[BUG] Memory spikes during high tool fan-out in Explore mode on macOS (2.1.68)

Preflight Checklist

• [x] I searched existing issues and did not find this exact case (related but different: #20369)
• [x] This is a single bug report
• [x] I am using the latest Claude Code

What's Wrong?

When Claude Code does a broad Explore pass and triggers a high number of tool calls in one turn (roughly 30+), memory usage spikes very quickly and my Mac becomes sluggish or freezes.

I can reproduce this on the latest version (2.1.68).

Important detail: I already mitigated orphan Node processes with an external cleaner and launchd job. Even with orphan cleanup in place, high fan-out tool exploration still causes severe memory pressure episodes.

What Should Happen?

Memory should stay bounded during heavy exploration. If tool fan-out is high, the CLI should backpressure/schedule safely instead of causing system-level memory pressure.

Error Messages / Logs

No single fatal stack trace. The symptom is system memory pressure + swap growth.

Incident snapshots from this machine:

# During spike (2026-03-04)
memory_pressure -Q
System-wide memory free percentage: 39%

sysctl vm.swapusage
vm.swapusage: total = 29696.00M  used = 28610.44M  free = 1085.56M

vm_stat (excerpt)
Pages stored in compressor: 2157303
Swapouts: 10086565

# Another spike window
memory_pressure -Q
System-wide memory free percentage: 30%

vm_stat (excerpt)
Swapouts: 16568459
Pageouts: 511201

# Current environment check (after recovery)
claude --version
2.1.68 (Claude Code)

memory_pressure -Q
System-wide memory free percentage: 51%

sysctl vm.swapusage
vm.swapusage: total = 4096.00M  used = 3311.62M  free = 784.38M

Steps to Reproduce

1. Start a fresh Claude Code session in a medium/large repo.
2. Ask Claude to broadly explore architecture and related files (cross-folder, dependency tracing).
3. Observe tool activity in that turn; in my case it often fans out to many calls (roughly 30+).
4. Keep the session running while tool calls return.
5. Memory pressure rises sharply and swap grows fast; terminal can become unresponsive.

Claude Model

Sonnet (default)

Is this a regression?

I don't know.

Last Working Version

Not sure. (I did not see this severity in an older npm-distributed setup, but I don't have an exact version number.)

Claude Code Version

2.1.68 (Claude Code)

Platform

Anthropic API / Claude subscription login (not Bedrock/Vertex)

Operating System

macOS (arm64)

• macOS 26.3 (Build 25D125)
• Hardware memory: 19327352832 bytes (sysctl -n hw.memsize)

Terminal / Shell

• Ghostty (main)
• Also reproduced when using Terminal.app
• Shell: zsh

Additional Information

• Related issue: #20369 (orphaned subagent after terminal termination). My case is broader: high tool fan-out during active Explore turns, even after orphan mitigation.
• It would help a lot to have a CLI setting to cap concurrent tool calls (for example, max_parallel_tool_calls). This would provide a practical safety valve for memory-constrained machines.