fix(dev): the smoke target died silently on a genuinely dead app

Two harness bugs and the finding that exposed them.

**`pidof` exits 1 when it finds nothing**, and under `set -e` a failing
command substitution killed the script before it could print anything
-- rc=1, no output. That was invisible for as long as the app
crash-*looped*, because there is always some pid in that state. It
appeared the moment the app died for good and ActivityManager stopped
respawning it, which is precisely the run you most want output from.

**And an install failure said nothing useful.** Both ways it fails are
about identity rather than the build: INSTALL_FAILED_VERSION_DOWNGRADE
when a bare `make android` (versionCode 1) meets something a versioned
build left behind, and a signature mismatch when a debug-signed local
build meets a release-signed one. Both were hit in one session, and
both are fixed by uninstalling. The target says so now instead of
leaving someone to read the constant name.

The finding: with the startup bug fixed the app reaches the database
and takes SIGSYS on the x86_64 emulator, because modernc.org/libc's
Xlstat64 issues a raw lstat syscall on linux/amd64 and Android's
seccomp filter forbids it -- bionic never issues it. arm64 has no lstat
syscall at all, so ccgo_linux_arm64.go routes Xlstat through fstatat
and is structurally unaffected; Go's own syscall package already used
fstatat on both.

So the default emulator cannot verify this app, and the skill says so
rather than letting the next session read a tombstone as a regression.

scripts/android-emulator.sh

@@ -162,7 +162,42 @@ cmd_install() {
 	need_sdk
 	[ -f bin/yellowjacket.apk ] || die "no bin/yellowjacket.apk — run 'make android' first"
 	"$ADB" get-state >/dev/null 2>&1 || die "no device — run 'make android-emulator' first"
-	"$ADB" install -r bin/yellowjacket.apk
+
+	# The two ways this fails are both about identity rather than the
+	# build, and neither error says what to do about it.
+	#
+	# A *downgrade* is the versionCode rule working as designed: a bare
+	# `make android` produces versionCode 1, so it will not install over
+	# anything a versioned build left behind.  A *signature* mismatch is
+	# the rule this whole pipeline exists for — a debug-signed local
+	# build cannot replace a release-signed one.
+	#
+	# Both are fixed by uninstalling, and on a throwaway emulator that
+	# costs nothing, so say so rather than making someone read the
+	# constant name.
+	out=$("$ADB" install -r bin/yellowjacket.apk 2>&1) || {
+		printf '%s\n' "$out"
+		case "$out" in
+		*INSTALL_FAILED_VERSION_DOWNGRADE*)
+			echo
+			echo "The installed copy has a higher versionCode than this build."
+			echo "A bare 'make android' builds versionCode 1; a versioned one"
+			echo "builds e.g. 10301.  Either uninstall:"
+			echo "    $ADB uninstall $PKG"
+			echo "or build with a version:"
+			echo "    YJ_VERSION=1.3.1 YJ_VERSION_CODE=10301 make android"
+			;;
+		*INSTALL_FAILED_UPDATE_INCOMPATIBLE* | *signatures do not match*)
+			echo
+			echo "The installed copy was signed with a different key.  Android"
+			echo "never allows that as an update — which is exactly why CI"
+			echo "refuses to publish a debug-signed APK.  Uninstall:"
+			echo "    $ADB uninstall $PKG"
+			;;
+		esac
+		return 1
+	}
+	printf '%s\n' "$out"
 }
 
 cmd_launch() {
@@ -190,11 +225,17 @@ cmd_smoke() {
 
 	cmd_launch
 	sleep 3
-	local first
-	first=$("$ADB" shell pidof "$PKG" 2>/dev/null | tr -d '\r' | awk '{print $1}')
+	# **`|| true` is load-bearing.** `pidof` exits 1 when it finds
+	# nothing, and under `set -e` a failing command substitution kills
+	# the script -- silently, before it can print why. That is invisible
+	# for as long as the app crash-*loops*, because there is always some
+	# pid; it appears the moment the app dies for good and ActivityManager
+	# stops respawning it, which is exactly the run you most want output
+	# from.
+	local first second
+	first=$("$ADB" shell pidof "$PKG" 2>/dev/null | tr -d '\r' | awk '{print $1}' || true)
 	sleep "$wait_s"
-	local second
-	second=$("$ADB" shell pidof "$PKG" 2>/dev/null | tr -d '\r' | awk '{print $1}')
+	second=$("$ADB" shell pidof "$PKG" 2>/dev/null | tr -d '\r' | awk '{print $1}' || true)
 
 	if [ -n "$first" ] && [ "$first" = "$second" ]; then
 		echo "PASS: $PKG alive as pid $first after ${wait_s}s"