The startup graphics probe only ran on ConPTY hosts with WT_SESSION, so a
SIXEL-capable terminal that exposes no identifying environment variable
(foot exports TERM=foot and COLORTERM=truecolor only) resolved the
trueColor capability row, kept imageProtocol null, and rendered every
image as the "[Image: …]" text card.
The XTSMGRAPHICS branch also had its status inverted: per xterm ctlseqs a
reply of `CSI ? 2 ; Ps ; Pv S` carries Ps = 0 on success, and a terminal
without SIXEL reports a zero maximum geometry, so a successful reply was
read as unsupported.
Drop the dead DA1 half of the probe with it: ProcessTerminal swallows
every `CSI ? … c` reply for the whole session so a late one cannot leak
into the composer (#8542), which means the attribute list never reached
the probe's input listener on any platform. The bare `CSI c` it wrote was
also unaccounted for in the DA1 sentinel FIFO, so its reply consumed
another probe's sentinel.
PI_FORCE_IMAGE_PROTOCOL, including its off/none kill switch, still wins
over the probe.
Kenneth Watson
49543d798e