Launch crash on macOS 27.0 beta (26A5378j): CoreUI exception (CUINamedVectorGlyph) in first layout — triggered by comma-decimal LC_NUMERIC locale (0.64.17 + nightly)

[b80k]

Environment

• cmux 0.64.17 (97) — crash also reproduces identically on 0.64.17-nightly.2914190390601 (downloaded today)
• macOS 27.0 beta (26A5378j), Mac16,7 (arm64)
• Multi-display setup (built-in 2056×1289 + external 5120×1409)

Summary

cmux crashes ~1 s after launch with EXC_BREAKPOINT via +[NSApplication _crashOnException:]. The underlying uncaught ObjC exception is thrown by CoreUI in -[CUINamedVectorGlyph _rasterizeImageUsingScaleFactor:forTargetSize:renderingMode:colorResolver:] while SwiftUI renders SF Symbols during the first layout pass of the session-restore main window:

AppDelegate.createMainWindow(…sessionWindowSnapshot:…) → makeKeyAndOrderFront → -[NSWindow _setUpFirstResponderBeforeBecomingVisible] → NSHostingView.layout → renderVectorGlyph → CoreUI throw.

The interesting part: it is deterministic, gated on launch activation

15 launches on the same machine, same morning:

Launch method	Result
Finder/Dock icon (double-click)	crash 6/6
AppleScript applet wrapping open -g -a cmux (with and without a 3 s detached delay)	crash 4/4
open -g -a cmux typed in a terminal that stays frontmost	survives 5/5

Independent of time since wake (one crash cluster at wakeTime: 4211 s, another at 4998 s, successful launches in between and after).

Observed behavior in the applet case: the applet exits, and focus then lands "by itself" on the half-started cmux — i.e. cmux self-activates during bootstrap (consistent with #3215 and #3347). Whenever macOS grants that self-activation (any GUI-initiated launch), the restore window's first symbol-heavy layout runs in the key/visible configuration and CoreUI throws. When macOS denies it (an actively used terminal stays frontmost), the same code path completes fine. This looks directly related to the activation-vs-window-ordering handling in Sources/App/MainWindowVisibilityController.swift (ActivationTiming, respectActivationSuppression).

Not state-related

• No zero-size window frames in defaults read com.cmuxterm.app
• The same persisted session snapshot restores fine on every non-activating launch
• cf. 0.63.0 crashes on launch on macOS 26.3.1 (25D771280a) even after clearing all saved state #2309 — clearing all saved state did not help that reporter either

Prior art

• Fix launch crash on macOS 27 from zero-size SF Symbol rasterization #5670 (v0.64.15), Fix macOS 27 SF Symbol rasterization crash #5999 (v0.64.16), Fix blank SF Symbol controls on macOS 27 #6396 (v0.64.17) fixed "zero-size SF Symbol rasterization on macOS 27" — this activating-launch restore path is apparently still uncovered
• Crash on launch: exclusive access violation in windowDragHandleShouldCaptureHit #490 — earlier launch crash that also reproduced only on activating launches
• new-workspace activates cmux app, stealing macOS focus from other apps #3215 / cmux always reports as macOS frontmostApplication, breaks focus-follows-mouse #3347 — cmux's self-activation behavior

Crash backtrace (excerpt)

Application Specific Backtrace (0.64.17 (97), 26A5378j)

