Say that the default sweep is red on purpose, and narrow two claims

R16 / #25 -- the branch put API 37 into the default APIS list, where it is permanently two
failures short of green, so a bare `run-e2e.sh` exits 1 by design and nothing said so.
Somebody running it from habit, a wrapper or a hook gets a red exit forever and either
stops reading exit codes or debugs a normal state.

Documented rather than suppressed. The script's own comment already argued that an
expected-red level belongs in the exit code -- reversing that is the branch owner's call,
not a correction -- and the review's alternative needs an exact-set comparison of the
failing test names before it can subtract 37's contribution, which is a new mechanism that
cannot be validated without a device. So:

- the header now states the exit code (0 all green / 1 any level red / 2 refused to
  start), says a bare run is 1 by design and why, and gives `run-e2e.sh 33 34 35 36` as
  the sweep that can be green;
- a red sweep prints one note after the summary saying the same thing, because the exit
  code is read in the terminal and not in the docs -- but ONLY when 37.x is the only level
  that went red. `overall` is set by any red level, so a note keyed on "37 was in the
  list" would have called a genuine API 34 failure "by design", which is the defect this
  is meant to prevent, one layer up. mark_red records which level it was, where the loop
  already knows;
- docs/local-emulator.md says it where the default is documented.

R27 / #36 -- 792286a appended the caveat that the harness path reproduces a rate collapse
rather than a clean zero, but left "that is the confirmation that region sampling is the
sole trigger" standing three lines above it, which the caveat contradicts. Now "the
strongest evidence that region sampling is the dominant trigger", with the residue named:
no measurement here separates a second caller of the readback path from a disable that did
not fully take, and the file says so rather than picking one.

R28 / #37 -- "the capability is negotiated regardless of renderer" leaned on the string
search, which shows only that `ANDROID_EMU_read_color_buffer_dma` is implemented in one
shared component, not that it is negotiated on every path. The aborts are the actual
evidence -- the assertion that fires is `!hasReadColorBufferDma` and it fires under ANGLE
too -- and they suffice alone; the string search is demoted to a supporting note. Worth
getting right because the doc says the upstream report should lead with this model.

Two follow-ons that belong with R17 / #26 and land here rather than in their own commit:
bash runs a trap only between commands, so the handler starts when the foreground command
returns -- immediate under Ctrl-C, which reaches that command too, but not under a `kill
-INT` aimed at the script alone; that is now written next to the handler. And
delete_created_avds no longer discards avdmanager's status: an emulator that was SIGKILLed
did not get to remove its own lock files, avdmanager can refuse over them, and silence
there would leak exactly what the trap exists to clean up.

`bash -n` clean; the stub smoke harness (real script, fake SDK binaries, boot-failure path,
no Gradle and no emulator) now also checks that a 37-only red prints the note after the
summary, that a red API 34 alongside it suppresses the note, that a 34-only sweep says
nothing, and that a refused AVD deletion is reported. shellcheck is not installed here.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tools/local-emulator/run-e2e.sh

