perf(library): a drive is walked with its position written every five seconds

docker/frontend/src/engine/library.ts

@@ -55,8 +55,16 @@ const FLUSH_MS = 400;
 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 = 1000;
+// and not read, and writing it is a string of a few megabytes on a long roll —
+// on the hundred-and-forty-thousand-frame roll of a whole drive it is that many
+// paths joined, stringified and encoded, some twelve to eighteen megabytes of
+// rubbish the page drops every time, which at a second apiece is what drives a
+// reading of a drive to the better part of two gigabytes and shuts the tab. Five
+// seconds is a fifth of that rubbish and a position the reading catches up to on
+// its own: a frame it has already listed is one it does not read again.
+// ponytail: ceiling is the write itself, still megabytes; cut `HEAD_BYTES` or
+// write the position as a delta if five seconds is not enough.
+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