Unix PowerShell emits cursor-position requests while PSReadLine starts and
redraws prompts. The subprocess PTY is only a transport, so those requests
went unanswered. Startup could then accept the dsh> literal echoed from its
setup source as a rendered prompt, and later sends were lost or clipped.
Feed raw PTY output into a zero-scrollback @xterm/headless state machine and
write generated replies through the provider-owned terminal handle. Drain
replies before caller input, repeat foreground inspection when terminal
activity races the sample, and retain send ownership until parser and reply
work quiesce. Coalesce raw chunks behind one active parser write so large
Windows output cannot create thousands of queued parse callbacks.
Publish pwsh only from backend stdin_read evidence and start one timeoutMs
deadline before the complete startup retry loop, so inferred-idle follow-ups
cannot reset the bound. Dispose the emulator when the
terminal or cleanup fails. Document the fail-loud ConstrainedLanguage path
and add focused coverage for split queries, reply ordering, foreground
resampling, failure containment, batching, timeout, and disposal.
tool-bash-persistent overwrote the backend's PS1, so terminal-bash prompt
readiness never matched and every send degraded to the 3.5s silence tier
(idleSilenceMs + handoffGraceMs) under production defaults.
The controlled PROMPT_COMMAND now re-asserts PS1 before every prompt, so an
in-shell override never survives to the next prompt. The tool initializes
with stty -echo alone and detects the no-end-marker fallback through the
seam's stdin_read wait reason instead of matching its own prompt text.
Tool calls drop from 7180/3560/3566 ms to 355/88/91 ms (spawn+init+echo,
echo, pwd; darwin, production defaults). The loader composition suite now
pins the fast path by pushing idleSilenceMs beyond the send bound, and a
real-PTY case proves PS1 self-healing.
Fixes#2585
Tianyi Cui