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Reply echo suppression modelled two echo shapes from the spec rather than from
a tty. Captured under node-pty against real bash, at a readline prompt and
under `read`:
- Readline mangles CSI replies, not just OSC: `ESC [ ?` becomes BEL and the
residue echoes. The projection was gated on an OSC introducer, so a private
DSR echo was never matched at a readline prompt. This is the reachable one:
a mode-2031 theme push (`CSI ?997;1n`) left latched by an exited TUI paints
`997;1n` on a bash prompt (#9993's scenario).
- ECHOCTL carets EVERY control, not just ESC. A BEL-terminated OSC reply
echoes as `^G`, but the needle kept a literal BEL — a string no tty
produces. Hardening only: every in-tree OSC reply is ST-terminated
(terminal-osc-color-reply.ts:112, xterm's own reply), so the changed byte
is unreachable except from a foreign or older emulator.
Why this is not the CSI projection #13160 review dropped: that one was the
identity (`replaceAll('\x1b]', …)` is a no-op on a CSI reply), so it was
ESC-led and 500ms-held bare-ESC tails away from the query parser. This one is
BEL-led. The rule is now asserted for every shape rather than implied by the
gate: holdPartial iff the needle does not start with ESC.
The readline branch is keyed on the private-DSR grammar with a non-empty
parameter list, plus a floor on needle length. The containment grammar admits
`CSI ? n`, and `answerLiveQueryReply` takes client-supplied bytes on the relay
path, so a peer could otherwise arm a two-byte `BEL n` needle and delete the
first bell-then-`n` in ordinary output. #61c65151129 proved this system can eat
real output when a needle outlives its budget; a length floor is cheap.
Live coverage: pty-reply-echo-shapes.node-pty.test.ts writes a reply to a real
bash master and feeds back what it echoes, so a shell or libc change fails the
suite instead of silently disarming suppression. Registered in the
shell-contracts lane. The transcript tests and the caretEcho helpers that
encoded the same ESC-only assumption are corrected alongside.
Suppression is display-only. This does not change what reaches the child's
stdin — the reply is written to the master either way, in call order.