Testing shells end-to-end

Patterns for functionally driving omp's shell integrations, mostly in WSL (verified on aarch64, zsh 5.9, fish 4.1.2).

WSL basics

WSL /tmp is wiped between separate wsl.exe invocations (instance auto-shutdown). Either make a test fully self-contained in ONE wsl -e call, or stage everything under $HOME (e.g. ~/omp-test).
From Git Bash, prefix MSYS_NO_PATHCONV=1 so /mnt/c/... arguments reach wsl.exe unmangled.
Build for WSL either inside WSL (/usr/local/go/bin/go) or cross-compile from Windows (GOOS=linux GOARCH=arm64). Shell scripts are embedded at build time - rebuild after every script edit, then regenerate the sourced init with oh-my-posh init <shell> --print.
Differential testing: build the control binary from git show HEAD:<file> or via git stash push -- <file>; the fixed binary from the working tree.
pkill -f <pattern> matches its own caller's command line when inlined - pick patterns that cannot appear in the runner script.

zsh -i under plain wsl -e hangs before the first prompt (no foreground pty). Options:
- wsl -e script -qec 'zsh -i' /dev/null - real pty, MONITOR enabled, job-control behavior testable. Run backgrounded with output to a file and poll a done-marker; foreground runs can wedge under the wsl relay.
- zmodload zsh/zpty in a driver zsh - best for keystroke-level scenarios: zpty omp zsh -i, write raw keys with zpty -w -n omp $'\x03' (Ctrl+C delivers a real SIGINT through the pty), assert via state files written by in-session commands, drain output with zpty -r after exit. Note script(1) does NOT work inside zpty (typescript never appears).
Per-shell script(1) quirks: bash prompt bytes are not relayed to stdout (probe ${PS1@P} in-session); fish discards piped typeahead (in-session probes never run); zsh relays fine.
Do not test the zsh serve path from a non-interactive zsh script.zsh - it hangs in read -u fd -d $'\0' -t N (the -t is ignored with -d, see zsh).

Harness pattern (built for #5992): stage a binary, config, zdot dirs, and zpty driver scripts under $HOME in WSL; one driver runs mode-aware ESC/Enter/Ctrl+C scenarios into a state log, another asserts the transient prompt renders. Always compare a fixed run against a control zdot (same setup, feature under test disabled).
Keep probes mode-aware: with zsh-vi-mode, a line after a normal-mode accept starts in normal mode - prefix typed commands with i where needed, and remember a stray self-inserted i turns the probe into a failing command (useful as a broken-state detector: last_status=127).

There is no shell-command segment type. To hold omp stream/a render open for a controllable window, point an http segment at a silent local TCP listener (python3 -c 'socket...accept...sleep') with a large http_timeout; kill the listener to trigger the async update record.

One bufio.Scanner per pipe, ever - a second scanner on the same pipe loses buffered data (use a shared reader helper in Go tests).