fix(desktop): ensure UTF-8 locale in macOS terminals

[Kiri110K]

What Changed

Terminals opened in the macOS desktop app ran with a US-ASCII character locale instead of UTF-8.

The POSIX login-shell probe now also reads LANG, LC_ALL and LC_CTYPE, and hydrates whichever of them the launch environment is missing. If macOS still reports no character locale after that, LC_CTYPE falls back to the platform-native UTF-8 value — the same value Terminal.app uses when a region has no matching locale. Values already present in the launch environment always win. Linux gets the hydration but never the fallback, and Windows is untouched.

Why

Apps launched from Finder inherit no LANG or LC_* variables. macOS then defaults to US-ASCII, so zsh's line editor edits multi-byte input byte by byte: one backspace deletes half of a Cyrillic or accented character, and any tool that reads the locale picks an ASCII encoding.

Reading the login shell first, rather than jumping straight to the fallback, keeps the user's own locale intact — someone running ru_RU.UTF-8 keeps their language, collation and messages instead of being flattened to a bare UTF-8 ctype. The fallback only fills a gap nobody else filled, and only sets the character category, so it never overrides a language the user did choose.

On surfaces: npx t3 is started from a terminal and already inherits the locale, so the Electron launch path was the only broken one. Because the desktop app is also commonly the host server, web and mobile clients connected to it get the same fix in the terminals they open.

Verification

Before and after, reproducible on any Mac without the app:

$ env -i /bin/zsh -c 'locale charmap'
US-ASCII
$ env -i LC_CTYPE=UTF-8 /bin/zsh -c 'locale charmap'
UTF-8

zsh, bash, perl and locale all accept the bare UTF-8 ctype on Darwin without emitting warnings.

Four focused tests cover the behaviour: the fallback when the launch environment has no locale, hydration from the login shell, launch-environment values winning over the shell's, and Linux not receiving the fallback.

apps/desktop tests pass (518) and tsgo --noEmit for that package is clean.

UI Changes

Not applicable; this change has no UI surface.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes (not applicable; no UI changes)
• I included a video for animation/interaction changes (not applicable; no animation or interaction changes)

Implemented with GPT-5.6-Sol using the Codex harness in T3 Code.

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Note

Low Risk
Startup-time env patching for embedded terminals only; inherited locales win and behavior is covered by focused tests with no auth or data-path changes.

Overview
Fixes US-ASCII terminals when the macOS desktop app is launched without LANG/LC_* (e.g. from Finder) by extending the POSIX login-shell environment install in DesktopShellEnvironment.

The login-shell probe now captures LANG, LC_ALL, and LC_CTYPE. If the launch environment has no non-empty locale among those three, the shell values are applied as a set so a shell LC_ALL cannot override an inherited LANG. Any locale already present in the launch environment is left unchanged. On darwin only, if there is still no locale after probing, LC_CTYPE is set to UTF-8; Linux gets hydration only, with no fallback.

Four tests cover fallback, shell hydration, inherited-locale precedence, and Linux not receiving the fallback.

^{Reviewed by Cursor Bugbot for commit 23981d7. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Fix UTF-8 locale handling in macOS terminals when no locale is inherited

• Extends login shell probing in DesktopShellEnvironment.ts to include LANG, LC_ALL, and LC_CTYPE.
• When none of these locale variables are present in the launch environment, all three are hydrated as a group from the login shell output.
• On macOS, if no locale variables are found after hydration, LC_CTYPE is explicitly set to 'UTF-8' to guarantee UTF-8 character handling.
• An existing LANG in the launch environment is never overridden by a login shell LC_ALL, preventing silent locale downgrades.

^{Macroscope summarized 23981d7.}

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[macroscopeapp]

Approvability

Verdict: Approved 23981d7

This is a well-scoped bug fix that ensures UTF-8 locale handling for macOS Finder-launched apps. The implementation is defensive (only applies when no locale exists), limited to locale variables, and has comprehensive test coverage.

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[Kiri110K]

Oups, was already done in #6236