fix(desktop): agent shells inherit a UTF-8 locale on macOS

[Linus-Boehm]

Fixes #6231.

GUI-launched macOS apps inherit no LANG/LC_* from launchd, so agent CLIs spawned by the desktop app ran in the C locale. pbcopy decodes stdin using the locale encoding rather than passing bytes through, so any non-ASCII text an agent copied was silently corrupted — Grüße – ß arrived as Grüße – ß.

DesktopShellEnvironment already resolves the login shell environment into process.env, which the backend and its agent CLIs inherit. Its allowlist just didn't include the locale. This adds LANG/LC_ALL/LC_CTYPE to the harvest and the existing copy-if-absent pass, then falls back to C.UTF-8 on macOS when neither the process nor the login shell supplies one.

C.UTF-8 rather than the user's full locale on purpose: it fixes the codeset without shifting collation or formatting, so anything parsing tool output is unaffected (sort gives a b ä under C.UTF-8 but a ä b under de_DE.UTF-8). It's also what macOS's own /etc/zprofile falls back to — env -i HOME=$HOME /bin/zsh -ilc 'echo $LANG' returns C.UTF-8. LC_ALL is harvested but never force-set, since it would override every LC_* category.

Scoped to the desktop spawn path. A standalone server started without a locale would have the same problem, but that's a separate concern and I've left it out to keep this small.

Verification: 4 new tests in DesktopShellEnvironment.test.ts (harvest, inherited-value precedence, macOS fallback, no-fallback-on-linux); the two behavioural ones fail without the source change. vp test green for @t3tools/desktop (448 tests), typecheck and fmt --check clean.

No UI change, so no screenshots.

Written with Claude Opus 5, via the Claude Code CLI running inside T3 Code.

Note

Fix agent shells to inherit a UTF-8 locale on macOS

• Adds LANG, LC_ALL, and LC_CTYPE to the login shell environment whitelist in DesktopShellEnvironment.ts so they can be hydrated from the login shell.
• On macOS, if no locale variables are present in the process environment, they are hydrated from the login shell; if still absent, LC_CTYPE falls back to en_US.UTF-8.
• If any locale variable is already inherited, it is preserved and login-shell locale values are not mixed in. This fallback does not apply on Linux.
• Behavioral Change: macOS agent shells that previously inherited no locale will now always have at least LC_CTYPE=en_US.UTF-8 set.

^{Macroscope summarized dee3e06.}

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Note

Low Risk
Scoped macOS-only environment hydration with careful precedence and a UTF-8 LC_CTYPE fallback; no auth or data-path changes.

Overview
Fixes GUI-launched macOS agent shells landing in the C locale, which caused pbcopy to corrupt non-ASCII text.

DesktopShellEnvironment now harvests LANG/LC_ALL/LC_CTYPE from the login shell and hydrates them as a group only when the process has none. If still unset on macOS, it falls back to LC_CTYPE=en_US.UTF-8 (leaving LANG unset to keep C-stable collation/formatting). Inherited locales are preserved and not mixed with login-shell categories; Linux is unchanged.

^{Reviewed by Cursor Bugbot for commit dee3e06. Bugbot is set up for automated code reviews on this repo. Configure here.}

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[macroscopeapp]

Approvability

Verdict: Approved dee3e06

This is a targeted macOS bug fix that adds UTF-8 locale fallback handling for GUI-launched shells. The change is conservative (only applies when no locale is already set), platform-specific, and well-tested with 5 new test cases.

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