Part of #158. **Blocks every other perf issue** — no optimization lands before there is a number to move. ### Problem We cannot currently measure the thing we are being asked to fix. - `ProfilerPanel.tickRecording` sets `engine.Profiler.enabled = active and g_record` — **profiling only happens during Play**. The ~20 fps Scene-viewport number in #158 cannot be profiled at all. - Otherwise `Profiler.enabled` defaults to `builtin.mode == .Debug`, so a compiled release build can't be profiled either. - `Profiler.Counters` are frame-global. With draws coming from the prepass, shadow, main, transparent and probe-bake passes, a single `draw_calls` number can't be attributed to any of them. - Real GPU timing is an opt-in fence stall covering **2 of 8 passes** (`gpu_timing.zig` wraps shadow and cull only). - Nothing counts indirect commands issued, so the ADR-0013 zero-instance overhead is invisible. - **There is no headless way to produce a trace.** A backgrounded, unfocused Studio never pumps frames — `profiler.capture` over the debug protocol returns an empty thread list, and synthetic input is never applied. Only `TURIAN_CAPTURE_AFTER_MS` forces real frames, because `Main.zig:612` caps `waitEventTimeout` at 16 ms while a capture is pending. That last point is why #147's acceptance criterion was never met: getting numbers requires a human at a focused window. ### Scope **a. Headless benchmark mode.** ``` turian-studio --benchmark <project> [--scene <path>] [--frames N] [--camera <name>] [--warmup N] [--features <spec>] ``` Reuses the `capture_pending` mechanism in `Main.zig:605-613` to keep an unfocused window pumping, drives N frames from a fixed or scripted camera, writes `<project>/benchmark/<timestamp>/{trace.json,summary.json}` and exits. `trace.json` is the existing `Profiler.writeChromeTrace` output (loads straight into Perfetto); `summary.json` extends `writeFrameJson` with p50/p95/p99. `--features` lets one invocation A/B a quality toggle set. **b. Profile outside Play.** Replace the `active and g_record` gate with an explicit off / edit / play source, and honour `TURIAN_PROFILER=1` to force the profiler on in release builds. **c. Per-pass counter attribution.** `Profiler.beginPass(name)` / `endPass()` snapshotting counter deltas into a per-pass row, so `draw_calls` reads `prepass=3880, shadow=824, main=206, transparent=N` instead of one lump. Add `indirect_commands` to `Counters`. **d. Fence-bracketed GPU timing for every pass.** `gpu_timing.zig` already has the pattern; extend it to prepass, SSAO, SSR, main, transparent, post-process and probe bake behind the existing "detailed GPU timing" toggle. Per #147 this is the only GPU timing SDL3 permits (no timestamp-query API on any backend), and it is enough to answer "CPU or GPU bound". ### Files `studio/Main.zig`, `studio/main-window/ProfilerPanel.zig`, `engine/Profiler.zig`, `subsystems/render/gpu_timing.zig`, `subsystems/render/root.zig` ### Acceptance - [ ] `--benchmark` produces a Perfetto-loadable trace and a summary JSON from an unfocused window, with no human interaction - [ ] The Scene viewport can be profiled without entering Play - [ ] Draw calls, triangles and indirect commands are attributed per pass - [ ] Detailed GPU timing reports every pass, not two - [ ] `docs/decisions/bistro-perf-baseline.md` committed with real Bistro numbers