Auto-compact writes `/compact <prompt>\r` through writeViaMux when the token
count crosses the threshold, unattended. AutoCompactSchema.prompt accepts line
breaks, so a prompt set through the API can hold several lines. The mux used to
strip them and run the lines together; it now pastes multi-line text as one
block, and the check that re-presses a stranded Enter cannot recognise that
paste in the composer. That is the case respawn's update and kickstart prompts
were already joined for.
The join moves out of respawn-controller into a shared toSingleLine()
(src/utils/single-line.ts), used by both respawn steps and by auto-compact.
Behaviour for respawn is unchanged. The respawn test file becomes
test/unattended-single-line-prompt.test.ts and gains an auto-compact block that
feeds a real Session a token count over its threshold and reads what reaches
writeViaMux.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>