Bash tool: all commands return exit code 1 after sandbox process crash

Bug Description

All Bash tool invocations fail with Error: Exit code 1 after the internal sandbox shell subprocess crashes mid-session. This affects every command, including trivially infallible ones like true, echo "test", and pwd. The failure persists for the remainder of the session; only starting a new session recovers.

Reproduction

Not reliably reproducible on demand, but observed repeatedly during sessions with heavy parallel usage (multiple concurrent Claude Code sessions + subagents in the same repo). When it triggers:

⏺ Bash(echo "test")
  ⎿  Error: Exit code 1

⏺ Bash(true)
  ⎿  Error: Exit code 1

⏺ Bash(pwd)
  ⎿  Error: Exit code 1

Every Bash call fails identically. Non-Bash tools (Read, Glob, Grep, Edit) continue working normally.

Environment

• OS: macOS (Darwin 25.3.0)
• Shell: zsh
• Claude Code model: claude-opus-4-6
• Hooks configured: PreToolUse (session-guard on git/Edit/Write matchers), PostToolUse (async telemetry), Stop, SubagentStop
• Concurrent sessions at time of failure: 4+ Claude processes (main session + subagents across multiple git worktrees)

Analysis

• The hooks are not the cause — PreToolUse matchers are scoped to specific patterns (Bash(git add*), Edit, Write, etc.) and do not match generic Bash(echo *) or Bash(true).
• The exit code 1 is coming from the tool execution layer itself, not from the commands being run (since true cannot exit non-zero).
• Starting a new session immediately resolves the issue, confirming the sandbox subprocess died rather than a systemic OS/shell problem.
• Likely trigger: resource exhaustion (pty allocation, process tree depth, or internal sandbox state) under heavy parallel load.

Expected Behavior

Bash tool should either:

1. Automatically detect and restart a dead sandbox subprocess, or
2. Surface a clear error message ("Sandbox process died, please restart session") instead of misleading Exit code 1 on every command.

Workaround

Restart the Claude Code session. The new session gets a fresh sandbox and commands work immediately.