Bun crashes with "Illegal instruction" during long sessions with context compression on Windows 11

Environment

• Claude Code v2.1.81, Bun v1.3.11
• Windows 11 Pro 10.0.22000, x64 (SSE4.2 + AVX2)
• CPU baseline features only (no AVX-512)
• Model: claude-opus-4-6 (1M context)

Description

Multiple Bun crashes during a single long session (~5 hours). The crashes occur specifically when context compression fires and Claude Code is rebuilding/propagating context -- not during normal tool use or computation.

This is notable because the same machine regularly runs calculation-heavy sessions (multi-agent parallel searches, 824-session backtests, large file reads, dozens of sequential tool calls) without any crashes. The differentiator appears to be context compression cycles, not computational load.

Crash details

Bun v1.3.11 (a2743b6d) Windows x64 (baseline)
RSS: 1.69GB | Peak: 1.69GB | Commit: 4.94GB | Faults: 17723313
panic(main thread): Illegal instruction at address 0x7FF6382FD19A

Crash report: bun.report/1.3.11/e_1a2743b6mgkgEuhogC05onlDo2q01Dqt9gvDgt6slDi+6slD+xts4C6v+o4Cm/4o4Cmx4o4C2ilt6B657j5Bwt1p4By/yj5Bylyj5Bwg2rvB+5zl/B____A3s//B05o/l4B

Reproduction pattern

1. Long conversation (4-5+ hours continuous use)
2. Heavy tool use throughout (parallel agents, file reads, edits, bash commands)
3. Context approaches compression threshold
4. Crash occurs during or immediately after compression ("Propagating..." / "Churning..." status)
5. Session restarts cleanly, same work resumes without issues until next compression cycle

Multiple crashes in the same session, all at the compression boundary. Never crashes during normal tool execution regardless of complexity.

What doesn't cause it

• Parallel agent spawning (5+ concurrent agents)
• Large file reads (100KB+ files)
• Heavy bash execution (5+ minute Python runs)
• Sequential tool chains (30+ tool calls in sequence)
• Any of the above at normal context lengths