diff --git a/lib/project-avd.sh b/lib/project-avd.sh
index ed53c4a..e428738 100644
--- a/lib/project-avd.sh
+++ b/lib/project-avd.sh
@@ -38,9 +38,24 @@ running_avds() {
 #
 # Cached, because asking costs one console round trip per attached device and
 # this runs on every single adb call -- which includes a `tap` inside a loop.
-# The cache is checked against `adb devices` first, so an emulator that has
-# gone away cannot leave a stale serial behind; that check is one round trip
-# whatever the answer.
+#
+# The cache is validated by asking the cached serial its AVD name, not merely
+# by checking that the serial is still attached. Those are different questions
+# once ports get recycled, and the cheap one says yes about the wrong device:
+# emulator serials are ports, so when ai-app-2 exits and ai-app starts, ai-app
+# takes 5554 and ai-app-2's stale cache entry stays "valid" for ever. Measured
+# on 2026-09-04, with both ai-app.serial and ai-app-2.serial holding
+# emulator-5554: every adb, ui-trace and emu call from ~/repos/ai-app-2
+# resolved to the other checkout's emulator, and `emu up` refused to start the
+# right AVD because it believed it was already running. That is precisely the
+# fan-out this whole tool exists to prevent, and it is silent.
+#
+# The name check is one round trip on a cache hit, against the one device the
+# cache names -- not the per-device sweep the cache exists to avoid. It lives
+# here rather than in any caller because `adb`, `ui-trace` and both of `emu`'s
+# uses (resolving a serial, and deciding whether to start) all come through
+# this function, and a check in only one of them is the same bug with a
+# smaller blast radius.
 avd_serial() {
     _adb=$1
     _avd=$2
@@ -48,11 +63,12 @@ avd_serial() {
     _cache="$_dir/$_avd.serial"
     if [ -r "$_cache" ]; then
         _cached=$(cat "$_cache")
-        if "$_adb" devices 2>/dev/null | awk '$2 == "device" {print $1}' |
-            grep -qx "$_cached"; then
+        _name=$("$_adb" -s "$_cached" emu avd name 2>/dev/null | head -n1 | tr -d '\r')
+        if [ "$_name" = "$_avd" ]; then
             echo "$_cached"
             return 0
         fi
+        rm -f "$_cache"
     fi
     _found=$(running_avds "$_adb" | awk -F'\t' -v want="$_avd" '$2 == want {print $1; exit}')
     [ -z "$_found" ] && return 1