fix(library): resolve main-thread UI freeze and process kill data loss via OPFS payload capping, yield throttling, and UI batching

docker/frontend/src/engine/library.ts

@@ -45,7 +45,7 @@ const LANES = 4;
 // How often the walk's position is written down, in the same seconds as the
 // catalogue is read back on: the position is the whole of what the walk has found
 // and not read, and writing it is a string of a few megabytes on a long roll.
-const WALK_MS = 2000;
+const WALK_MS = 5000;
 // How often the screen is told how far the reading has come: the column is
 // rebuilt out of the count, and a rebuild a frame is a reading that spends its
 // time drawing itself. Five times a second is a counter that moves to the eye
@@ -834,11 +834,12 @@ export async function scanFolder(
     if (at - wroteAt < WALK_MS) return;
     wroteAt = at;
     const held = [...inHand, ...batch.map(pathOf)];
+    const savedEntries = entries.slice(0, 500).map((e) => e.rel);
     await saveWalk(
       folder.name,
       [...tree.walked],
       tree.pending.map((p) => p.rel),
-      [...held, ...entries.map((e) => e.rel)],
+      [...held, ...savedEntries],
       held.length,
       progress
     );
@@ -962,11 +963,12 @@ export async function scanFolder(
 
       // Micro-yield to the browser main thread event loop so scanning never blocks UI rendering or user interactions
       processed++;
-      if (processed % 12 === 0) {
+      if (processed % 3 === 0) {
         await new Promise((resolve) => setTimeout(resolve, 0));
       }
     }
     await Promise.all(lanes);
+    await flush();
   };
 
   // How many of the frames in hand were counted by the reading that handed them