[Bug] Windows binary selection picks AVX version on non-AVX CPUs #8744

Summary

The Windows launcher script (bin/opencode) picks opencode-windows-x64 instead of opencode-windows-x64-baseline on CPUs without AVX support, causing immediate crash on startup.

Environment

• OS: Windows 11
• CPU: Intel/AMD without AVX (only SSE4.2)
• opencode-ai version: 1.1.19-1.1.22 (all affected)
• Node.js: v22.x

Error

Bun v1.3.6 (d530ed99) Windows x64 (baseline)
CPU: sse42
Features: ... no_avx2 no_avx ...

CPU lacks AVX support. Please consider upgrading to a newer CPU.
panic(main thread): Illegal instruction at address 0x7FF7132980FC
oh no: Bun has crashed.

Root Cause

The launcher script in bin/opencode uses:

const base = "opencode-" + platform + "-" + arch
// ...
for (const entry of entries) {
  if (!entry.startsWith(base)) continue
  // picks first match
}

Both opencode-windows-x64 and opencode-windows-x64-baseline match the pattern opencode-windows-x64. The first match wins, which depends on filesystem ordering (directory enumeration order).

Suggested Fix

Option A: Check AVX support before selecting binary (preferred)

// Detect AVX support and prefer baseline when not available
const hasAvx = checkCpuFeature('avx');
const preferBaseline = !hasAvx;

Option B: Prefer -baseline suffix when on Windows

// Sort entries to prefer baseline on Windows
entries.sort((a, b) => {
  const aBaseline = a.includes('-baseline');
  const bBaseline = b.includes('-baseline');
  // Prefer baseline if no AVX detected
  return preferBaseline ? (bBaseline - aBaseline) : (aBaseline - bBaseline);
});

Option C: Document OPENCODE_BIN_PATH workaround prominently

Workaround

Users can set the OPENCODE_BIN_PATH environment variable to force the baseline binary:

[System.Environment]::SetEnvironmentVariable(
  'OPENCODE_BIN_PATH',
  'C:\Users\<USERNAME>\AppData\Roaming\npm\node_modules\opencode-ai\node_modules\opencode-windows-x64-baseline\bin\opencode.exe',
  'User'
)

Impact

This affects all Windows users with older CPUs that lack AVX support (pre-2011 Intel, pre-2012 AMD). The crash occurs immediately on startup before any meaningful error message can be displayed, making it difficult to diagnose.

References

• Related Bun issue: The crash is in Bun runtime, but the binary selection logic is in OpenCode
• Discovered via oh-my-opencode fork: https://github.com/sadnow/oh-my-opencode