feat(builtins): stream grep and tr through pipelines

[chaliy]

Requested by Михайло · project thread

What changed

grep and tr now stream when they are a pipeline stage, following plain cat (#2584). They read input in ~4 KiB pieces and write results as they go. grep cuts its pieces on record ends and tr on UTF-8 character ends. grep -m stops reading once its budget is spent. Options that need the whole input stay buffered and drain the pipe first:

• grep -c/-l/-L/-q, context lines, -b, -r
• tr -s

The shared piece reader (InputChunks) lives in builtins/mod.rs so more filters can adopt it.

Why

This is roadmap step 2 (concurrent/streaming execution). producer | grep pat | head is one of the most common agent pipelines. Before this change, a grep or tr stage downstream of an endless or large producer read everything, so it ran until a limit fired instead of stopping at SIGPIPE.

Before / After

Script	Before	After (= bash)
while :; do echo y; done | grep y | head -2	runs until a limit	y y, PIPESTATUS 141 141 0
yes | tr y n | head -1	runs until a limit	n, 141 141 0
yes | tr -d '\n' | head -c 5	runs until a limit	yyyyy, 141 141 0
grep . big | head -1; echo ${PIPESTATUS[*]}	0 0	141 0
yes | grep -o -m3 y | cat	runs until a limit	3 lines, 141 0 0

Proof: l_pipe_001_grep_tr_stream and l_pipe_001_buffered_filter_options_drain_pipe (bash-verified). I also ran a differential script over grep -c/-v/-n/-i/-H/-z/-a, multiple files, a missing file, binary input and the tr variants. Its only differences are existing ones outside streaming: stderr ordering, byte-wise tr 'é' e, and \r stripping.

Risk

Medium-low. The buffered paths are unchanged apart from draining a streaming pipe. tr's logic moved into TrSpec::apply unchanged. Binary input in a stream is reported once with binary file matches from the point the NUL is seen.

Checklist

• Failing test first
• cargo test -p bashkit --lib / --test integration / bash_comparison
• clippy -D warnings, fmt, check-okf, check-doc-links
• knowledge: parallel-execution, limitations L-PIPE-001, log

https://claude.ai/code/session_019aFikmptPc91Fj4N2iDXQA

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