Loop variables become empty when piped to another command

Bug Description

When using shell loop variables inside a pipe, the variable value becomes empty. This happens only when there's a pipe inside the loop body.

Reproduction Steps

1. Run a simple loop without a pipe - works correctly:

for i in a b c; do echo "val=$i"; done

Output: val=a, val=b, val=c ✓

1. Run the same loop with a pipe - variable becomes empty:

for i in a b c; do echo "val=$i" | cat; done

Output: val=, val=, val= ✗

Expected Behavior

The loop variable $i should retain its value when used in a pipeline.

Actual Behavior

The loop variable $i becomes empty when the command is piped to another command.

Impact

This breaks common shell patterns like:

for i in 1 2 3; do echo "mark $i yellow" | nc -N 127.0.0.1 9876; done

Which results in mark yellow being sent (missing the number).

Workaround

Using explicit bash invocation works:

/bin/bash -c 'for i in a b c; do echo "val=$i" | cat; done'

Environment

• Shell: zsh
• Platform: Linux (Arch)
• The issue appears to be in Claude Code's command preprocessing before passing to the shell.

Analysis

The error message shows (eval):1: which suggests Claude Code is using eval to execute commands. The variable substitution appears to happen incorrectly during this evaluation phase when pipes are involved.