diff --git a/local/build-all.R b/local/build-all.R
index f8e8efd..56f1fbc 100644
--- a/local/build-all.R
+++ b/local/build-all.R
@@ -96,6 +96,10 @@ s3_cache <- readRDS("/mnt/cache/packages/s3_cache.rds")
 sprintf("S3 cache: %s files", length(s3_cache))
 
 n <- nrow(chunk)
+# Every `trim_every` packages, bound the pkgcache _metadata dir so a full-platform
+# run does not accumulate thousands of ~70 MB snapshots and fill the host disk.
+# No-op on amd64 (R_PKG_CACHE_DIR is empty / cache not persisted).
+trim_every <- 25L
 mapply(
   function(pkg, ver, sens, i) {
     cat(sprintf("[%d/%d] %s_%s (r_minor_sensitive=%s)\n", i, n, pkg, ver, sens))
@@ -120,6 +124,12 @@ mapply(
       upload = TRUE,
       store_build_metadata = TRUE
     )
+    if (i %% trim_every == 0L) {
+      removed <- trim_pkgcache_metadata()
+      if (removed > 0L) {
+        cat(sprintf("  [pkgcache trim] removed %d stale _metadata entries\n", removed))
+      }
+    }
   },
   chunk$Package,
   chunk$Version,