fix(pkgbuild): honour CARGO_TARGET_DIR in install path

The act_runner exports CARGO_TARGET_DIR=/cache/target for cache
persistence, but the three Rust-app PKGBUILDs hardcoded
target/release/<bin>. Run 87 compiled 8 min then failed at
install stage. Use ${CARGO_TARGET_DIR:-target} so both CI and
local makepkg work.

DECISIONS.md

@@ -1,5 +1,11 @@
 # Decisions
 
+## 2026-04-23 – Rust PKGBUILDs honour CARGO_TARGET_DIR
+- **Who**: Dominik, ClaudeCode
+- **Why**: The act_runner container sets `CARGO_TARGET_DIR=/cache/target` (for cross-build cache persistence), but `moongreet-git`/`moonlock-git`/`moonset-git` `package()` hardcoded `target/release/<bin>`. Run 87 compiled for 8 min and then failed at `install: cannot stat 'target/release/moongreet'` because the binary actually lived in `/cache/target/release/`. Silent until today because earlier builds pre-date the env var.
+- **Tradeoffs**: None meaningful — the fallback `${CARGO_TARGET_DIR:-target}` preserves local `makepkg` builds (no env var → still reads from `./target/`).
+- **How**: Patched `install -Dm755` in all three Rust-app PKGBUILDs to use `"${CARGO_TARGET_DIR:-target}/release/<bin>"`.
+
 ## 2026-04-23 – Single-threaded, low-priority build in CI to keep the Gitea host alive
 - **Who**: Dominik, ClaudeCode
 - **Why**: The act_runner container shares CPU/RAM/I/O with the Gitea host (network-host mode, no resource limits). Parallel Rust builds OOM-kill or thrash the host: run 86 (2026-04-23, moongreet-git 0.8.3.r1) stopped mid-compile at `Compiling gio v0.22.2` with no error, and gitea HTTPS was unreachable for ~11 min. Same pattern on 2026-04-20. Runner-side resource limits would be better, but require host-side config changes; a pipeline-side fix is portable and low-risk.

moongreet-git/PKGBUILD

@@ -40,7 +40,7 @@ build() {
 
 package() {
     cd "$srcdir/greetd-moongreet"
-    install -Dm755 target/release/moongreet "$pkgdir/usr/bin/moongreet"
+    install -Dm755 "${CARGO_TARGET_DIR:-target}/release/moongreet" "$pkgdir/usr/bin/moongreet"
 
     # Greeter config
     install -Dm644 config/moongreet.toml "$pkgdir/etc/moongreet/moongreet.toml"

moonlock-git/PKGBUILD

@@ -46,7 +46,7 @@ build() {
 
 package() {
     cd "$srcdir/moonlock"
-    install -Dm755 target/release/moonlock "$pkgdir/usr/bin/moonlock"
+    install -Dm755 "${CARGO_TARGET_DIR:-target}/release/moonlock" "$pkgdir/usr/bin/moonlock"
 
     # PAM configuration
     install -Dm644 config/moonlock-pam "$pkgdir/etc/pam.d/moonlock"

moonset-git/PKGBUILD

@@ -38,7 +38,7 @@ build() {
 
 package() {
     cd "$srcdir/moonset"
-    install -Dm755 target/release/moonset "$pkgdir/usr/bin/moonset"
+    install -Dm755 "${CARGO_TARGET_DIR:-target}/release/moonset" "$pkgdir/usr/bin/moonset"
 
     # Example config
     install -Dm644 config/moonset.toml "$pkgdir/etc/moonset/moonset.toml.example"