Make pty/run and /log streams, and take refused lines back cleanly

Review fixes to pty/run and /log:

- Both are streams with a per-open cursor. A shell's exec 3<>file shares
  one offset between write and read, so cat <&3 after echo make >&3 asked
  for offset 5 and got "0" instead of "exit 0"; log after follow lost its
  first bytes the same way.
- A run is accepted only in pardes's own tagged input phase, so a nested
  shell's prompt (ssh, a shell with its own integration) is never taken for
  this shell's.
- A line the shell refused is taken back so the next finds the prompt
  clear: bash's continuation prompt (now tagged k=c) gets Ctrl-C and the
  answer waits for the fresh prompt; a bash syntax error (no C, but a D) is
  answered at once; fish's kept line gets Ctrl-U (a Ctrl-C sent while fish
  redraws is lost). fish's right prompt no longer reads as typed input.
- bash marks a command's start from PS0 on bash 4.4+, not a DEBUG trap, so
  a user's own DEBUG trap (bash-preexec, atuin) survives. bash's own job
  notices now show as in plain bash (ttyfollow golden).
- 32 run slots; a new line on an open starts a fresh answer.

Checked live in bash, fish, and fish with a right prompt.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 6 insertions, 1 deletions

diff --git a/src/host_io.zig b/src/host_io.zig
index fcd2225b..34c2f57a 100644
--- a/src/host_io.zig
+++ b/src/host_io.zig
@@ -589,8 +589,13 @@ pub const Shell = struct {
     const bash_rc =
         \\[ -f "$HOME/.bashrc" ] && source "$HOME/.bashrc"
         \\PS1='\[\e]133;A;cl=line;aid=pardes\a\]'"$PS1"'\[\e]133;B;aid=pardes\a\]'
+        \\PS2='\[\e]133;A;k=c;aid=pardes\a\]'"$PS2"'\[\e]133;B;aid=pardes\a\]'
         \\PROMPT_COMMAND='printf "\e]133;D;%s;aid=pardes\a" "$?"'"${PROMPT_COMMAND:+;$PROMPT_COMMAND}"
-        \\trap 'printf "\e]133;C;aid=pardes\a"' DEBUG
+        \\if ((BASH_VERSINFO[0] * 100 + BASH_VERSINFO[1] >= 404)); then
+        \\    PS0='\e]133;C;aid=pardes\a'"$PS0"
+        \\else
+        \\    trap 'printf "\e]133;C;aid=pardes\a"' DEBUG
+        \\fi
         \\
     ;