playlists: promise the count that holds when nothing compresses

The ceiling is 1200 tracks on a library that repeats and 660 on one that
never does; the message said 1000, which would send a reader back into the
wall at 660. It says 500, measured at both ends.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/packages/meshbay-hub/tests/harness/playlist_store_probe.py b/packages/meshbay-hub/tests/harness/playlist_store_probe.py
index 83c00ad..6421426 100755
--- a/packages/meshbay-hub/tests/harness/playlist_store_probe.py
+++ b/packages/meshbay-hub/tests/harness/playlist_store_probe.py
@@ -395,7 +395,31 @@ function fakeNode() {
                                 bodyKind('measure'), USER, key);
       sizes[n] = sealed.length;
     }
-    steps.push({ step: 'what a playlist costs sealed', sizes });
+
+    // The same, with nothing to compress. Fourteen words of vocabulary is a
+    // library that repeats itself; a real one does not, and deflate's whole
+    // saving here comes from repetition. This is the pessimistic bound, and the
+    // number a reader is told has to sit under *it*, not under the friendly one
+    // — the two differ by enough to matter.
+    const noise = (n) => [...crypto.getRandomValues(new Uint8Array(n))]
+      .map((b) => 'abcdefghijklmnopqrstuvwxyz '[b % 27]).join('');
+    const diverseTrack = (i) => {
+      const artist = noise(18);
+      const album = noise(22);
+      const title = noise(26);
+      return { id: hex(16), g: 'g1', hv: 1, n: `${i % 20} - ${title}.flac`,
+               s: 30000000 + i, p: `${artist}/${album}`, t: title, a: artist,
+               b: album, d: 180 + (i % 300), tn: (i % 20) + 1 };
+    };
+    const diverse = {};
+    for (const n of [100, 500, 1000]) {
+      const tracks = [];
+      for (let i = 0; i < n; i++) tracks.push(diverseTrack(i));
+      const sealed = await seal({ v: 1, id: 'measure', rev: 1, device: 'aaa', tracks },
+                                bodyKind('measure'), USER, key);
+      diverse[n] = sealed.length;
+    }
+    steps.push({ step: 'what a playlist costs sealed', sizes, diverse });
 
     // ── a playlist too large for one frame is named, not swallowed ────────
     //