[Edge][CPU] Fused norms off by default, and register the switches this branch added

Two corrections and the paperwork they imply.

The fused-RMSNorm registration defaulted to *on*, which contradicts the
measurement it was committed with: those kernels are 3.6x and 4.5x faster in
isolation but measured 72.7 tok/s against 74.0 end to end, because inductor
already fuses the native norm into the residual add and an opaque call breaks
that fusion. The implementations stay registered, so the provider remains
selectable through `kernel_config.ir_op_priority` on a machine where the trade
lands differently; only the default ranking is left alone now, and the test
asserts both states rather than just the opt-in one.

The four switches this branch added (VLLM_OMNI_AOT_CACHE_SHIM,
_CPU_FUSED_NORMS, _CPU_RELEASE_MEMORY, _SPARK_GATE_REDUCTION) were not in the
reviewed environment-variable inventory, so
`test_statically_resolvable_environment_accesses_are_classified` failed. They
are classified now, the reviewed count moves 28 -> 32 with a note saying why,
and each has a row in docs/configuration/environment_variables.md carrying the
measurement that justifies its default.

`VLLM_OMNI_CPU_FAST_SAMPLER` and `VLLM_OMNI_STEP_STATS_SYNC` remain
unclassified and that test still fails on them. They arrived in 6ce8de1b, in
files this branch does not touch, so they are left to whoever owns that work
rather than documented from a guess.

Under `-m "core_model and cpu"`: 2593 passed before these fixes with 9
failures, of which two were mine. The rest are CUDA-only tests in a CPU venv
("Torch not compiled with CUDA enabled") plus test_qnn_export.py, which
another session is actively editing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/configuration/environment_variables.md

@@ -84,6 +84,10 @@ depends on the installed kernels and model path.
 | `SPEAKER_MAX_UPLOADED` | Integer; default `1000` | Speech server; read when speaker storage initializes | Environment-only setting. A non-integer logs a warning and uses `1000`; range is not otherwise validated. | Stable |
 | `VLLM_OMNI_ASYNC_OUTPUT_TIMEOUT` | Float seconds; default `600` | Diffusion engine async-output wait in `step_streaming`; resolved per call on the request path, not at import | Environment-only setting. A non-float or `<=0` value warns once and uses the default. | Experimental |
 | `VLLM_OMNI_EVENT_DRIVEN_ORCH` | `1`, `true`, `yes` or `on` enables; default `0` (off) | Orchestration loop and the serving-side final-output drain; read once when the `Orchestrator` is constructed | Environment-only setting. Values are stripped and case-normalized; any unrecognized value leaves the legacy poll loop selected. | Experimental |
+| `VLLM_OMNI_AOT_CACHE_SHIM` | `1` enables (default); `0` disables | CPU only; installed at `import vllm_omni` (`vllm_omni/patch.py`) | Environment-only setting. vLLM's CPU backend cannot load its own AOT-compiled model: `_try_load_aot_compiled_fn` calls `finalize_loading` on an artifact that is a plain function there, so the `AttributeError` is treated as a cache miss and the model is recompiled on every start. The shim attaches the missing no-op; measured warm start 49.8 s -> 14.9 s on Spark-X2.5-1.7B. Set `0` to restore stock behaviour. | Experimental |
+| `VLLM_OMNI_CPU_FUSED_NORMS` | `1` enables; default off | CPU only; read by `vllm_omni/model_executor/layers/cpu_ir_ops.py` | Environment-only setting. Ranks vLLM's own `_C::rms_norm` / `_C::fused_add_rms_norm` kernels ahead of the native path (vLLM gates them on `GPGPU_DEVICE`, so CPU never uses them). Off by default because it lost in situ: 3.6x and 4.5x faster in isolation, but 72.7 tok/s against 74.0 end to end, since inductor already fuses the native norm into the residual add. | Experimental |
+| `VLLM_OMNI_CPU_RELEASE_MEMORY` | `1` enables (default); `0` disables | CPU only; hooks `CPUWorker.load_model` and `compile_or_warm_up_model` (`vllm_omni/edge/memory.py`) | Environment-only setting. Returns freed weight-loading arenas to the OS. Loading a quantized checkpoint unpacks 4-bit codes to int32 (four bytes per weight) to repack them; the intermediates are freed but the allocator keeps them. Measured 7338 -> 3510 MB of anonymous RSS on Spark-X2.5-1.7B W4A8. | Experimental |
+| `VLLM_OMNI_SPARK_GATE_REDUCTION` | `auto` (default), `1`, `0` | Spark-X2.5 attention (`vllm_omni/model_executor/models/spark2_5/spark2_5.py`) | Environment-only setting. `auto` uses a broadcast-and-reduce for the head-wise gate on CPU and a matmul elsewhere. A 2048x8 projection cannot amortize a thread fan-out: as `aten::mm` it costs 1.155 ms of a decode step, as a reduction 0.444 ms. Override to pin either form when measuring on new hardware. | Experimental |
 | `VLLM_OMNI_CPU_INDUCTOR` | `1` enables; default off | CPU OmniPlatform (`VLLM_TARGET_DEVICE=cpu`); read when the platform reports `supports_torch_inductor` | Environment-only setting. Turns on torch.compile/inductor for the CPU AR model runner (measured variant, see `benchmarks/tts/cpu_thread_sweep.py`). | Experimental |
 | `VLLM_OMNI_HW_PROFILE` | Filesystem path to a hardware-profile JSON | `deploy_profile="auto"` hardware adaptation (`vllm_omni/edge/hardware_probe.py`); read when the profile is loaded | Environment-only override of the live probe, used for emulation and tests; an unreadable file raises. | Experimental |
 | `VLLM_OMNI_INIT_TIMELINE` | Filesystem path (JSON) | Engine init timeline (`vllm_omni/engine/init_timeline.py`); read when `AsyncOmniEngine` starts | Environment-only setting. When set, init phases from the orchestrator and every stage worker are merged and written to this path; a partial timeline is written on init timeout. | Diagnostic |