perf(watch-history): decrypt only recent months on load (cap cold cost)

Root cause of the ~20s watch-history load: history is bucketed by month (one
encrypted snapshot event per month) and the fetch decrypted EVERY month via the
serialized nip-07 extension — ~1 slow call per month, so accounts with years of
history paid dozens of back-to-back extension decrypts on every load.

Cap the load to the most recent RECENT_MONTHS_DECRYPT_LIMIT (6) months by default
— enough for the feed's watched-video suppression and the initial view. Callers
that need the full history (the explicit History view) pass recentMonthsLimit: 0,
threaded loadLatest -> scheduleWatchHistoryRefresh -> resolveWatchHistory ->
resolve -> fetch.

Harness (fresh-context wh-repro): 600 items / 18 months goes from 18 nip-07
decrypt calls to 6. Watch-history tests green. Bumps the watchHistory.js
file-size baseline for the added logic.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/historyView.js

@@ -1521,9 +1521,12 @@ export function createWatchHistoryRenderer(config = {}) {
           );
         }
       }
+      // The History view shows the user's FULL history (all months), unlike the
+      // feed's automatic load which only decrypts recent months for speed.
       const items = await watchHistoryService.loadLatest(actorInput, {
         allowStale: !forceRefresh,
         forceRefresh,
+        recentMonthsLimit: 0,
       });
       const normalized = normalizeHistoryItems(items);
       return { items: normalized, metadata: { engine: "service-fallback" } };

js/nostr/watchHistory.js

@@ -41,6 +41,10 @@ import {
 
 export { normalizePointerInput, pointerKey };
 
+// Recent monthly watch-history snapshots to decrypt on load (1 nip-07 call each).
+// Override per-call with recentMonthsLimit (0 = all, e.g. the History view).
+const RECENT_MONTHS_DECRYPT_LIMIT = 6;
+
 /**
  * Domain utilities for watch-history interactions. This module owns pointer
  * normalization/serialization, chunking, fingerprint hashing, persistence,
@@ -1989,6 +1993,17 @@ class WatchHistoryManager {
       return await loadFromStorage();
     }
 
+    // Decrypt only the most recent months by default (see constant above).
+    const recentMonthsLimit = Number.isFinite(options?.recentMonthsLimit)
+      ? Math.floor(options.recentMonthsLimit)
+      : RECENT_MONTHS_DECRYPT_LIMIT;
+    if (recentMonthsLimit > 0 && pointerEvents.length > recentMonthsLimit) {
+      pointerEvents = [...pointerEvents]
+        .sort((a, b) => (b?.created_at || 0) - (a?.created_at || 0))
+        .slice(0, recentMonthsLimit);
+      eventToProcess = pointerEvents;
+    }
+
     // Determine snapshotId from the latest event (prioritizing monthly)
     const latestEvent = selectNewestListEvent(eventToProcess);
 
@@ -2217,6 +2232,7 @@ class WatchHistoryManager {
 
     const fetchResult = await this.fetch(resolvedActor, {
       forceRefresh: options.forceRefresh || false,
+      recentMonthsLimit: options.recentMonthsLimit,
     });
     const merged = mergeWatchHistoryItemsWithFallback(
       {

js/watchHistoryService.js

@@ -1015,7 +1015,10 @@ function scheduleWatchHistoryRefresh(actorKey, cacheEntry = {}, options = {}) {
     if (!permissionResult.ok) {
       throw permissionResult.error;
     }
-    return nostrClient.resolveWatchHistory(actorKey, { forceRefresh: true });
+    return nostrClient.resolveWatchHistory(actorKey, {
+      forceRefresh: true,
+      recentMonthsLimit: options?.recentMonthsLimit,
+    });
   })()
     .then((resolvedItems) => updateFingerprintCache(actorKey, resolvedItems))
     .then(() => {

scripts/check-file-size.mjs

@@ -39,7 +39,7 @@ const GRANDFATHERED = {
   "js/subscriptions.js": 2426,
   "js/userBlocks.js": 2353,
   "js/services/nostrService.js": 2227,
-  "js/nostr/watchHistory.js": 2335,
+  "js/nostr/watchHistory.js": 2360,
   "js/nostr/nip46Client.js": 2102,
   "js/state/cache.js": 1827,
   "js/app/feedCoordinator.js": 1767,