rtk wc does not read stdin — silent false zero on redirect and pipe

Description

rtk wc does not read stdin at all — neither via redirect (<) nor pipe (|). When no file operand is given, it prints 0 and exits 0, making it indistinguishable from a real empty file.

This is the same class as #4084 (rtk curl drops stdin body), but worse: wc is a counting instrument, and 0 is a fully plausible answer to nearly every question it gets pointed at. A false zero from wc reads as "nothing there", not as an error.

Reproduction

Each command must be alone and first in its block (see "position-dependent" note below):

# Setup
printf 'a\nb\nc\n' > /tmp/wc-test.txt

# BUG: redirect stdin — should be 3, returns 0
rtk wc -l < /tmp/wc-test.txt
# Output: 0 (rc=0)

# BUG: pipe stdin — should be 3, returns 0
printf 'a\nb\nc\n' | rtk wc -l
# Output: 0 (rc=0)

# CORRECT: file argument
rtk wc -l /tmp/wc-test.txt
# Output: 3 (rc=0)

# CORRECT: native wc
/usr/bin/wc -l < /tmp/wc-test.txt
# Output: 3 (rc=0)

Position-dependent trigger (why it looks intermittent)

rtk rewrite rewrites only the first matched command in a block. So:

• wc -l < f alone → rewritten → 0 (wrong)
• wc -l f; wc -l < f → first wc absorbs the rewrite → second runs native → 75 (correct)

This means a "characterization re-run" that adds the suspect command to an existing block will defeat reproduction. The command must be isolated.

Environment

• rtk 0.38.0
• Linux 6.6.87.2 (WSL2), x86-64

Expected behavior

Either:

1. rtk wc should forward stdin to native wc when no file arguments are given, OR
2. rtk wc should exit non-zero when stdin would be needed but isn't handled

Never: print 0 with rc=0.

Workaround

We guard this in our hook (rtk-rewrite.sh) by matching on $REWRITTEN to skip rewriting standalone wc commands while preserving pipeline upstream savings (e.g., rtk ls | wc -l still works because only ls is rewritten).

Start by reproducing the isolated redirect and pipe cases with rtk wc -l, then trace how rtk rewrite handles the first matched command and how wc handles missing file operands. Done means stdin is forwarded to native wc when no file arguments are supplied, or the command exits non-zero instead of silently printing 0; preserve the working file-operand and pipeline behavior.