[Bug] Claude Code 2.1.243 crashes with SIGSEGV on startup (null pointer dereference)

Bug Description
Title: 2.1.243 segfaults on startup (null deref at fixed address) on Linux x86_64; 2.1.241 fine

SUMMARY
Claude Code 2.1.243 crashes with SIGSEGV immediately on launch, before any UI
appears. Every invocation fails, including claude --version, from any working
directory. Rolling the version symlink back to 2.1.241 fixes it completely.
This looks like a bad release build rather than a machine-specific problem:
2.1.239, 2.1.240 and 2.1.241 are all installed on this machine and all start
normally.

REPRODUCTION

1. Be on 2.1.243 (installed by auto-update on 2026-08-24 18:45; the launcher

symlink was repointed to it at 19:01).

1. Run claude -- or even claude --version -- from any directory.
2. Process dies immediately:

fish: Job 1, 'claude' terminated by signal SIGSEGV (Address boundary error)
Exit code 139.

100% reproducible. Shell-independent (reproduced from fish and from a
non-interactive bash invocation).

VERSION COMPARISON (same machine, same user, run back to back)
<versions-dir>/2.1.239 --version -> exit 0, "2.1.239 (Claude Code)"
<versions-dir>/2.1.240 --version -> exit 0, "2.1.240 (Claude Code)"
<versions-dir>/2.1.241 --version -> exit 0, "2.1.241 (Claude Code)"
<versions-dir>/2.1.243 --version -> exit 139 (SIGSEGV)

(<versions-dir> is the native installer's per-user versions directory, the
default location; all four binaries sit side by side there.)

Working directory is irrelevant -- 2.1.243 was tried from the home directory,
from a local filesystem and from an NFS mount, and segfaults identically in
every case.

KERNEL LOG (three separate launches)
claude[163831]: segfault at 0 ip 0000000001d10458 sp 00007ffc29d05900 error 4 in 2.1.243[1b0f458,1953000+3b33000] likely on CPU 2
claude[163952]: segfault at 0 ip 0000000001d10458 sp 00007ffc7b80ed90 error 4 in 2.1.243[1b0f458,1953000+3b33000] likely on CPU 3
claude[163968]: segfault at 0 ip 0000000001d10458 sp 00007ffc512e7960 error 4 in 2.1.243[1b0f458,1953000+3b33000] likely on CPU 3

Notable: identical faulting instruction pointer (0x1d10458, module offset
0x1b0f458) every time, "segfault at 0" with error code 4 -- a user-mode read of
a null pointer. Deterministic null dereference during startup, not memory
corruption or a race.

POSSIBLY RELEVANT
The 2.1.243 binary is substantially larger than its predecessors, so this
release seems to carry a real build change rather than a patch:
342563120 2.1.239
342636848 2.1.240
342636848 2.1.241
377568472 2.1.243
ldd on the 2.1.243 binary reports no missing shared libraries.

Note on one theory worth ruling out: this machine runs CachyOS, which ships
aggressively optimized builds, so an instruction-set baseline mismatch is a
natural suspicion. It does not fit the evidence -- a too-new instruction
baseline raises SIGILL, not a null-pointer read at a fixed address.

ENVIRONMENT
OS: CachyOS (Arch-based)
Kernel: 7.2.0-1-cachyos, x86_64
glibc: 2.44
CPU: Intel Core i7-7700HQ (Kaby Lake; AVX2, no AVX-512)
Node: v26.7.0 (likely irrelevant -- the installed binary is a native ELF
executable, not a node script)
Install: native installer (per-user versions directory, symlinked onto PATH)
Terminal: xterm-256color

WORKAROUND
Repoint the launcher symlink at the last known-good version:
ln -sfn <versions-dir>/2.1.241 <bin-dir>/claude
Confirmed working. Note that an already-running session survives the bad
update, since it keeps executing the older binary from memory -- which masks
the problem until the next launch.

Environment Info

• Platform: linux
• Terminal: konsole
• Version: 2.1.241
• Feedback ID: 77d002ba-64af-4e69-a9de-94f6bde16cac

Errors

[]

Stack trace of thread 34666:
#0  0x0000000001d10458 free (2.1.243 + 0x1b10458)
#1  0x00007ff08163a1ab __newlocale (libc.so.6 + 0x3a1ab)
#2  0x0000000001abd282 n/a (2.1.243 + 0x18bd282)
#3  0x00007ff0816b2584 n/a (libc.so.6 + 0xb2584)
#4  0x00007ff0816b26a9 pthread_once (libc.so.6 + 0xb26a9)
#5  0x0000000001abc2d2 n/a (2.1.243 + 0x18bc2d2)

#!/bin/sh
PIN="${CLAUDE_PIN:-2.1.241}"
BIN="$HOME/.local/share/claude/versions/$PIN"
if [ ! -x "$BIN" ]; then
  echo "claude: pinned version $PIN not found in ~/.local/share/claude/versions" >&2
  exit 127
fi
exec "$BIN" "$@"