fix(locale): strip POSIX encoding suffix from macOS locale vars to prevent ICU crash

[tpaustin]

Summary

• Strips POSIX encoding suffixes (e.g. .UTF-8) from locale env vars after initialization on macOS, catching values from any source (existing env, shell detection, or fallback)
• Changes getFallbackUtf8Locale() on darwin to return en_US instead of en_US.UTF-8
• Updates LSEnvironment in package.json to use en_US so the Info.plist value is also ICU-safe before any JS runs
• Updates tests to reflect the suffix-stripped expectations on macOS

Background

Issue #1633 reports that Emdash crashes on launch on macOS 26+ starting from 0.4.44, and the crash persists through 0.4.45.

The crash stack is:

libicucore    uloc_getTableStringWithFallback  ← null pointer dereference
Foundation    Locale.characterDirection(forLanguage:)
UIFoundation  +[NSParagraphStyle _defaultWritingDirection]
AppKit        +[NSApplication _defaultUserInterfaceLayoutDirection]
AppKit        -[NSCocoaMenuImpl initWithMenu:]

Root cause: ICU's uloc_getTableStringWithFallback on macOS 26+ crashes when it receives a locale string with a POSIX encoding suffix like .UTF-8. ICU expects bare locale identifiers (en_US, not en_US.UTF-8). On older macOS, Foundation silently stripped the encoding suffix before passing it to ICU; on macOS 26 this stripping no longer happens.

PR #1632 changed the fallback from C.UTF-8 to en_US.UTF-8, and PR #1640 added LSEnvironment with en_US.UTF-8 — but any .UTF-8 suffix triggers the same crash. macOS always uses UTF-8 regardless of locale, so the suffix is both redundant and harmful.

Compatibility: The fix is fully backwards compatible. Stripping .UTF-8 from en_US.UTF-8 → en_US is semantically a no-op on macOS (all macOS locales are UTF-8). Older macOS versions tolerated the suffix; newer ones do not. The stripped value is what ICU always expected.

Test plan

• pnpm exec vitest run src/main/utils/__tests__/shellEnv.test.ts — all 15 tests pass
• pnpm exec vitest run — all 863 tests pass
• pnpm run build passes
• pnpm run type-check passes
• App launches without crash (pnpm run dev — confirmed clean startup with no segfault)

Closes #1633

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Enhanced macOS locale and language environment variable handling by normalizing locale identifiers to properly align with macOS system requirements, improving overall system compatibility and ensuring consistent behavior across different language and regional configurations
  • Refined how environment variables for locale-dependent features are configured to provide better support for regional customization and language settings on macOS

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 74386456-bb72-4920-9eb5-0163b933f907

📥 Commits

Reviewing files that changed from the base of the PR and between 6a89f67 and 3039d33.

📒 Files selected for processing (3)

• package.json
• src/main/utils/__tests__/shellEnv.test.ts
• src/main/utils/shellEnv.ts

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📝 Walkthrough

Walkthrough

The pull request updates macOS locale environment variable handling to strip POSIX encoding suffixes. Changes include modifying build configuration to use en_US instead of en_US.UTF-8, adding a platform-specific sanitization function to remove encoding suffixes from locale values, and updating tests to reflect platform-dependent locale formatting expectations.

Changes

Cohort / File(s)	Summary
Build Configuration package.json	Modified macOS extended Info settings to change LANG and LC_CTYPE locale values from en_US.UTF-8 to en_US.
Shell Environment Utilities src/main/utils/shellEnv.ts	Added sanitizeLocaleForPlatform() helper to strip POSIX encoding suffixes (e.g., .UTF-8) on macOS. Updated getFallbackUtf8Locale() to return en_US instead of en_US.UTF-8. Extended initializeShellEnvironment() to sanitize locale environment variables on macOS.
Shell Environment Tests src/main/utils/__tests__/shellEnv.test.ts	Updated locale expectations to be platform-dependent: macOS tests use stripped locale values (e.g., C, en_US), while non-macOS tests use UTF-8 suffixed values. Added strip() helper for test-specific locale normalization.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Possibly related PRs

• fix: macos crashing since 0.4.43 #1640: Directly related—both PRs modify macOS locale handling in LSEnvironment configuration and shell environment initialization.
• fix(locale): avoid macOS startup crash from C.UTF-8 fallback #1632: Directly related—both PRs adjust getFallbackUtf8Locale() and test expectations for Darwin platform locale behavior.
• fix(pty): preserve UTF-8 locale for embedded terminals #1626: Related—both PRs modify shell environment locale handling; this PR adds macOS-specific encoding suffix stripping while the other implements broader UTF-8 locale normalization.

Poem

🐰 Locale suffixes gone with a swish,
macOS gets its .UTF-8 wish,
en_US strips bare and clean,
The smoothest environment we've seen! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: fixing locale environment variables on macOS by stripping POSIX encoding suffixes to prevent ICU crashes.
Linked Issues check	✅ Passed	The PR directly addresses issue #1633 by fixing the segfault caused by locale strings with POSIX encoding suffixes, implementing the root cause fix across shell environment initialization, fallback locale, and package.json configuration.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the macOS locale/ICU issue: package.json LSEnvironment values, locale sanitization logic, fallback locale behavior, and corresponding test updates.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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