opencode 1.18.21 crashes with SIGILL at UD2 instruction

Description

opencode 1.18.21 crashed with SIGILL while running a session.

Crash details

• Version: 1.18.21
• Command line: opencode --session ses_fb57a18d8ffe3w2WSbWSw3CR62
• Signal: SIGILL
• Signal code: ILL_ILLOPN
• Crash time: 2026-08-29 12:03:34 CDT
• Binary: /home/felix/.local/share/mise/installs/opencode/1.18.21/opencode
• Build ID: c30f169b1bef81fa57467cd091ba53aab5235468
• CPU: Intel Core i7-8665U
• OS: Arch Linux, kernel 7.1.11-arch1-1
• Architecture: x86-64

The kernel reported:

traps: opencode[15987] trap invalid opcode

The instruction at the crash address is:

0x2607064: ud2

The coredump backtrace is unsymbolized:

#0  0x0000000002607064 in ?? ()

The core contained 29 threads. Most other threads were in runtime/internal wait or worker code. The coredump also recorded two deleted temporary modules without build IDs:

/tmp/.bcd9cfdfbfadf27d-00000001.so
/tmp/.9adb4bfbeef0ef8f-00000000.so

There was no evidence of OOM: at diagnosis time the system had approximately 6.7 GiB available memory and no swap in use.

This appears to be an internal fatal path or assertion in the opencode executable, but the available symbols do not identify the triggering code path.

The crash has only been observed once so far.

Expected behavior

The opencode process should continue running or report a recoverable application error rather than terminate with SIGILL.

Additional information

The coredump is available locally through systemd-coredump, but it has not been uploaded because it may contain private prompts, tokens, and user data.

Filed by the current model via pi coding-agent harness.