Phase 3: asus-zephyrus-g14 and memory-pressure, with Go tools and long-running code

The laptop model's hardware module and a memory-pressure module for any
machine (hq research 027/03, 026/05, to-be 42 phase 3). The predecessor's
polling auto-profile and mem-guard user scripts become each module's own
Go code launched by the node runtime (ADR 0198): a profile switcher woken
by the kernel's power-supply uevents, and a guard that warns on RAM, swap
or PSI before systemd-oomd acts, on the desktop over the account's bus and
always as an event. supergfxctl and triggerhappy are kept as found
(research 027 Q1).

modules/memory-pressure/module.json

@@ -0,0 +1,121 @@
+{
+  "module": "memory-pressure",
+  "version": "1",
+  "capabilities": [
+    "package-manager",
+    "service-manager"
+  ],
+  "emits": [
+    "pressure.high",
+    "pressure.cleared"
+  ],
+  "tools": [
+    "memory_status",
+    "memory_top",
+    "memory_oom_history",
+    "memory_zram",
+    "memory_oomd",
+    "memory_guard"
+  ],
+  "resources": [
+    {
+      "id": "zram-generator",
+      "type": "package",
+      "package": "zram-generator"
+    },
+    {
+      "id": "zram",
+      "type": "file",
+      "path": "/etc/systemd/zram-generator.conf",
+      "mode": "0644",
+      "content": "# Managed by the mesh (module memory-pressure). Replaced on every push; edit the catalogue instead.\n#\n# Compressed swap in RAM: fast, at a higher priority than any swap on disk, so it takes the everyday\n# pressure before anything spills to a disk. Half the RAM, at most 16 GiB, compressed with zstd.\n# The swap on disk, its size and whether one exists at all are the machine's, not this module's.\n#\n# Read by the generator at boot: a change applies at the next boot.\n[zram0]\nzram-size = min(ram / 2, 16384)\ncompression-algorithm = zstd\nswap-priority = 100\n"
+    },
+    {
+      "id": "sysctl-drop-ins",
+      "type": "directory",
+      "path": "/etc/sysctl.d",
+      "mode": "0755"
+    },
+    {
+      "id": "swap-tunables",
+      "type": "file",
+      "path": "/etc/sysctl.d/90-memory-pressure.conf",
+      "mode": "0644",
+      "content": "# Managed by the mesh (module memory-pressure). Replaced on every push; edit the catalogue instead.\n#\n# Swap-in reads one page, not eight: read-ahead exists to amortise a disk's seek, and compressed swap in\n# RAM has none — the speculation only costs decompression and memory.\nvm.page-cluster = 0\n#\n# vm.swappiness is deliberately left alone. The usual zram advice (150-180) holds only while the\n# compressed swap has room; once it is full, a higher swappiness moves pages to the disk swap, the thing\n# being avoided. Raise it only together with zram-size.\n"
+    },
+    {
+      "id": "sysctl",
+      "type": "service",
+      "unit": "systemd-sysctl.service",
+      "restart-on": [
+        "swap-tunables"
+      ]
+    },
+    {
+      "id": "oomd-drop-ins",
+      "type": "directory",
+      "path": "/etc/systemd/oomd.conf.d",
+      "mode": "0755"
+    },
+    {
+      "id": "oomd-limits",
+      "type": "file",
+      "path": "/etc/systemd/oomd.conf.d/memory-pressure.conf",
+      "mode": "0644",
+      "content": "# Managed by the mesh (module memory-pressure). Replaced on every push; edit the catalogue instead.\n#\n# systemd-oomd kills the worst unit before the kernel's OOM killer freezes the machine: when swap is\n# 90 % used, or when a watched unit stalls on memory for 20 s above its limit.\n[OOM]\nSwapUsedLimit=90%\nDefaultMemoryPressureLimit=60%\nDefaultMemoryPressureDurationSec=20s\n"
+    },
+    {
+      "id": "root-slice-drop-ins",
+      "type": "directory",
+      "path": "/etc/systemd/system/-.slice.d",
+      "mode": "0755"
+    },
+    {
+      "id": "root-slice",
+      "type": "file",
+      "path": "/etc/systemd/system/-.slice.d/10-oomd.conf",
+      "mode": "0644",
+      "content": "# Managed by the mesh (module memory-pressure). Replaced on every push; edit the catalogue instead.\n#\n# systemd-oomd may act on swap exhaustion across the whole machine.\n[Slice]\nManagedOOMSwap=kill\n"
+    },
+    {
+      "id": "user-manager-drop-ins",
+      "type": "directory",
+      "path": "/etc/systemd/system/user@.service.d",
+      "mode": "0755"
+    },
+    {
+      "id": "user-manager",
+      "type": "file",
+      "path": "/etc/systemd/system/user@.service.d/10-oomd.conf",
+      "mode": "0644",
+      "content": "# Managed by the mesh (module memory-pressure). Replaced on every push; edit the catalogue instead.\n#\n# systemd-oomd may kill the worst unit in a person's service manager when its memory pressure stays\n# above 80 % — instead of the kernel freezing the machine.\n[Service]\nManagedOOMMemoryPressure=kill\nManagedOOMMemoryPressureLimit=80%\n"
+    },
+    {
+      "id": "oomd",
+      "type": "service",
+      "unit": "systemd-oomd.service",
+      "state": "running",
+      "boot": "enabled",
+      "restart-on": [
+        "oomd-limits",
+        "root-slice",
+        "user-manager"
+      ]
+    }
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools-go",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/memory-pressure",
+        "binary": "memory-pressure",
+        "loads": [
+          "memory-pressure"
+        ]
+      }
+    ]
+  }
+}