diff --git a/extensions/matrix/src/matrix/monitor/events.test.ts b/extensions/matrix/src/matrix/monitor/events.test.ts
index 4f264d0bde4..c3a73ba9ba8 100644
--- a/extensions/matrix/src/matrix/monitor/events.test.ts
+++ b/extensions/matrix/src/matrix/monitor/events.test.ts
@@ -65,6 +65,7 @@ function createHarness(params?: {
       async (roomId: string) =>
         params?.joinedMembersByRoom?.[roomId] ?? ["@bot:example.org", "@alice:example.org"],
     ),
+    getJoinedRooms: vi.fn(async () => Object.keys(params?.joinedMembersByRoom ?? {})),
     ...(params?.cryptoAvailable === false
       ? {}
       : {
@@ -346,6 +347,50 @@ describe("registerMatrixMonitorEvents verification routing", () => {
     });
   });
 
+  it("posts SAS notices from summary updates using the active strict DM when room mapping is missing", async () => {
+    const { sendMessage, verificationSummaryListener } = createHarness({
+      joinedMembersByRoom: {
+        "!dm-active:example.org": ["@alice:example.org", "@bot:example.org"],
+      },
+    });
+    if (!verificationSummaryListener) {
+      throw new Error("verification.summary listener was not registered");
+    }
+
+    verificationSummaryListener({
+      id: "verification-unmapped",
+      otherUserId: "@alice:example.org",
+      isSelfVerification: false,
+      initiatedByMe: false,
+      phase: 3,
+      phaseName: "started",
+      pending: true,
+      methods: ["m.sas.v1"],
+      canAccept: false,
+      hasSas: true,
+      sas: {
+        decimal: [4321, 8765, 2109],
+        emoji: [
+          ["🚀", "Rocket"],
+          ["🦋", "Butterfly"],
+          ["📕", "Book"],
+        ],
+      },
+      hasReciprocateQr: false,
+      completed: false,
+      createdAt: new Date("2026-02-25T21:42:54.000Z").toISOString(),
+      updatedAt: new Date("2026-02-25T21:42:55.000Z").toISOString(),
+    });
+
+    await vi.waitFor(() => {
+      expect(sendMessage).toHaveBeenCalledTimes(1);
+    });
+    const roomId = (sendMessage.mock.calls[0]?.[0] ?? "") as string;
+    const body = getSentNoticeBody(sendMessage, 0);
+    expect(roomId).toBe("!dm-active:example.org");
+    expect(body).toContain("SAS decimal: 4321 8765 2109");
+  });
+
   it("retries SAS notice lookup when start arrives before SAS payload is available", async () => {
     vi.useFakeTimers();
     const verifications: Array<{
diff --git a/extensions/matrix/src/matrix/monitor/verification-events.ts b/extensions/matrix/src/matrix/monitor/verification-events.ts
index 0147607f0ce..0e5d3573652 100644
--- a/extensions/matrix/src/matrix/monitor/verification-events.ts
+++ b/extensions/matrix/src/matrix/monitor/verification-events.ts
@@ -1,3 +1,4 @@
+import { inspectMatrixDirectRooms } from "../direct-management.js";
 import { isStrictDirectRoom } from "../direct-room.js";
 import type { MatrixClient } from "../sdk.js";
 import type { MatrixRawEvent } from "./types.js";
@@ -322,18 +323,32 @@ export function createMatrixVerificationEventRouter(params: {
     }
   }
 
-  function resolveSummaryRoomId(summary: MatrixVerificationSummaryLike): string | null {
-    return (
+  async function resolveSummaryRoomId(
+    summary: MatrixVerificationSummaryLike,
+  ): Promise<string | null> {
+    const mappedRoomId =
       trimMaybeString(summary.roomId) ??
       trimMaybeString(
         summary.transactionId ? verificationFlowRooms.get(summary.transactionId) : null,
       ) ??
-      trimMaybeString(verificationFlowRooms.get(summary.id))
-    );
+      trimMaybeString(verificationFlowRooms.get(summary.id));
+    if (mappedRoomId) {
+      return mappedRoomId;
+    }
+
+    const remoteUserId = trimMaybeString(summary.otherUserId);
+    if (!remoteUserId) {
+      return null;
+    }
+    const inspection = await inspectMatrixDirectRooms({
+      client: params.client,
+      remoteUserId,
+    }).catch(() => null);
+    return trimMaybeString(inspection?.activeRoomId);
   }
 
   async function routeVerificationSummary(summary: MatrixVerificationSummaryLike): Promise<void> {
-    const roomId = resolveSummaryRoomId(summary);
+    const roomId = await resolveSummaryRoomId(summary);
     if (!roomId || !isActiveVerificationSummary(summary)) {
       return;
     }