fix(core): avoid deadlock on here-documents larger than the pipe buffer

[cataggar]

Overview

Fix a deadlock when a here-document or here-string is larger than the pipe buffer.

This change was made by GitHub Copilot at my direction.

Details

setup_open_file_with_contents currently writes the complete payload into an anonymous pipe before the command that reads from it has been spawned. The write blocks indefinitely when the payload exceeds the available pipe capacity. This is especially visible on Windows, where the default pipe buffer is 4 KiB.

This change:

• keeps direct writes for payloads up to 4 KiB;
• retains Linux and Android pipe resizing as a best-effort fast path;
• falls back to a named writer thread when the payload cannot safely fit;
• avoids failing redirection when F_SETPIPE_SZ rejects an empty payload or one above the system pipe-size limit; and
• adds bash-oracle compatibility cases for large here-documents and here-strings.

The helper thread exits after the reader consumes the payload, or earlier on a broken pipe if the command closes the read end without consuming it.

Testing

• cargo test --test brush-compat-tests -- here
• cargo xtask check fmt
• cargo clippy --package brush-core --package brush-shell --all-features --all-targets

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	17.42 μs	17.40 μs	-0.02 μs	⚪ Unchanged
eval_arithmetic	0.15 μs	0.15 μs	0.00 μs	⚪ Unchanged
expand_one_string	1.60 μs	1.73 μs	0.13 μs	🟠 +8.26%
for_loop	31.05 μs	31.09 μs	0.04 μs	⚪ Unchanged
full_peg_complex	59.88 μs	58.58 μs	-1.30 μs	🟢 -2.17%
full_peg_for_loop	6.42 μs	6.23 μs	-0.19 μs	🟢 -2.96%
full_peg_nested_expansions	16.42 μs	16.36 μs	-0.06 μs	⚪ Unchanged
full_peg_pipeline	4.53 μs	4.38 μs	-0.15 μs	🟢 -3.38%
full_peg_simple	1.92 μs	1.86 μs	-0.06 μs	🟢 -3.03%
function_call	3.34 μs	3.35 μs	0.01 μs	⚪ Unchanged
instantiate_shell	53.76 μs	54.18 μs	0.42 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	25963.56 μs	26866.98 μs	903.42 μs	🟠 +3.48%
parse_peg_bash_completion	2137.46 μs	2120.36 μs	-17.10 μs	🟢 -0.80%
parse_peg_complex	21.86 μs	21.42 μs	-0.44 μs	⚪ Unchanged
parse_peg_for_loop	2.16 μs	2.08 μs	-0.08 μs	🟢 -3.66%
parse_peg_pipeline	2.31 μs	2.32 μs	0.01 μs	⚪ Unchanged
parse_peg_simple	1.22 μs	1.17 μs	-0.04 μs	🟢 -3.45%
run_echo_builtin_command	16.40 μs	16.12 μs	-0.28 μs	⚪ Unchanged
tokenize_sample_script	3.46 μs	3.42 μs	-0.04 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
Overall Coverage	🟢 27.49%	🟢 27.48%	🔴 -0.01%

Minimum allowed coverage is 20%, this run produced 27.48%
Maximum allowed coverage difference is -5%, this run produced -0.01%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1583	75.06
❗️ Error	17	0.81
❌ Fail	155	7.35
⏩ Skip	339	16.07
❎ Expected Fail	13	0.62
✔️ Unexpected Pass	2	0.09
📊 Total	2109	100.00