fix(windows): resolve ERROR_UNTRUSTED_MOUNT_POINT (448) for junction and symlink working directories

[OthmanAdi]

Description

Fixes #9044

On Windows, when the configured working directory (or its fallback, USERPROFILE) contains or is a junction point or reparse point, CreateProcessW fails with ERROR_UNTRUSTED_MOUNT_POINT (WinError 448). This breaks symlink traversal for the shell and all child processes, including Get-ChildItem, pytest, and any tool that resolves through junctions.

The same commands work correctly in Windows Terminal and standalone PowerShell because they pass canonicalized paths to CreateProcessW.

Root cause: In app/src/terminal/local_tty/windows/mod.rs (line 176), the start_dir is validated only with is_dir() and then passed directly as lpCurrentDirectory to CreateProcessW without canonicalization. Junction points pass the is_dir() check but fail inside the kernel's path resolution for untrusted mount points.

Fix: Call dunce::canonicalize() on both the configured start_dir and the USERPROFILE fallback before passing them to CreateProcessW. This resolves symlinks, junctions, and reparse points to their actual paths, eliminating the 448 error.

The dunce crate is already a dependency in the app crate and is used for the same purpose in working_directories.rs (line 745), available_shells.rs (lines 818, 850), standardized_path.rs (line 99), and login_item/windows.rs (line 77).

What this changes

Before	After
start_dir passed raw to CreateProcessW	dunce::canonicalize(start_dir) resolves junctions first
USERPROFILE fallback passed raw	USERPROFILE also canonicalized
Junction directories cause error 448	Junction directories resolve to their target and work

Testing

• cargo check -p warp passes clean
• Manual testing on Windows 11:
  1. Create a junction: New-Item -ItemType Junction -Path "C:\Users\oasrvadmin\AppData\Local\Temp\warp_test" -Target "C:\Users\oasrvadmin\Documents"
  2. Set Warp startup directory to the junction path
  3. Before fix: CreateProcessW fails with error 448
  4. After fix: shell spawns normally, Get-ChildItem works through the junction

No new automated tests added because this fix is in the Windows ConPTY spawn path, which requires a running ConPTY session to test. The dunce::canonicalize function itself is well tested upstream.

Server API dependencies

• N/A

Agent Mode

• Warp Agent Mode

Changelog Entries for Stable

CHANGELOG-BUG-FIX: Fixed OS Error 448 (ERROR_UNTRUSTED_MOUNT_POINT) on Windows when the working directory contains symlink or junction points.

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@OthmanAdi

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[oz-for-oss]

Overview

This PR canonicalizes the Windows PTY start directory and USERPROFILE fallback before passing them to CreateProcessW, addressing failures when the configured working directory is a junction, symlink, or other reparse point.

Concerns

• No blocking correctness, error-handling, performance, or security concerns found in the changed lines.

Verdict

Found: 0 critical, 0 important, 0 suggestions

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[vorporeal]

Hi @OthmanAdi - do you know why your commit is showing up as "unverified"? The fact that the tooltip for it says "This commit is not signed, but one or more authors requires that any commit attributed to them is signed." is concerning.

[OthmanAdi]

Hey @vorporeal, thanks for catching that. I didn't have commit signing configured on this machine. Setting it up now and will push signed commits shortly.

[OthmanAdi]

@cla-bot check

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The cla-bot has been summoned, and re-checked this pull request!