Detach emulators from launching shell

README.md

@@ -131,6 +131,12 @@ starts on software rendering as it always did. None of this is essential.
 would leave the machine short, printing what is attached, what is large, and
 what usually frees enough. `EMU_FORCE=1` overrides it.
 
+The emulator is launched in its own session with stdin closed, so it outlives
+both an interactive terminal and an isolated command runner. A bare background
+job appeared to work from long-lived agent shells but was shut down as soon as
+a one-command execution session ended; the emulator's own log showed a clean
+shutdown after boot rather than a crash.
+
 The reason is a real incident rather than tidiness. On 2026-08-30 an emulator
 was started on this box with 2.8 GB available; the OOM killer ran, and what
 it took was not the emulator that had just started — it walked the user slice

bin/emu

@@ -193,6 +193,20 @@ headless_display() {
     cat "$run/display"
 }
 
+# Starts the emulator outside the caller's terminal session.
+#
+# A plain background job survives an ordinary interactive shell here, which hid this until `emu up`
+# was run through an isolated command runner: the emulator reached boot, `emu up` returned success,
+# and the runner then closed its session and asked every job still attached to it to shut down. The
+# emulator complied cleanly, so its log ended at "Boot completed" and looked like a device crash.
+# `setsid` is the process-lifetime boundary; `nohup`, a closed stdin and disown cover the shell's
+# own three ways of retaining or signalling the job. Keep every rendering branch on this path.
+start_emulator() {
+    setsid nohup "$@" </dev/null >"$log" 2>&1 &
+    pid=$!
+    disown -h "$pid"
+}
+
 cmd_up() {
     if serial=$(avd_serial "$adb" "$avd"); then
         echo "emu: '$avd' is already running ($serial)" >&2
@@ -245,21 +259,20 @@ cmd_up() {
     # Vulkan that gfxstream cannot pair with Venus here.
     if [ "${EMU_GPU:-}" != software ] && { [ -n "${DISPLAY:-}" ] || [ -n "${WAYLAND_DISPLAY:-}" ]; }; then
         echo "emu: starting '$avd' with GPU acceleration" >&2
-        "$sdk/emulator/emulator" -avd "$avd" -gpu host -no-audio >"$log" 2>&1 &
+        start_emulator "$sdk/emulator/emulator" -avd "$avd" -gpu host -no-audio
     elif [ "${EMU_GPU:-}" != software ] && display=$(headless_display); then
         echo "emu: no display -- starting '$avd' headless on the GPU ($display)" >&2
-        DISPLAY="$display" "$sdk/emulator/emulator" -avd "$avd" \
+        start_emulator env DISPLAY="$display" "$sdk/emulator/emulator" -avd "$avd" \
-            -gpu host $GPU_HOST_FEATURES -no-audio -no-window >"$log" 2>&1 &
+            -gpu host $GPU_HOST_FEATURES -no-audio -no-window
     else
         if [ "${EMU_GPU:-}" = software ]; then
             echo "emu: EMU_GPU=software -- starting '$avd' on the CPU, off the host GPU" >&2
         else
             echo "emu: no display and no compositor -- starting '$avd' on software rendering" >&2
         fi
-        "$sdk/emulator/emulator" -avd "$avd" -gpu swiftshader_indirect -no-audio -no-window \
+        start_emulator "$sdk/emulator/emulator" -avd "$avd" -gpu swiftshader_indirect \
-            >"$log" 2>&1 &
+            -no-audio -no-window
     fi
-    pid=$!
 
     for _ in $(seq 150); do
         if ! kill -0 "$pid" 2>/dev/null; then