diff --git a/src/config/sessions/session-key.ts b/src/config/sessions/session-key.ts
index 70c1eba0a8b..1443be30630 100644
--- a/src/config/sessions/session-key.ts
+++ b/src/config/sessions/session-key.ts
@@ -1,5 +1,5 @@
 import type { MsgContext } from "../../auto-reply/templating.js";
-import { normalizeChatType } from "../../channels/chat-type.js";
+import { normalizeExplicitDiscordSessionKey } from "../../discord/session-key-normalization.js";
 import {
   buildAgentMainSessionKey,
   DEFAULT_AGENT_ID,
@@ -29,24 +29,7 @@ export function deriveSessionKey(scope: SessionScope, ctx: MsgContext) {
 export function resolveSessionKey(scope: SessionScope, ctx: MsgContext, mainKey?: string) {
   const explicit = ctx.SessionKey?.trim();
   if (explicit) {
-    let normalized = explicit.toLowerCase();
-    if (normalizeChatType(ctx.ChatType) === "direct") {
-      normalized = normalized.replace(/^(agent:[^:]+:discord:)dm:/, "$1direct:");
-      const match = normalized.match(/^((?:agent:[^:]+:)?)discord:channel:([^:]+)$/);
-      if (match) {
-        const from = (ctx.From ?? "").trim().toLowerCase();
-        const senderId = (ctx.SenderId ?? "").trim().toLowerCase();
-        const fromDiscordId =
-          from.startsWith("discord:") && !from.includes(":channel:") && !from.includes(":group:")
-            ? from.slice("discord:".length)
-            : "";
-        const directId = senderId || fromDiscordId;
-        if (directId && directId === match[2]) {
-          normalized = `${match[1]}discord:direct:${match[2]}`;
-        }
-      }
-    }
-    return normalized;
+    return normalizeExplicitDiscordSessionKey(explicit, ctx);
   }
   const raw = deriveSessionKey(scope, ctx);
   if (scope === "global") {
diff --git a/src/discord/session-key-normalization.test.ts b/src/discord/session-key-normalization.test.ts
new file mode 100644
index 00000000000..22066c3da95
--- /dev/null
+++ b/src/discord/session-key-normalization.test.ts
@@ -0,0 +1,34 @@
+import { describe, expect, it } from "vitest";
+import { normalizeExplicitDiscordSessionKey } from "./session-key-normalization.js";
+
+describe("normalizeExplicitDiscordSessionKey", () => {
+  it("rewrites legacy discord:dm keys for direct chats", () => {
+    expect(
+      normalizeExplicitDiscordSessionKey("agent:fina:discord:dm:123456", {
+        ChatType: "direct",
+        From: "discord:123456",
+        SenderId: "123456",
+      }),
+    ).toBe("agent:fina:discord:direct:123456");
+  });
+
+  it("rewrites phantom discord:channel keys when sender matches", () => {
+    expect(
+      normalizeExplicitDiscordSessionKey("discord:channel:123456", {
+        ChatType: "direct",
+        From: "discord:123456",
+        SenderId: "123456",
+      }),
+    ).toBe("discord:direct:123456");
+  });
+
+  it("leaves non-direct channel keys unchanged", () => {
+    expect(
+      normalizeExplicitDiscordSessionKey("agent:fina:discord:channel:123456", {
+        ChatType: "channel",
+        From: "discord:channel:123456",
+        SenderId: "789",
+      }),
+    ).toBe("agent:fina:discord:channel:123456");
+  });
+});
diff --git a/src/discord/session-key-normalization.ts b/src/discord/session-key-normalization.ts
new file mode 100644
index 00000000000..05a48c7e06b
--- /dev/null
+++ b/src/discord/session-key-normalization.ts
@@ -0,0 +1,27 @@
+import type { MsgContext } from "../auto-reply/templating.js";
+import { normalizeChatType } from "../channels/chat-type.js";
+
+export function normalizeExplicitDiscordSessionKey(
+  sessionKey: string,
+  ctx: Pick<MsgContext, "ChatType" | "From" | "SenderId">,
+): string {
+  let normalized = sessionKey.trim().toLowerCase();
+  if (normalizeChatType(ctx.ChatType) !== "direct") {
+    return normalized;
+  }
+
+  normalized = normalized.replace(/^(agent:[^:]+:discord:)dm:/, "$1direct:");
+  const match = normalized.match(/^((?:agent:[^:]+:)?)discord:channel:([^:]+)$/);
+  if (!match) {
+    return normalized;
+  }
+
+  const from = (ctx.From ?? "").trim().toLowerCase();
+  const senderId = (ctx.SenderId ?? "").trim().toLowerCase();
+  const fromDiscordId =
+    from.startsWith("discord:") && !from.includes(":channel:") && !from.includes(":group:")
+      ? from.slice("discord:".length)
+      : "";
+  const directId = senderId || fromDiscordId;
+  return directId && directId === match[2] ? `${match[1]}discord:direct:${match[2]}` : normalized;
+}