From 336fd9c49fff3e2e2d8ce751007fab52a9a6f044 Mon Sep 17 00:00:00 2001
From: austinried <4966622+austinried@users.noreply.github.com>
Date: Fri, 9 Oct 2026 07:42:05 +0000
Subject: [PATCH] build: guard local gradle runs against exhausting the box

The devshell `gradle` now serialises local builds with flock and runs
them under `nice` with capped workers, so several agents building at
once queue instead of piling up daemons and compile workers and taking
the machine down. With CI/GITHUB_ACTIONS set it execs Gradle directly,
leaving CI untouched. Also shorten the Gradle daemon idle timeout so
idle daemons are reaped sooner.
---
 AGENTS.md         |  1 +
 flake.nix         | 10 +++++++++-
 gradle.properties |  1 +
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/AGENTS.md b/AGENTS.md
index 5e3b046a..241af7bf 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -14,6 +14,7 @@ Everything comes from the Nix flake devshell; do not install toolchains by hand.
 - The default devshell provides JDK 21, Gradle 9, the Android SDK (platform 37, build-tools 37.0.0, platform-tools 37.0.1) and nushell.
 - The integration harness needs real servers, so it lives in a separate `nix develop .#integration` shell (navidrome, gonic, lms, php, Nextcloud with the Music app, sqlite). Keeping them out of the default shell avoids pulling that closure into everyday builds.
 - Build with the devshell `gradle`, not `./gradlew`. CI uses the nix Gradle pinned by `flake.lock`; the wrapper is kept only for people without Nix.
+- The devshell `gradle` is a wrapper: outside CI it takes a lock (`flock /tmp/subtracks-gradle.lock`) and runs under `nice` with capped workers, so several agents building at once queue instead of exhausting the box. With `CI`/`GITHUB_ACTIONS` set (i.e. CI) it execs Gradle directly, unchanged.
 
 ## Commands
 
diff --git a/flake.nix b/flake.nix
index 6a76b535..2a465840 100644
--- a/flake.nix
+++ b/flake.nix
@@ -40,9 +40,17 @@
           };
           androidSdk = android.androidsdk;
 
+          gradle_wrapper = pkgs.writeShellScriptBin "gradle" ''
+            if [ -n "''${CI:-}''${GITHUB_ACTIONS:-}" ]; then
+              exec ${pkgs.gradle_9}/bin/gradle "$@"
+            fi
+            exec ${pkgs.util-linux}/bin/flock /tmp/subtracks-gradle.lock \
+              ${pkgs.coreutils}/bin/nice -n 10 ${pkgs.gradle_9}/bin/gradle --max-workers=4 "$@"
+          '';
+
           basePackages = [
             pkgs.jdk21
-            pkgs.gradle_9
+            gradle_wrapper
             pkgs.git
             pkgs.curl
             pkgs.unzip
diff --git a/gradle.properties b/gradle.properties
index 4839c061..889e554e 100644
--- a/gradle.properties
+++ b/gradle.properties
@@ -3,6 +3,7 @@ org.gradle.parallel=true
 org.gradle.caching=true
 org.gradle.configuration-cache=true
 org.gradle.configuration-cache.problems=warn
+org.gradle.daemon.idletimeout=600000
 
 android.useAndroidX=true
 android.nonTransitiveRClass=true