fix(completion): scope completion to the current simple command

[reubeno]

COMP_WORDS/COMP_LINE/COMP_CWORD and the command-name lookup covered the whole input line, so echo foo; X=1 cmd <Tab> looked up completions for echo. Like bash, start after the last command separator and skip leading variable assignments.

Assisted-By: Claude Fable 5.1 noreply@anthropic.com

[github-actions]

Test Results

    5 files     49 suites   21m 28s ⏱️
2 950 tests 2 950 ✅ 0 💤 0 ❌
9 149 runs  9 149 ✅ 0 💤 0 ❌

Results for commit b9ae138.

♻️ This comment has been updated with latest results.

[github-actions]

Performance Benchmark Report

Benchmark name	Baseline (μs)	Test/PR (μs)	Delta (μs)	Delta %
clone_shell_object	13.18 μs	13.62 μs	0.45 μs	🟠 +3.39%
eval_arithmetic	0.11 μs	0.11 μs	-0.00 μs	⚪ Unchanged
expand_one_string	1.22 μs	1.22 μs	0.00 μs	⚪ Unchanged
for_loop	20.12 μs	20.22 μs	0.10 μs	⚪ Unchanged
full_peg_complex	40.37 μs	40.36 μs	-0.01 μs	⚪ Unchanged
full_peg_for_loop	4.48 μs	4.46 μs	-0.02 μs	⚪ Unchanged
full_peg_nested_expansions	11.64 μs	11.64 μs	0.00 μs	⚪ Unchanged
full_peg_pipeline	3.00 μs	3.01 μs	0.01 μs	⚪ Unchanged
full_peg_simple	1.21 μs	1.22 μs	0.01 μs	⚪ Unchanged
function_call	2.51 μs	2.53 μs	0.02 μs	⚪ Unchanged
instantiate_shell	39.45 μs	39.87 μs	0.42 μs	⚪ Unchanged
instantiate_shell_with_init_scripts	18609.65 μs	18834.82 μs	225.17 μs	⚪ Unchanged
parse_peg_bash_completion	1604.04 μs	1588.62 μs	-15.41 μs	⚪ Unchanged
parse_peg_complex	12.60 μs	12.51 μs	-0.08 μs	⚪ Unchanged
parse_peg_for_loop	1.29 μs	1.26 μs	-0.04 μs	⚪ Unchanged
parse_peg_pipeline	1.44 μs	1.43 μs	-0.01 μs	⚪ Unchanged
parse_peg_simple	0.73 μs	0.74 μs	0.00 μs	⚪ Unchanged
run_echo_builtin_command	8.83 μs	8.86 μs	0.04 μs	⚪ Unchanged
tokenize_sample_script	2.50 μs	2.56 μs	0.06 μs	⚪ Unchanged

Code Coverage Report: Only Changed Files listed

Package	Base Coverage	New Coverage	Difference
brush-core/src/completion.rs	🟠 74.32%	🟢 76.81%	🟢 2.49%
brush-core/src/extendedtests.rs	🟠 75%	🟢 75.76%	🟢 0.76%
brush-core/src/openfiles.rs	🟠 64.15%	🟠 64.62%	🟢 0.47%
brush-core/src/regex.rs	🟢 99.17%	🟢 100%	🟢 0.83%
brush-core/src/results.rs	🟢 80.16%	🟢 80.62%	🟢 0.46%
brush-core/src/shell.rs	🟢 94.78%	🟢 95.38%	🟢 0.6%
brush-core/src/shell/prompts.rs	🟢 97.62%	🟢 97.37%	🔴 -0.25%
brush-core/src/wellknownvars.rs	🟢 84.53%	🟢 84.72%	🟢 0.19%
brush-interactive/src/interactive_shell.rs	🟠 65.67%	🟠 68.51%	🟢 2.84%
brush-parser/src/parser/peg.rs	🟢 95.39%	🟢 95.42%	🟢 0.03%
brush-shell/src/config.rs	🟢 95.77%	🟢 95.65%	🔴 -0.12%
brush-shell/src/entry.rs	🟢 91.1%	🟢 92.74%	🟢 1.64%
xtask/src/e2e.rs	🔴 0%	🟠 57.98%	🟢 57.98%
Overall Coverage	🟢 77.54%	🟢 77.23%	🔴 -0.31%

Minimum allowed coverage is 70%, this run produced 77.23%
Maximum allowed coverage difference is -5%, this run produced -0.31%

Test Summary: bash-completion test suite

Outcome	Count	Percentage
✅ Pass	1586	75.20
❗️ Error	18	0.85
❌ Fail	151	7.16
⏩ Skip	339	16.07
❎ Expected Fail	13	0.62
✔️ Unexpected Pass	2	0.09
📊 Total	2109	100.00