From 053c2680cee307dc1f52302c9d8b8c48dae45fcd Mon Sep 17 00:00:00 2001
From: Will Cohen <willcohen@users.noreply.github.com>
Date: Wed, 26 Aug 2026 14:29:59 -0400
Subject: [PATCH] Budget the worker decode cache by bytes

---
 CHANGELOG.md                            |  5 +++++
 packages/backproj/src/wasmts-handler.ts | 18 ++++++++++++++----
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6851ae6..73f3c70 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Change Log
 
+## [Unreleased]
+
+### Changed
+- The worker decode cache is budgeted by input bytes instead of entry count
+
 ## [0.0.5] - 2026-08-26
 
 ### Added
diff --git a/packages/backproj/src/wasmts-handler.ts b/packages/backproj/src/wasmts-handler.ts
index 7faeea1..6920f9b 100644
--- a/packages/backproj/src/wasmts-handler.ts
+++ b/packages/backproj/src/wasmts-handler.ts
@@ -72,14 +72,17 @@ let projHandler: any = null;
  * an FNV-1a hash and re-decode on mismatch. Cached features are shared
  * across chain calls: everything downstream reads them without
  * mutating (see groupDecodedFeatures).
+ *
+ * Budgeted by input bytes; decoded output runs ~10x the PBF.
  */
-const DECODE_CACHE_MAX = 16;
+const DECODE_CACHE_MAX_BYTES = 2 * 1024 * 1024;
 interface DecodeCacheEntry {
   byteLength: number;
   hash: number;
   features: DecodedFeature[];
 }
 const decodeCache = new Map<string, DecodeCacheEntry>();
+let decodeCacheBytes = 0;
 
 function fnv1a(bytes: Uint8Array): number {
   let h = 0x811c9dc5;
@@ -106,10 +109,17 @@ function decodedFeaturesFor(
     return entry.features;
   }
   const features = decodeTile(data, coord);
-  decodeCache.delete(key);
+  const stale = decodeCache.get(key);
+  if (stale) {
+    decodeCache.delete(key);
+    decodeCacheBytes -= stale.byteLength;
+  }
   decodeCache.set(key, { byteLength: bytes.length, hash, features });
-  if (decodeCache.size > DECODE_CACHE_MAX) {
-    decodeCache.delete(decodeCache.keys().next().value!);
+  decodeCacheBytes += bytes.length;
+  while (decodeCacheBytes > DECODE_CACHE_MAX_BYTES && decodeCache.size > 1) {
+    const oldestKey = decodeCache.keys().next().value!;
+    decodeCacheBytes -= decodeCache.get(oldestKey)!.byteLength;
+    decodeCache.delete(oldestKey);
   }
   counts.misses++;
   return features;