Measure startup, and find there is nothing in it worth optimizing

A --startup case in the perf harness times Pardes.init and the first frame for
each boot layout, with the same --json and --base shape as the others, so these
are a baseline rather than a one-off reading. The core boots and paints in
0.22 ms (tty) to 0.30 ms (classic): about one percent of what starting the
editor costs, and nothing to win.

The other 99% is one thing, found with perf record rather than guessed at.
Zig's start.main allocates through the Debug-mode DebugAllocator, which
captures a six-frame stack trace per allocation, and the first capture parses
and sorts the DWARF unwind tables of an 800 MB binary -- 22% of all samples sit
in mem.swap under that pdq sort. It is not the dynamic loader (25 us), not
static initializers (the binary has no .init_array), not paging (435 page
faults), and not lockStderr. std/start.zig:694 hardcodes DebugAllocator(.{}),
so there is no knob short of the build mode.

Controls that pin it down: a bare std.process.Init hello-world starts in 3 ms,
the ReleaseFast pardes-perf binary in 4 ms, /bin/true in 1 ms, and a Debug
pardes in 22 ms. The gui binary's 107 ms first run was cold page cache; warm it
matches the tty one.

So the conclusion recorded in features.txt is to leave it alone. Twenty-two
milliseconds is imperceptible for an editor, and the only lever is switching
the default build mode, which would multiply an already ten-minute build to
save eighteen milliseconds of startup.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

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