the capability handshake cannot lose a race it never runs

queryTerminal(2ms) blocks on a futex until DA1 comes back, and the number has
to beat one terminal round trip: local answers in microseconds, ssh localhost
under a millisecond, any real link never. Measured against sshd with the
replies delayed to model the wire, 2ms already loses at 5ms RTT.

Losing it is worse than never probing, because vaxis splits detect from enable
and only detect respects the deadline. The flag flips the moment the futex
times out, so the two replies gated on it — explicit width and scaled text,
both spelled as a cursor-position report — stop being read as probe replies and
arrive at the app as shift-F3 and alt-F3 keypresses, while the ungated ones
keep mutating caps from the reader thread long after enable already declined to
switch those modes on. Over ssh the terminal sat in its default modes while
caps claimed otherwise: kitty keyboard was never actually pushed, ever.

So send the probes and resolve them on the loop. DA1 is last and terminals
answer in order, so when the reader flips the flag every earlier reply is
applied — no window to miss at any latency. Verified over real ssh at 5 through
500ms RTT: 7/7 caps and kitty keyboard actually enabled at every one, where
before it was 5/7 and never. Startup is 2ms faster, no golden moves (nothing
answers in the harness, and with no caps enable writes no bytes).

Honest scope: I could not reproduce the reported stale characters, only the
handshake bug behind them. The width half of the theory is inert — vaxis's
Cell.width defaults to 1 and pardes writes one codepoint per cell with an
explicit spacer, so gwidth, the only consumer of caps.unicode, is never called.
That is written down so nobody re-derives it. If the dirty screen survives,
the next suspect is vaxis's own carry-over for an escape sequence split across
a read boundary (Loop.zig:174-190, wrong length and an off-by-one): four wheel
events sent whole scroll four notches, the same four split at a `;` with a
60ms gap scroll zero. Network framing is exactly what makes those gaps. It is
an input bug in a vendored dep and wants its own change.

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