fetch keys as part of afterSyncCompleted step

remove needsAfterSyncCompleted step as well, performance difference
should be neglible

src/matrix/Sync.js

@@ -47,10 +47,8 @@ function timelineIsEmpty(roomResponse) {
  * const changes = await room.writeSync(roomResponse, isInitialSync, preparation, syncTxn);
  * // applies and emits changes once syncTxn is committed
  * room.afterSync(changes);
- * if (room.needsAfterSyncCompleted(changes)) {
  * // can do network requests
  * await room.afterSyncCompleted(changes);
- * }
  * ```
  */
 export class Sync {
@@ -163,13 +161,9 @@ export class Sync {
                 await log.wrap("session", log => this._session.afterSyncCompleted(sessionChanges, isCatchupSync, log), log.level.Detail);
             } catch (err) {} // error is logged, but don't fail sessionPromise
         })();
-
-        const roomsNeedingAfterSyncCompleted = roomStates.filter(rs => {
-            return rs.room.needsAfterSyncCompleted(rs.changes);
-        });
-        const roomsPromises = roomsNeedingAfterSyncCompleted.map(async rs => {
+        const roomsPromises = roomStates.map(async rs => {
             try {
-                await log.wrap("room", log => rs.room.afterSyncCompleted(rs.changes, log), log.level.Detail);
+                await rs.room.afterSyncCompleted(rs.changes, log);
             } catch (err) {} // error is logged, but don't fail roomsPromises
         });
         // run everything in parallel,

src/matrix/e2ee/RoomEncryption.js

@@ -557,15 +557,17 @@ class BatchDecryptionResult {
         this._roomEncryption = roomEncryption;
     }
 
-    applyToEntries(entries) {
+    applyToEntries(entries, callback = undefined) {
         for (const entry of entries) {
             const result = this.results.get(entry.id);
             if (result) {
                 entry.setDecryptionResult(result);
+                callback?.(entry);
             } else {
                 const error = this.errors.get(entry.id);
                 if (error) {
                     entry.setDecryptionError(error);
+                    callback?.(entry);
                 }
             }
         }
@@ -577,6 +579,15 @@ class BatchDecryptionResult {
         return this._roomEncryption._verifyDecryptionResults(Array.from(this.results.values()), txn);
     }
 
+    get hasUnverifiedSenders() {
+        for (const r of this.results.values()) {
+            if (r.isVerificationUnknown) {
+                return true;
+            }
+        }
+        return false;
+    }
+
     /** Verify any decryption results for which we could not find a device when
      *  calling `verifyKnownSenders` prior, by fetching them from the homeserver.
      *  @returns {Promise<BatchDecryptionResult>} the results for which we found a device */

src/matrix/room/Room.js

@@ -189,6 +189,7 @@ export class Room extends BaseRoom {
             heroChanges,
             powerLevelsEvent,
             encryptionChanges,
+            decryption
         };
     }
 
@@ -291,19 +292,35 @@ export class Room extends BaseRoom {
         }
     }
 
-    needsAfterSyncCompleted({encryptionChanges}) {
-        return encryptionChanges?.shouldFlush;
-    }
-
     /**
      * Only called if the result of writeSync had `needsAfterSyncCompleted` set.
      * Can be used to do longer running operations that resulted from the last sync,
      * like network operations.
      */
-    async afterSyncCompleted(changes, log) {
-        log.set("id", this.id);
-        if (this._roomEncryption) {
-            await this._roomEncryption.flushPendingRoomKeyShares(this._hsApi, null, log);
+    async afterSyncCompleted({encryptionChanges, decryption, newEntries, updatedEntries}, log) {
+        const shouldFlushKeys = encryptionChanges?.shouldFlush;
+        const shouldFetchUnverifiedSenders = this._isTimelineOpen && decryption?.hasUnverifiedSenders;
+        // only log rooms where we actually do something
+        if (shouldFlushKeys || shouldFetchUnverifiedSenders) {
+            log.wrap({l: "room", id: this.id}, async log => {
+                const promises = [];
+                if (shouldFlushKeys) {
+                    promises.push(this._roomEncryption.flushPendingRoomKeyShares(this._hsApi, null, log));
+                }
+                if (shouldFetchUnverifiedSenders) {
+                    const promise = (async () => {
+                        const newlyVerifiedDecryption = await decryption.fetchAndVerifyRemainingSenders(this._hsApi, log);
+                        const verifiedEntries = [];
+                        const updateCallback = entry => verifiedEntries.push(entry);
+                        newlyVerifiedDecryption.applyToEntries(newEntries, updateCallback);
+                        newlyVerifiedDecryption.applyToEntries(updated, updateCallback);
+                        // TODO: update _observedEvents here as well?
+                        this._timeline.replaceEntries(verifiedEntries);
+                    });
+                    promises.push(promise);
+                }
+                await Promise.all(promises);
+            });
         }
     }