perf(lab): compile with the Kotlin daemon, since in-process Kotlin compiles always redo the whole app

docs/lab-builds.md

@@ -52,7 +52,9 @@ tools/agent/setup
 
 It installs Claude Code, git, gh and loopback adb, plus the build toolchain: JDK 17, the Android
 SDK platform, and Google's x86-64 `aapt2` run under `qemu-user`. The first Lab build compiles the
-whole app and takes about 20 minutes on a Snapdragon 865; later ones are incremental. Setup
+whole app and takes about 8 minutes on a Snapdragon 865; later ones compile only what changed.
+That needs the Kotlin daemon: Kotlin's in-process compiles always redo the whole app. BuildConfig
+is given the installed commit, so committing a change does not change it. Setup
 does that first build ahead of time with `dd-lab-build --prepare`, which compiles the installed
 commit without making a Lab build.
 `~/.cache/dd-lab-build.json` reports the stage, the current task, progress in thousandths and the

tools/agent/dd-lab-build

@@ -96,15 +96,24 @@ if [ ! -d "$ANDROID_HOME/platforms/android-34" ]; then
   "$ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager" "platforms;android-34" "build-tools;35.0.0" >/dev/null
 fi
 
-# A full Kotlin compile of the app needs about 3 GB of heap; smaller devices get what they can spare.
+# A full Kotlin compile of the app needs about 2.5 GB of heap and Gradle about 1 GB; smaller devices get
+# what they can spare. Both daemons end with this script's process when the build is done.
 total_mb=$(awk '/^MemTotal:/ {print int($2 / 1024)}' /proc/meminfo)
-heap=$(( total_mb * 2 / 5 )); [ $heap -gt 3072 ] && heap=3072; [ $heap -lt 1536 ] && heap=1536
+heap=$(( total_mb / 2 )); [ $heap -gt 4096 ] && heap=4096; [ $heap -lt 2048 ] && heap=2048
 heap=${DD_LAB_HEAP_MB:-$heap}
+kotlin_heap=$(( heap * 2 / 3 )); gradle_heap=$(( heap - kotlin_heap ))
+
+# Only the Kotlin daemon compiles incrementally; in-process compiles always redo the whole app, and the
+# caches they leave behind make the daemon's first incremental compile fail.
+if [ "$(cat "$cache/dd-lab-build-strategy" 2>/dev/null)" != daemon ]; then
+  rm -rf app/build/kotlin/compileReleaseKotlin
+  echo daemon > "$cache/dd-lab-build-strategy"
+fi
 
 # Google publishes aapt2 for x86-64 Linux only; setup wraps it in qemu-user at ~/aapt2/aapt2.
 gradle=(./gradlew :app:processReleaseResources :app:mergeDexRelease --max-workers=2 -PskipRust=true -x buildVkBridgeServer
-  -Pandroid.aapt2FromMavenOverride=$HOME/aapt2/aapt2 -Pkotlin.compiler.execution.strategy=in-process
-  -Dorg.gradle.jvmargs=-Xmx${heap}m --console=plain)
+  -Pandroid.aapt2FromMavenOverride=$HOME/aapt2/aapt2 -Pkotlin.compiler.execution.strategy=daemon
+  -Pkotlin.daemon.jvmargs=-Xmx${kotlin_heap}m -Dorg.gradle.jvmargs=-Xmx${gradle_heap}m --console=plain)
 progress planning
 mapfile -t plan < <("${gradle[@]}" --dry-run -q 2>/dev/null | awk '/^:/ {print $1}' || true)
 total=${#plan[@]}