0   CoreFoundation        __exceptionPreprocess + 176
1   libobjc.A.dylib       objc_exception_throw + 88
2   Foundation            -[NSCalendarDate initWithCoder:] + 0   (symbolication artifact)
3   CoreUI                -[CUINamedVectorGlyph _rasterizeImageUsingScaleFactor:forTargetSize:renderingMode:colorResolver:] + 184
4   CoreUI                __64-[CUINamedVectorGlyph _imageForRenderingMode:withColorResolver:]_block_invoke + 1316
7   CoreUI                -[CUINamedVectorGlyph image] + 124
8   RenderBox             RB::Symbol::Presentation::template_image() + 540
10  SwiftUICore           _ShapeStyle_RenderedContext.renderVectorGlyph(...) + 436
22  SwiftUICore           GraphHost.flushTransactions() + 864
25  SwiftUI               NSHostingView.layout + 484
48  AppKit                -[NSView layoutSubtreeIfNeeded] + 96
51  AppKit                -[NSWindow _setUpFirstResponderBeforeBecomingVisible] + 68
52  AppKit                -[NSWindow _doWindowWillBeVisibleAsSheet:] + 112
56  AppKit                -[NSWindow makeKeyAndOrderFront:] + 40
57  cmux                  AppDelegate.createMainWindow(initialWorkspaceTitle:...sessionWindowSnapshot:...shouldActivate:...) + 14304
58  cmux                  AppDelegate.ensureInitialMainWindowIfNeeded(shouldActivate:suppressWelcome:) + 1076
59  cmux                  AppDelegate.bootstrapInitialMainWindowIfNeeded(debugSource:shouldActivate:suppressWelcome:) + 132
60  cmux                  closure #1 in AppDelegate.scheduleInitialMainWindowBootstrap(debugSource:) + 196

Full .ips reports (10 crashes, release + nightly) available on request.

Happy to test a fix build or a nightly — this machine reproduces the crash 100% reliably via icon launch.

[b80k]

Trigger isolated (2026-07-12): comma-decimal LC_NUMERIC in the process environment.

Minimal repro on the affected machine (macOS 27.0 beta 26A5378j, M4 Pro, German system locale):

env -i HOME="$HOME" USER="$USER" PATH=/usr/bin:/bin LANG=en_US.UTF-8 LC_NUMERIC=de_DE.UTF-8 /Applications/cmux.app/Contents/MacOS/cmux   # crashes ~1s in
env -i HOME="$HOME" USER="$USER" PATH=/usr/bin:/bin LANG=de_DE.UTF-8 LC_NUMERIC=en_US.UTF-8 /Applications/cmux.app/Contents/MacOS/cmux   # runs

Evidence matrix (each row = independent launches, identical direct-binary start mechanism, 12 s survival probe + crash-report count):

process env	result
env -i minimal (no LANG → system locale de_DE)	3/3 crash
full shell env incl. LANG=en_US.UTF-8	alive
env -i + LANG=en_US.UTF-8	alive
env -i + LANG=de_DE.UTF-8	crash
full env + LANG=de_DE.UTF-8 override	crash
LANG=de_DE + LC_NUMERIC=en_US	3/3 alive
LANG=en_US + LC_NUMERIC=de_DE	3/3 crash
LANG=de_DE + LC_NUMERIC=C	alive
open --env LC_NUMERIC=en_US.UTF-8 -a cmux (activating launch)	alive

Within this matrix LC_NUMERIC is the controlling variable: a comma-decimal numeric locale crashes the CoreUI vector-glyph rasterization during first layout (both stack manifestations — +[NSApplication _crashOnException:] via makeKeyAndOrderFront, and _os_unfair_lock_recursive_abort in -[CUINamedVectorGlyph _performWithLockedRenditions:] via the SwiftUI render path). This retroactively explains every launch-path pattern in this thread: icon launches (no LANG in the GUI session → German system locale) crashed deterministically, terminal launches depended on the shell's LANG, and the activation/emulator correlations were epiphenomena of how LANG is distributed across launch paths.

Since the throwing frames are Apple's (-[CUINamedVectorGlyph _rasterizeImageUsingScaleFactor:…]), this looks like a macOS 27 beta bug that cmux happens to trip — plausibly locale-sensitive numeric parsing in SF-Symbol/vector-glyph handling. Suggested handling:

1. App-side hardening: pin the numeric locale very early (e.g. setenv("LC_NUMERIC", "C", 1) before AppKit/SwiftUI bootstrap) so users with comma-decimal locales on the beta are safe regardless of launch path.
2. File a Feedback/radar against CoreUI with the repro above — affected population is anyone with a comma-decimal locale (de, fr, it, es, pt, nl, tr, ru, …) once macOS 27 ships.

Happy to test candidate builds. Full .ips files available on request (same policy as before). User-facing workarounds are in #7881 (body rewritten accordingly).