Cap ninja parallelism to stop flutter run from OOMing

flutter_tools shells out to bare `ninja -C <dir> install` with no -j
flag, so ninja defaults to nproc+2 parallel compile/link jobs. On this
6-core/7.6GiB box that's enough concurrent clang jobs (sqlite3's
single-TU amalgamation is the worst offender) to trip systemd-oomd
well before swap fills up.

Add tools/ninja-jcap, a PATH-shadowing ninja shim that caps jobs via
NINJA_JOBS (default 2), and have the Taskfile prepend it inline in the
run command. Task's `env:` block can't override PATH itself (the OS
env wins), so the shim has to go on PATH via the shell command line.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Taskfile.yml

@@ -0,0 +1,20 @@
+version: '3'
+
+vars:
+  FLUTTER: /var/home/ironmagma/Code/.flutter-sdk/bin/flutter
+
+tasks:
+  default:
+    desc: Launch Layer Wizard
+    env:
+      # GTK/glib/etc. come from Homebrew (brew install gtk+3), not rpm-ostree,
+      # since they're only needed to build this one app, not the OS image.
+      PKG_CONFIG_PATH: /home/linuxbrew/.linuxbrew/lib/pkgconfig:/home/linuxbrew/.linuxbrew/share/pkgconfig:/home/linuxbrew/.linuxbrew/opt/xorgproto/share/pkgconfig
+    cmds:
+      # flutter_tools shells out to bare `ninja -C <dir> install` with no -j
+      # flag, so ninja defaults to nproc+2 parallel compile/link jobs. That's
+      # enough to trip systemd-oomd on this machine (6 cores, 7.6GiB RAM).
+      # (Task's `env:` block can't override PATH itself -- the OS env wins --
+      # so the shim has to be prepended inline here instead.) See
+      # tools/ninja-jcap for the shim that caps it.
+      - 'PATH="{{.ROOT_DIR}}/tools/ninja-jcap:$PATH" {{.FLUTTER}} run -d linux'

tools/ninja-jcap/ninja

@@ -0,0 +1,31 @@
+#!/usr/bin/env bash
+# Shim that caps ninja's parallelism before handing off to the real binary.
+#
+# `flutter run`/`flutter build` for the linux target invoke bare `ninja -C
+# <dir> install` with no -j flag (flutter_tools gives no way to pass one), so
+# ninja defaults to nproc+2 concurrent compile/link jobs. On this machine
+# (6 cores, 7.6GiB RAM) that's enough parallel clang jobs -- especially
+# linking the sqlite3 amalgamation with debug info -- to trip systemd-oomd
+# well before swap fills up. Capping jobs here keeps `task` usable without
+# patching flutter_tools.
+#
+# Override with NINJA_JOBS=N if this box has more headroom.
+set -euo pipefail
+
+self_dir=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+
+real_ninja=""
+IFS=':' read -ra path_dirs <<< "$PATH"
+for dir in "${path_dirs[@]}"; do
+  if [[ "$dir" != "$self_dir" && -x "$dir/ninja" ]]; then
+    real_ninja="$dir/ninja"
+    break
+  fi
+done
+
+if [[ -z "$real_ninja" ]]; then
+  echo "ninja-jcap: couldn't find a real ninja later in PATH" >&2
+  exit 1
+fi
+
+exec "$real_ninja" -j "${NINJA_JOBS:-2}" "$@"