[BUG] macOS kills 3rd+ concurrent Claude Code instance with SIGKILL (Taskgated Invalid Signature)

Description

When running 2 concurrent Claude Code CLI sessions on macOS, attempting to launch a 3rd instance results in immediate SIGKILL — the process is killed before any output is displayed. The macOS crash report confirms the cause is code signature validation failure by taskgated, not an OOM condition.

Environment

• macOS 26.3 (Build 25D125) — Apple Silicon
• Mac model: Mac16,10
• Claude Code: 2.1.59
• RAM: 24 GB (free ~86% at time of crash)
• Shell: zsh

Steps to Reproduce

1. Open Terminal 1, run claude → starts normally
2. Open Terminal 2, run claude → starts normally
3. Open Terminal 3, run claude → immediately killed

Output in Terminal 3:

zsh: killed     claude

Even claude --version is killed when 2 sessions are already running:

$ claude --version
$ echo $?
137

Crash Report Evidence

macOS generates crash reports at ~/Library/Logs/DiagnosticReports/2.1.59-*.ips (26 reports accumulated in one day).

Key fields from the crash report:

{
  "exception": {
    "type": "EXC_CRASH",
    "signal": "SIGKILL (Code Signature Invalid)"
  },
  "termination": {
    "flags": 66,
    "code": 1,
    "namespace": "CODESIGNING",
    "indicator": "Taskgated Invalid Signature"
  }
}

Analysis

• Not a memory issue: memory_pressure reports 86% free, node -e "Buffer.alloc(500*1024*1024)" succeeds, and no Jetsam logs are found
• Code signature appears valid: codesign -vv returns "valid on disk" and "satisfies its Designated Requirement", signed by "Developer ID Application: Anthropic PBC (Q6L2SF6YDW)"
• Gatekeeper rejects it: spctl --assess --type execute returns "rejected (the code is valid but does not seem to be an app)"
• Binary has com.apple.provenance xattr that cannot be removed
• CLAUDE_DEBUG=1 claude --version succeeds (exit 0), while without the env var it fails (exit 137) — suggesting a timing or initialization path difference affects the signature validation

Codesign Details

Identifier=com.anthropic.claude-code
Format=Mach-O thin (arm64)
CodeDirectory v=20500 size=1450661 flags=0x10000(runtime) hashes=45322+7
Authority=Developer ID Application: Anthropic PBC (Q6L2SF6YDW)
Authority=Developer ID Certification Authority
Authority=Apple Root CA
Timestamp=Feb 26, 2026 at 8:52:45
TeamIdentifier=Q6L2SF6YDW
Runtime Version=14.5.0

Impact

This limits concurrent Claude Code sessions to 2 on macOS, making parallel workflows (e.g., 2 PR reviews + 1 development session) impossible.

Potentially Related Issues

• #19019 — Crash when running multiple instances with custom statusLine
• #19068 — PAC crash on startup (macOS 26.2)
• #14911 — Gatekeeper warning for extracted .node native addon
• #28860 — MCP server process sharing (my earlier feature request about memory)