fix: harden Matrix verification fallback paths

extensions/matrix/src/matrix/sdk.ts

@@ -372,7 +372,7 @@ export class MatrixClient {
       trustOwnDeviceAfterSas: async (deviceId: string) => {
         const crypto = this.client.getCrypto() as MatrixCryptoBootstrapApi | undefined;
         if (typeof crypto?.crossSignDevice !== "function") {
-          throw new Error("Matrix crypto backend does not support cross-signing devices");
+          return;
         }
         await crypto.crossSignDevice(deviceId);
       },

extensions/matrix/src/matrix/sdk/verification-manager.test.ts

@@ -188,6 +188,45 @@ describe("MatrixVerificationManager", () => {
     expect(secondSummary.chosenMethod).toBe("m.sas.v1");
   });
 
+  it("reuses the tracked id when the other device id is populated later", () => {
+    const manager = new MatrixVerificationManager();
+    const first = new MockVerificationRequest({
+      transactionId: "txn-device-later",
+      phase: VerificationPhase.Requested,
+    });
+    const second = new MockVerificationRequest({
+      transactionId: "txn-device-later",
+      phase: VerificationPhase.Ready,
+      otherDeviceId: "DEVICE_LATER",
+      pending: false,
+    });
+
+    const firstSummary = manager.trackVerificationRequest(first);
+    const secondSummary = manager.trackVerificationRequest(second);
+
+    expect(secondSummary.id).toBe(firstSummary.id);
+    expect(secondSummary.otherDeviceId).toBe("DEVICE_LATER");
+    expect(manager.listVerifications()).toHaveLength(1);
+  });
+
+  it("keeps separate sessions when stable other device ids differ", () => {
+    const manager = new MatrixVerificationManager();
+    const first = new MockVerificationRequest({
+      transactionId: "txn-different-devices",
+      otherDeviceId: "DEVICE_A",
+    });
+    const second = new MockVerificationRequest({
+      transactionId: "txn-different-devices",
+      otherDeviceId: "DEVICE_B",
+    });
+
+    const firstSummary = manager.trackVerificationRequest(first);
+    const secondSummary = manager.trackVerificationRequest(second);
+
+    expect(secondSummary.id).not.toBe(firstSummary.id);
+    expect(manager.listVerifications()).toHaveLength(2);
+  });
+
   it("does not overwrite a different verification request with a colliding transaction ID", async () => {
     const manager = new MatrixVerificationManager();
     const first = new MockVerificationRequest({

extensions/matrix/src/matrix/sdk/verification-manager.ts

@@ -204,12 +204,16 @@ export class MatrixVerificationManager {
       leftIdentity.transactionId === rightIdentity.transactionId &&
       leftIdentity.roomId === rightIdentity.roomId &&
       leftIdentity.otherUserId === rightIdentity.otherUserId &&
-      leftIdentity.otherDeviceId === rightIdentity.otherDeviceId &&
+      this.isSameOptionalIdentityValue(leftIdentity.otherDeviceId, rightIdentity.otherDeviceId) &&
       leftIdentity.isSelfVerification === rightIdentity.isSelfVerification &&
       leftIdentity.initiatedByMe === rightIdentity.initiatedByMe
     );
   }
 
+  private isSameOptionalIdentityValue(left: string, right: string): boolean {
+    return left === "" || right === "" || left === right;
+  }
+
   private pruneVerificationSessions(nowMs: number): void {
     for (const [id, session] of this.verificationSessions) {
       const phase = this.readVerificationPhase(session.request, -1);