Zen-style trace log events (#1006)

Replaces the old (not fully implemented) UE `Logging.*` sink with a typed `ZenLog.*` trace path that preserves structured fmt args end-to-end, so the zen trace analyzer (and future consumers) can re-render log messages with full formatter support.

- Hook `Logger::Log` to tap `fmt::format_args` before `vformat` renders them, and emit three new events on a dedicated `ZenLogChannel`: `Category`, `MessageSpec`, `Message`. Args are serialized as `[count][descriptors][payload]` with distinct categories for bool, int, float, and string. Custom formatters fall back to a pre-rendered string.
- Bool has its own wire category so `{}` renders as `true`/`false` and `{:d}` as `1`/`0`.
- Zen `LogLevel` is translated to UE `ELogVerbosity` on emit so severity filtering works consistently.
- Extend the zen trace analyzer to decode `ZenLog.*` via `fmt::vformat` + `dynamic_format_arg_store` — nested widths, chrono specs, etc. all work. Strings are passed as views directly from the event payload (which outlives the format call) rather than copied through a pool.
- Retire the old `TraceSink` stub; the typed path supersedes it.
- Switch `--trace=default` alias from `cpu,log` to `cpu,zenlog`.
- Add `__int128` overloads to the arg encoder guarded by `FMT_USE_INT128` so fmt's int128 dispatch resolves unambiguously on clang/gcc. MSVC and clang-cl are unaffected.

1 files changed, 7 insertions, 1 deletions

diff --git a/src/zencore/trace.cpp b/src/zencore/trace.cpp
index 6e2eea1c7..2dec0511c 100644
--- a/src/zencore/trace.cpp
+++ b/src/zencore/trace.cpp
@@ -55,7 +55,7 @@ TraceConfigure(const TraceOptions& Options)
 	auto ProcessTraceArg = [&](const std::string_view& Arg) {
 		if (Arg == "default"sv)
 		{
-			ProcessChannelList("cpu,log"sv);
+			ProcessChannelList("cpu,zenlog"sv);
 		}
 		else if (Arg == "memory"sv)
 		{
@@ -70,6 +70,12 @@ TraceConfigure(const TraceOptions& Options)
 			// memtag actually traces to the memalloc channel
 			ProcessChannelList("memalloc"sv);
 		}
+		else if (Arg == "log"sv)
+		{
+			// Upstream UE trace reserves "log" for printf-style Logging.* events, which zen
+			// does not emit. Redirect to the zenlog channel so --trace=log does what users expect.
+			ProcessChannelList("zenlog"sv);
+		}
 		else
 		{
 			// Presume that the argument is a trace channel name