@@ -12,6 +12,15 @@
 #   BOOT_TIMEOUT=300       seconds to wait for sys.boot_completed
 #   KEEP_AVD=1             do not delete an AVD this script created
 #
+# EXIT CODE: 0 only if every level was green; 1 if any level failed, wedged or could not be
+# set up; 2 if it refused to start at all. **A bare `run-e2e.sh` therefore exits 1 by design.**
+# API 37 is in the default list on purpose -- leaving it out is what left the level unlooked-at
+# for as long as it was -- and it is permanently two failures short of green, on the emulator's
+# own c2.goldfish.h264.decoder rather than on anything this app does. The summary names the two,
+# so a third is visibly new, and the last line printed says the same thing. Anything that reads a
+# non-zero exit as breakage should name the levels it wants: `run-e2e.sh 33 34 35 36` is the
+# sweep that can be green. docs/api-37-emulator-crash.md has the measurements.
+#
 # WHY THIS EXISTS, AND WHAT IT DELIBERATELY DOES NOT DO
 #
 # It is a *launcher*, not a second test harness. The diagnostics -- the FAILED-vs-WEDGED
@@ -415,7 +424,10 @@ delete_created_avds() {
   local avd
   [ "${KEEP_AVD:-0}" = "1" ] && return 0
   for avd in ${CREATED_AVDS[@]+"${CREATED_AVDS[@]}"}; do
-    avdmanager delete avd -n "$avd" > /dev/null 2>&1
+    # A SIGKILLed emulator does not get to remove its own lock files, and avdmanager can
+    # refuse over them. Staying silent there would leak the very thing this exists to clean.
+    avdmanager delete avd -n "$avd" > /dev/null 2>&1 \
+      || echo "  WARNING: could not delete AVD $avd -- 'avdmanager delete avd -n $avd' by hand"
   done
   CREATED_AVDS=()
 }
@@ -440,6 +452,10 @@ cleanup() {
 # 6 s, not 30: Ctrl-C has already reached the emulator through the foreground process group,
 # so this is only waiting for it to finish writing, and `kill -9` follows regardless. The
 # EXIT trap is disarmed before exiting so the status below is the one that survives.
+#
+# bash runs a trap only between commands, so this starts when whatever was in the foreground
+# returns -- which for Ctrl-C is immediately, because the same interrupt reached that command
+# too. `kill -INT` aimed at this script alone waits for the foreground command to finish.
 on_signal() {
   echo
   echo "interrupted (SIG$1) -- stopping the emulator and removing the AVDs this run created"
@@ -492,6 +508,16 @@ PY
 SUMMARY=()
 overall=0
 
+# Whether the red exit is the expected one depends on which level produced it, and only the
+# loop knows that -- so it is recorded where `overall` is set rather than guessed from the
+# summary afterwards. A note at the end claiming a genuine API 34 failure was "by design"
+# would be the same defect it is there to prevent, one layer up.
+NON37_RED=0
+mark_red() {
+  overall=1
+  case "$1" in 37 | 37.*) ;; *) NON37_RED=1 ;; esac
+}
+
 for api in "${APIS[@]}"; do
   avd="$(avd_for_api "$api")"
   gpu="$(gpu_for_api "$api")"
@@ -503,7 +529,7 @@ for api in "${APIS[@]}"; do
 
   if ! ensure_avd "$api" "$avd"; then
     SUMMARY+=("API $api: AVD SETUP FAILED")
-    overall=1
+    mark_red "$api"
     continue
   fi
 
@@ -511,7 +537,7 @@ for api in "${APIS[@]}"; do
     host_forensics "$started"
     guest_forensics "$api"
     SUMMARY+=("API $api: BOOT FAILED")
-    overall=1
+    mark_red "$api"
     stop_emulator
     continue
   fi
@@ -545,7 +571,7 @@ for api in "${APIS[@]}"; do
   esac
   if [ "$rc" -ne 0 ]; then
     line="$line  [gradle exit $rc]"
-    overall=1
+    mark_red "$api"
     host_forensics "$started"
   fi
   SUMMARY+=("$line")
@@ -558,4 +584,16 @@ echo
 echo "===================== LOCAL E2E SUMMARY ======================"
 printf '%s\n' ${SUMMARY[@]+"${SUMMARY[@]}"}
 echo "=============================================================="
+
+# An unexplained red exit trains people to stop reading exit codes, and this one is expected
+# whenever API 37 is in the sweep -- which the default list makes the common case. Said here
+# rather than only in the docs, because this is where it is actually read. Only when 37.x is
+# the ONLY thing that went red: a note calling a real failure elsewhere "by design" would be
+# worse than no note at all.
+if [ "$overall" -ne 0 ] && [ "$NON37_RED" -eq 0 ]; then
+  echo "note: the only level that went red is API 37, which exits non-zero by design -- it is"
+  echo "      permanently 2 failures short of green. Confirm its row above shows exactly those"
+  echo "      two and nothing else; docs/api-37-emulator-crash.md says why they are the image."
+fi
+
 exit "$overall"