test(grep): pin -n with -A/-B context line numbering + separators

[tobert]

What

Adds test_grep_line_numbers_with_context, exercising -n together with -A/-B context — a combination no existing test covered (we had -n alone and context alone).

Why

-n's interaction with context is where GNU compatibility lives: matched lines use the : separator, context lines use -, and every emitted line must be numbered. Nothing pinned that, so a regression in either the numbering or the separator logic would have passed silently.

Test

Matches two in /lines.txt (line one\nline two\nline three\nfour) with -n -B1 -A1 and asserts exact output:

1-line one
2:line two
3-line three

Exact-equality so it fails loudly on any drift.

• cargo test -p kaish-kernel --lib grep — 44 passed
• cargo clippy --all-targets — clean

🤖 Generated with Claude Code

[tobert]

kaibo review (cast: deepseek — explorer deepseek-v4-flash, synth deepseek-v4-pro)

Verdict: correct and ready to land. kaibo traced the assertion against the real rendering code rather than taking it on faith.

Question	Verdict
Expected output correct?	✅ Exact match with render_events
Exercises genuine rendering path?	✅ Hits grep_lines_structured → render_events; context flags force the whole-buffer path, skipping the streaming shortcut
Fixture + match line correct?	✅ "two" matches only line 2; lines 1 and 3 are the correct before/after context
Gaps?	-C not a gap (resolves to the same GrepOptions + code path). -- break + -n and multi-file + context + -n are possible future tests, out of scope here.

Detail

• Separators: the prefix(line_num, sep) closure (grep.rs:1013–1025) emits ':' for SearchEvent::Match (grep.rs:1055) and '-' for all ContextKind variants (grep.rs:1076–1078) — so 1-line one, 2:line two, 3-line three is exactly right.
• Path fidelity: the before-context/after-context named keys are the same canonical keys the kernel dispatcher binds; to_argv() round-trips them to --before-context=1/--after-context=1, clap parses, parse_context() resolves to Some(1). Because context is Some, the streaming shortcut (grep.rs:358–359) is skipped, so the test genuinely hits the render_events separator logic. Consistent with the existing direct-execute() convention used by all grep tests.

Suggested follow-ups (not blocking, deferred)

• multi-file + context + -n (filename prefix interacting with line-number prefix: file.txt:2:line two for matches, file.txt-1-line one for context)
• -- context-break separator with -n on non-contiguous matches

🤖 Generated with Claude Code