Add GPU_FOREIGN_UTIL_PCT: game detection via per-process GPU 3D-engine usage

Reads the same PDH counters as Task Manager (\GPU Engine(*)\Utilization
Percentage, locale-independent via PdhAddEnglishCounterW), which cover
graphics work under WDDM — games are caught without an exe list and the
offender is named. Windows-only; a missing or failing counter disables
the path with one log line. dwm (the desktop compositor) joins the
default ignore list.

SPEC.md

@@ -55,9 +55,9 @@ consumer gets no listener, no startup probe, and no lock participation:
 - **Only `COMFY_URL`**: image jobs are tracked and ComfyUI's VRAM is freed
   afterwards, but the Ollama unload and warm-reload steps are skipped.
 - **Game detection** is a third, optional consumer without a URL: enabled by
-  `GAME_PROCS` and/or `GPU_FOREIGN_VRAM_MB` it watches for foreign processes
-  holding the GPU (see below) and plugs into the same lock the same way —
-  excluded when both knobs are unset.
+  `GAME_PROCS`, `GPU_FOREIGN_VRAM_MB` and/or `GPU_FOREIGN_UTIL_PCT` it
+  watches for foreign processes holding the GPU (see below) and plugs into
+  the same lock the same way — excluded when all knobs are unset.
 
 ### Lock semantics
 
@@ -171,20 +171,26 @@ files are flagged in the startup log.
 ## Game detection (foreign GPU holders)
 
 Games and other foreign GPU users sit outside the URL-based consumer model —
-nothing proxies through gpu-turnstile for them. Two independent detection
-paths, polled every `GAME_POLL_INTERVAL` (default 15 s); either one being
+nothing proxies through gpu-turnstile for them. Three independent detection
+paths, polled every `GAME_POLL_INTERVAL` (default 15 s); any one being
 configured enables the feature:
 
 - **Process watch list** (`GAME_PROCS`, comma-separated, case-insensitive,
   `.exe` optional): while any listed process runs, the GPU counts as held.
-  This is the reliable path on Windows.
+- **Foreign 3D-engine utilization** (`GPU_FOREIGN_UTIL_PCT`, Windows only):
+  per-process GPU engine counters from PDH — the same data Task Manager
+  shows — cover graphics work under WDDM, so any process not in
+  `GPU_IGNORE_PROCS` using more than the threshold percent of the 3D engine
+  counts as a foreign holder, with no exe list needed. Values are summed per
+  process across engines; a missing/failing PDH counter disables the path
+  (logged once).
 - **Foreign VRAM threshold** (`GPU_FOREIGN_VRAM_MB`): `nvidia-smi
   --query-compute-apps` lists per-process GPU memory; any process not in
-  `GPU_IGNORE_PROCS` (default: Ollama and python — ComfyUI runs under python)
-  holding more than the threshold counts as a foreign holder. Needs
-  nvidia-smi on the PATH (absent: logged once, path disabled) and works best
-  on Linux — under Windows' WDDM driver, graphics-only games may not appear
-  in the per-process list.
+  `GPU_IGNORE_PROCS` (default: Ollama and python — ComfyUI runs under python
+  — plus dwm, the desktop compositor) holding more than the threshold counts
+  as a foreign holder. Needs nvidia-smi on the PATH (absent: logged once,
+  path disabled) and works best on Linux — under Windows' WDDM driver,
+  graphics-only games may not appear in the per-process list.
 
 While a holder is detected, gpu-turnstile:
 
@@ -230,7 +236,8 @@ override file values. A missing file is fine; a malformed one is fatal.
 | `COMFY_START_TIMEOUT` | `2m` | how long a request waits for the managed ComfyUI to come up |
 | `GAME_PROCS` | _(empty = disabled)_ | comma-separated process names (case-insensitive, `.exe` optional); while any runs, the GPU counts as held by it: requests wait, Ollama unloads, the managed ComfyUI stops |
 | `GPU_FOREIGN_VRAM_MB` | `0` (disabled) | also treat the GPU as held when a process not in `GPU_IGNORE_PROCS` uses more VRAM than this; needs nvidia-smi |
-| `GPU_IGNORE_PROCS` | `ollama,ollama app,ollama_llama_server,python,pythonw` | process names never counted as foreign GPU users |
+| `GPU_FOREIGN_UTIL_PCT` | `0` (disabled) | also treat the GPU as held when a process not in `GPU_IGNORE_PROCS` uses more than this percent of the GPU 3D engine (Windows PDH counters, as shown by Task Manager; catches games without an exe list) |
+| `GPU_IGNORE_PROCS` | `ollama,ollama app,ollama_llama_server,python,pythonw,dwm` | process names never counted as foreign GPU users |
 | `GAME_POLL_INTERVAL` | `15s` | how often game/VRAM detection runs (nvidia-smi polls keep the GPU awake; don't go below ~10s) |
 | `LOGLEVEL` | `warn` | `info` logs every request (colored arrows in text mode), `debug` adds lock transitions. `LOG_LEVEL` is accepted as an alias |
 | `LOG_FORMAT` | `text` | `json` for structured JSON logs |