Bash sandbox hardcodes /tmp, unusable on Termux/Android

On Termux (Android), /tmp is on a read-only filesystem. The Bash tool sandbox unconditionally tries to mkdir /tmp/claude-{pid} before executing any command, which fails with EACCES: permission denied. This makes every single Bash call fail, even trivial ones like echo test.

Environment

• Platform: Android (Termux)
• Kernel: Linux 6.6.x-android15
• Claude Code installed via npm in Termux
• /tmp exists but is read-only — cannot chmod, rm, or symlink over it

What happens

Every Bash tool call fails before the actual command runs:

EACCES: permission denied, mkdir '/tmp/claude-10473'

What was tried

• chmod 777 /tmp → Permission denied
• ln -sf $PREFIX/tmp /tmp → Permission denied
• rm -rf /tmp && ln -s ... → Read-only file system
• TMPDIR=$PREFIX/tmp claude → Sandbox still uses /tmp, not $TMPDIR
• Setting TMPDIR inside commands → Sandbox fails before command executes

Expected behavior

The sandbox should use os.tmpdir() or respect $TMPDIR instead of hardcoding /tmp. Termux sets $PREFIX/tmp as the writable temp directory.

Impact

All non-Bash tools (Read, Write, Edit, Glob, Grep, WebFetch, etc.) work fine. Only the Bash sandbox is affected, but this effectively disables shell access entirely on Termux.