re: the GPU trace is compiled out of the release build -- both my guesses wrong

Last iteration left two candidates for why trace_gpu_stream produced no
file: the CLI flag not reaching the cvar, or BeginTracing failing
silently. Neither. Following the code instead of guessing:

BeginTracing only sets trace_state_ = kStreaming ("Streaming starts on
the next primary buffer execute"). The file is opened later, in
ExecutePrimaryBuffer, inside

  #if XE_ENABLE_TRACE_WRITER_INSTRUMENTATION == 1

and trace_writer.h defines that as 0 under NDEBUG, 1 otherwise -- the
trace writer exists only in debug builds.

Confirmed against the binaries, with a control. The format string
"{:08X}_stream.xtr" lives only inside that guard:

  build/bin/Linux/Release/xenia_canary          0 occurrences
  build/bin/Linux/Debug/xenia_canary            1 occurrence
  /sylph-home/re/canary-build/.../Release/...   0   <- what run-canary uses

The debug binary is the control: it proves the test finds the string when
it is present, so the release zero means something.

So trace_gpu_stream is a no-op in this container's emulator -- the cvar
parses, BeginTracing runs, and nothing can open a file. The kill -9 was
not the cause either, though it would have destroyed a trace had one
existed.

The route exists but is not cheap: a debug build with the writer compiled
in sits at build/bin/Linux/Debug/xenia_canary, 253 MB against Release's
18 MB, so a much slower boot plus a trace of every GPU packet on a disk
at 95%. Recorded as available rather than attempted -- what it would
confirm, the DC_LUT write, is already a well-supported inference, and the
cost is out of proportion to the gain.

METHOD: a cvar existing does not mean the feature is compiled in; and
test a compile-time gate against the binary, with a control.

docs/re/REFUTED.md

@@ -489,3 +489,10 @@ neighbourhood, not just the line.
   `DC_LUT` ramp in the swap path. No emulator-side gamma post-process exists to
   subtract. 🟡 Whether this game installs a ramp at all is still unestablished.
   [`ui-render-tone-curve.md`](structures/ui-render-tone-curve.md)
+* "the GPU trace produced nothing because either the CLI flag did not reach the
+  cvar or `BeginTracing()` failed silently" → **both wrong.** The trace writer is
+  **compiled out**: `trace_writer.h` gates it on `#ifdef NDEBUG`, so a release
+  build has no writer at all. Confirmed with a control — the format string
+  `_stream.xtr` appears **once** in the Debug binary and **zero** times in the
+  Release binary `run-canary` actually uses.
+  [`capture-harness-status.md`](capture-harness-status.md)