fix(pty-proxy): resolve SHELL path in proxied zsh sessions

[hangrymuppet]

Fixes self-reported #3606; regression introduced after #3548

Thank you for maintaining this awesome piece of work!

Checks

• I am happy for maintainers to push small adjustments to this PR, to speed up the review cycle
• I have checked that there are no existing pull requests for the same thing

[github-actions]

Fossier: Manual Review Requested

@hangrymuppet is a new contributor. A maintainer should review this PR before merging.

Score Breakdown

Total Score: 58.2/100 | Confidence: 74% | Outcome: REVIEW

Signal	Value	Score	Weight
account_age	4397	1.00	0.09
public_repos	32	1.00	0.05
contribution_history	37	0.18	0.05
follower_ratio	0.0	0.00	0.05
bot_signals	False	0.50	0.04
open_prs_elsewhere	0	FAILED (Search failed)	0.09
closed_prs_elsewhere	0	FAILED (Search failed)	0.10
merged_prs_elsewhere	0	FAILED (Search failed)	0.08
prior_interaction	0	0.00	0.08
activity_velocity	0	1.00	0.08
pr_content	...	1.00	0.08
commit_email	no_email	0.50	0.04
pr_description	...	0.70	0.05
repo_stars	30518	0.30	0.04
org_membership	0	0.20	0.03
commit_verification	...	1.00	0.04
contributor_stars	0	0.00	0.04

[greptile-apps]

Greptile Summary

This PR changes how proxied zsh sessions choose the shell path. The main changes are:

• Normalize ZSH_ARGZERO before forwarding it.
• Prefer a matching executable $SHELL for bare zsh names.
• Fall back to resolving the zsh name through command -v.
• Update the generated-script unit test expectations.

Confidence Score: 4/5

The changed flow looks mergeable after tightening the zsh path selection.

• The generated script can prefer $SHELL by basename when it may not be the zsh binary that launched the current session.
• The issue is limited to zsh setups with multiple installed zsh paths or a stale login shell value.

crates/atuin-pty-proxy/src/pty_proxy.rs

Important Files Changed

Filename	Overview
crates/atuin-pty-proxy/src/pty_proxy.rs	Updates zsh shell-path resolution in the generated pty-proxy init script and adjusts string-based tests.

_{Reviews (1): Last reviewed commit: "fix(pty-proxy): resolve SHELL path in pr..." | Re-trigger Greptile}

[poliorcetics]

Suggested change

	let shell_path = if let Some(ref path) = options.shell {
	if path.is_absolute() {
	Some(path.clone())
	} else if let Ok(paths) = std::env::var("PATH") {
	// Resolve via $PATH
	std::env::split_paths(&paths)
	.map(|p| p.join(path))
	.find(|p| p.is_file())
	// Fallback if not found in $PATH
	.or_else(|| Some(path.clone()))
	} else {
	// No $PATH variable
	Some(path.clone())
	}
	} else {
	// No shell specified
	None
	};
	let shell_path = match options.shell {
	Some(ref path) => if path.is_absolute() {
	Some(path.clone())
	} else if let Ok(paths) = std::env::var("PATH") {
	// Resolve via $PATH
	std::env::split_paths(&paths)
	.map(|p| p.join(path))
	.find(|p| p.is_file())
	// Fallback if not found in $PATH
	.or_else(|| Some(path.clone()))
	} else {
	// No $PATH variable
	Some(path.clone())
	}
	// No shell specified
	None => None,
	};

Or even use options.shell.as_ref().map(|path| { /* ... */ }) maybe ?

[poliorcetics]

Suggested change

	let ppid = unsafe { libc::getppid() };
	let ppid = std::os::unix::process::parent_id();

[poliorcetics]

With this change it's also possible to make the libc dep macos-only, see https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies

[poliorcetics]

Could you add // Safety: comments on every unsafe block ?

[poliorcetics]

Suggested change

	if let Some(path) = path
	&& let Some(detected_shell) = shell_from_name(&path.to_string_lossy())
	&& detected_shell == target_shell
	{
	return Some(path.to_string_lossy().into_owned());
	}
	if let Some(path) = path
	&& let path = path.to_string_lossy()
	&& let Some(detected_shell) = shell_from_name(&path)
	&& detected_shell == target_shell
	{
	return Some(path.into_owned());
	}

Avoids doing the to_string_lossy() twice (which does a UTF-8 check each time)