fix(ls): keep the child's order when a sort key is given

[houtinghang]

Summary

rtk ls -t, -lt and -S list every directory before every file, so the first line is no longer the newest (or largest) entry (#4302). compact_ls always split the child's output into a dirs list and a files list and printed them in that order, whatever the user had asked ls to sort by. An agent that runs ls -t | head -1 to find the newest file gets a directory or an older file, and the Claude Code hook rewrites ls -lt into rtk ls -lt, so the agent never chose to run the rewritten command.

• Remember whether each entry is a directory while reading the child's output, and only partition directories to the front when no sort key was given.
• With -t, -S, -U, -X, -v, -f or GNU --sort=WORD (abbreviations resolved through the existing grammar, so --sor time counts), the child already ordered both kinds together and that order is kept as-is. On BSD only -t, -S and -f are sort keys (-U picks the timestamp -t sorts by; -v and -X mean something else), so the grouping stays there.
• Plain -l, -a and -r behave exactly as before: directories first, then files.
• The display cap now trims the tail of the sorted order instead of the tail of the files, so the newest entries survive truncation.
• Not covered: -c / -u / --time=WORD without -l or -t, which GNU ls sorts by on its own. RTK always hands the child -l, which makes GNU sort by name again, so those need a different change (forwarding --sort=time) and are left alone here.

Tests: test_plan_sort_key_keeps_child_order pins which flags count as a sort key on GNU and BSD, test_compact_sorted_keeps_child_order / test_compact_unsorted_groups_dirs_first use the issue's ls -lt output with and without a sort key (short and long rendering), and test_compact_sorted_truncates_from_the_tail checks the cap keeps the head of the sorted order. The existing compact_ls tests pass sorted = false and are otherwise unchanged.

Closes #4302

Tests

• cargo fmt --all --check
• cargo clippy --all-targets (no warnings)
• cargo test (full suite: 4001 unit tests pass). One integration test, unwritable_hooks_dir_never_breaks_the_hook, fails in my WSL environment with and without this change because the tests run as root there and root ignores the chmod the test relies on; unrelated to this PR.
• End-to-end with the issue's reproducer (touch -t timestamps plus big.bin) through the built binary, develop vs. this branch:

$ ls -t                      $ rtk ls -t (develop)     $ rtk ls -t (this PR)
new.txt                      zdir/                     new.txt  0B
old.txt                      adir/                     old.txt  0B
big.bin                      new.txt  0B               big.bin  4.9K
zdir                         old.txt  0B               zdir/
adir                         big.bin  4.9K             adir/

$ ls -S                      $ rtk ls -S (develop)     $ rtk ls -S (this PR)
big.bin                      zdir/                     big.bin  4.9K
zdir                         adir/                     zdir/
adir                         big.bin  4.9K             adir/
new.txt                      new.txt  0B               new.txt  0B
old.txt                      old.txt  0B               old.txt  0B

rtk ls -lt matches the same order with the octal column; rtk ls, rtk ls -l and rtk ls -r print the same output as develop.

AI disclosure

Written with the help of Claude (Anthropic); I reviewed the change and the test results above before opening this PR.

🤖 Generated with Claude Code

[rtk-wshm-sync-bot]

wshm · Automated triage by AI

📊 Automated PR Analysis

🐛 Type	bug-fix
🟢 Risk	low

Summary

Fixes rtk ls so that when a sort key like -t or -S is passed, entries keep the child ls process's sort order instead of always grouping directories before files. Adds a sorted flag threaded through LsPlan and compact_ls, detects sort-key flags across GNU/BSD flavors, and adjusts truncation to trim from the tail of the sorted order rather than the tail of the files list.

Review Checklist

• Tests present
• Breaking change
• Docs updated

Linked issues: #4302

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Analyzed automatically by wshm · This is an automated analysis, not a human review.