GPU memory harness

Measures how much GPU memory the render-wasm workspace uses during a long edit session, in Chromium, Firefox and WebKit, and compares builds.

Not part of CI. Needs the compiled frontend and wasm bundle that scripts/e2e-server.js serves, and a display: the projects run headed, since headless Chromium falls back to SwiftShader.

Run

From frontend/:

# one engine, labelled run
PERF_LABEL=develop npx playwright test --project gpu-memory-chromium

# after rebuilding with a change
PERF_LABEL=cache-limit npx playwright test --project gpu-memory-chromium

# compare and write playwright/perf/report.html
node playwright/perf/gpu-memory/report.mjs

Projects: gpu-memory-chromium, gpu-memory-firefox, gpu-memory-webkit.

Variable	Default	Meaning
`PERF_LABEL`	`git describe --dirty`	Name of the build under test; results go to `results/<label>/`
`PERF_FIXTURE`	`render-wasm/get-file-shadows.json`	`get-file` fixture under `playwright/data/`; served over local HTTP, so size is no limit
`PERF_REPEATS`	`3`	Runs per engine; repeat 0 is dropped as warm-up
`PERF_ITERATIONS`	`12`	Steps per phase
`PERF_DPR`	`2`	Device pixel ratio
`PERF_EDIT_TARGET`	select all	`x,y` in CSS px: the edit phase selects the element there instead of everything
`PERF_EDIT_SHAPE`	off	Shape id to select for the edit phase; wins over `PERF_EDIT_TARGET` and doesn't depend on the view
`PERF_SKIA_CACHE_MB`	build default	Skia resource cache budget, set after the first render (needs `set_resource_cache_limit_mb` in the wasm build)
`PERF_PURGE_PROBE`	off	`1` calls `free_gpu_resources` at the end and samples again
`PERF_TIMEOUT_MIN`	`15`	Time limit per run; heavy fixtures in Firefox need more
`PERF_TRACE_SIZE`	off	`WxH`: record the call stacks of allocations of that size (in each sample's `web.traces`)
`PERF_PROC_MATCH`	`ms-playwright`	Substring of the browser binary path used to find its processes

Report flags: --baseline <label> (default develop, else the oldest label), --out <file>, --keep-warmup, --json.

What a run does

Loads the fixture, then runs these phases, sampling after the renderer goes quiet: load, resize (cycles four page sizes through CSS, so every engine takes the same path), zoom, pan, edit (select all, nudge back and forth), idle, and optionally purge.

What is measured

WebGL (gpu-memory/webgl-tracker.js, every engine): bytes WebGL was asked to store in textures, renderbuffers and buffers, and a count of every storage allocation. Drivers add their own copies on top.
OS (gpu-memory/os-sampler.js, Linux only): RSS of the processes that hold a GPU device open, DRM memory from /proc/<pid>/fdinfo, dma-bufs shared by the browser, and nvidia-smi when present.

A difference counts only when medians differ by 5% or more and the run ranges don't overlap. Anything else is reported as noise.