScope=main)
+    const dmKey = buildAgentSessionKey({
+      agentId,
+      channel,
+      accountId,
+      peer: { kind: "direct", id: "user123" },
+      dmScope: "main",
+    });
+
+    const groupKey = buildAgentSessionKey({
+      agentId,
+      channel,
+      accountId,
+      peer: { kind: "channel", id: "channel456" },
+      dmScope: "main",
+    });
+
+    expect(dmKey).toBe("agent:main:main");
+    expect(groupKey).toBe("agent:main:discord:channel:channel456");
+    expect(dmKey).not.toBe(groupKey);
+  });
+
+  it("generates distinct keys for DM vs Channel (dmScope=per-peer)", () => {
+    // Scenario: Multi-user bot config
+    const dmKey = buildAgentSessionKey({
+      agentId,
+      channel,
+      accountId,
+      peer: { kind: "direct", id: "user123" },
+      dmScope: "per-peer",
+    });
+
+    const groupKey = buildAgentSessionKey({
+      agentId,
+      channel,
+      accountId,
+      peer: { kind: "channel", id: "channel456" },
+      dmScope: "per-peer",
+    });
+
+    expect(dmKey).toBe("agent:main:direct:user123");
+    expect(groupKey).toBe("agent:main:discord:channel:channel456");
+    expect(dmKey).not.toBe(groupKey);
+  });
+
+  it("handles empty/invalid IDs safely without collision", () => {
+    // If ID is missing, does it collide?
+    const missingIdKey = buildAgentSessionKey({
+      agentId,
+      channel,
+      accountId,
+      peer: { kind: "channel", id: "" }, // Empty string
+      dmScope: "main",
+    });
+
+    expect(missingIdKey).toContain("unknown");
+    
+    // Should still be distinct from main
+    expect(missingIdKey).not.toBe("agent:main:main");
+  });
+});