Sed branch loop limit silently truncates output without warning

[chaliy]

Summary

The sed branch/label execution loop has a limit of 1000 iterations per line. When exceeded, execution silently stops without error or warning. Legitimate sed scripts using branches (counters, complex transformations) produce incorrect output silently — a data integrity issue.

Severity: Low
Category: Silent Data Corruption / Correctness

Affected Files

• crates/bashkit/src/builtins/sed.rs lines 823-826

Steps to Reproduce

# Legitimate sed loop needing >1000 iterations
printf 'a' | sed ':loop; s/a/aa/; /.\{2000\}/!b loop'
# Silently stops at 1000 iterations, producing wrong output length

Impact

Silent data corruption. Scripts depending on sed loops produce incorrect results without any warning.

Acceptance Criteria

• Emit stderr warning when branch iteration limit is hit
• Or: make the limit configurable
• Test: Hitting the limit produces a warning on stderr
• Test: Normal sed scripts under 1000 iterations work unchanged