diff --git a/ci/build.sh b/ci/build.sh
index 4e3269b..6e6b8b7 100755
--- a/ci/build.sh
+++ b/ci/build.sh
@@ -5,8 +5,14 @@
 # from ci/Containerfile, then runs the given cargo command inside it
 # against a product repo checkout.
 #
-# Usage: ci/build.sh <product-repo-root> <cargo-command...>
-#   e.g. ci/build.sh /path/to/breadpad cargo build --release --locked
+# Usage: ci/build.sh <product-name> <product-repo-root> <cargo-command...>
+#   e.g. ci/build.sh breadpad /path/to/breadpad cargo build --release --locked
+#
+# <product-name> is used verbatim as the image tag and cache-volume name —
+# it must be passed explicitly rather than derived from <product-repo-root>'s
+# basename, because every product's CI checks out into a directory literally
+# named `src`, which would otherwise collide across every product sharing
+# this runner (same image tag, same cargo-target cache volume).
 #
 # If <product-repo-root>/ci/deps.txt exists (one pacman package per line,
 # '#' comments and blank lines ignored), those packages are installed on
@@ -17,16 +23,16 @@
 # per-product. Both persist in named docker volumes across runs.
 set -euo pipefail
 
-if [ $# -lt 2 ]; then
-    echo "usage: build.sh <product-repo-root> <cargo-command...>" >&2
+if [ $# -lt 3 ]; then
+    echo "usage: build.sh <product-name> <product-repo-root> <cargo-command...>" >&2
     exit 1
 fi
 
-REPO_ROOT="$(cd "$1" && pwd)"
-shift
+PRODUCT="$1"
+REPO_ROOT="$(cd "$2" && pwd)"
+shift 2
 
 CI_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-PRODUCT="$(basename "$REPO_ROOT")"
 
 EXTRA_PKGS=""
 if [ -f "${REPO_ROOT}/ci/deps.txt" ]; then