brush-core's alias expander resolves aliases via
`value.split_ascii_whitespace()` (`crates/brush-core-vendored/src/interp.rs:1500`,
upstream brush issue reubeno/brush#57): each whitespace piece is dropped
into argv as-is, completely bypassing the shell parser. Any alias body
containing `(`, `)`, `|`, `&`, `;`, `<`, `>`, or `\`` therefore
turns the first piece into the command name, so Fedora's default
`alias which='(alias; declare -f) | /usr/bin/which …'` produces
`error: command not found: (alias;` for every `which` invocation.
The user's shell snapshot is generated by sourcing their real rc-file
under `/bin/bash` or `/bin/zsh` (so we can capture functions, options,
PATH) and then sourced by brush per-session. `sanitizeSnapshotForBrush`
now scans the emitted `alias -- NAME='VALUE'` lines after generation,
drops any whose decoded body contains those metacharacters, and rewrites
the file in place before caching. Compatible aliases (`ll='ls -l'`,
`gc='git --color=auto commit'`, embedded-quote `say='echo '\\''hi'\\'''`)
are preserved untouched; dropped names are logged at debug. brush then
falls through to whatever lives on `PATH`, which is what the user
expected when they ran `which` in the first place.
Covered by unit tests for the sanitizer (Fedora-which case, every
incompatible-metachar shape, every preserve case) and an integration
test that loads a poisoned snapshot and verifies `which sh` now exits
`0` with a real path.
Fixes#3234
roboomp
58fab73699