feat: auto-update parent directory mtime on content changes (#186)

[Koan-Bot]

Summary

Fixes #186. When files or directories are created or removed inside a mocked directory, the parent directory's mtime and ctime are now automatically updated to match real Linux filesystem behavior.

What changed

Added _update_parent_dir_times($path) helper that finds the mocked parent directory and bumps its mtime/ctime to time().

Instrumented these operations:

• file() constructor — when file has defined contents
• symlink() constructor — when symlink has defined target
• unlink() method — when file/symlink is removed
• __open() — when opening for write creates a new file (contents was previously undef)
• __sysopen() — with O_CREAT on non-existent file
• __mkdir() / __rmdir() — directory creation/removal

What didn't change

• Writing to an existing file does not update parent dir mtime (matches real FS)
• Files created with undef contents (nonexistent mocks) don't update parent mtime
• No crash when parent directory isn't mocked

Test coverage

New test file t/dir_mtime.t with 10 subtests covering all instrumented operations, edge cases (no parent mock, existing file writes), and ctime co-update.

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🤖 Generated with Claude Code

[atoomic]

Failure from CI

    # Failed test 'directory has mtime'
    # at t/dir_mtime.t line 21.
    # Failed test 'Unexpected warning: Use of uninitialized value $dir_mtime_before in numeric gt (>) at t/dir_mtime.t line 27.'
    # [No trace info available]

# Failed test 'file creation updates parent dir mtime'
# at t/dir_mtime.t line 28.
    # Failed test 'Unexpected warning: Use of uninitialized value $parent_mtime_before in numeric gt (>) at t/dir_mtime.t line 73.'
    # [No trace info available]
    # Failed test 'Unexpected warning: Use of uninitialized value $parent_mtime_after in numeric gt (>) at t/dir_mtime.t line 73.'
    # [No trace info available]
    # Failed test 'parent dir mtime updated after mkdir'
    # at t/dir_mtime.t line 73.

# Failed test 'mkdir updates parent dir mtime'
# at t/dir_mtime.t line 75.
    # Failed test 'Unexpected warning: Use of uninitialized value $parent_mtime_before in numeric gt (>) at t/dir_mtime.t line 89.'
    # [No trace info available]
    # Failed test 'Unexpected warning: Use of uninitialized value $parent_mtime_after in numeric gt (>) at t/dir_mtime.t line 89.'
    # [No trace info available]
    # Failed test 'parent dir mtime updated after rmdir'
    # at t/dir_mtime.t line 89.

# Failed test 'rmdir updates parent dir mtime'
# at t/dir_mtime.t line 91.
    # Failed test 'Unexpected warning: Use of uninitialized value $dir_mtime_before in numeric gt (>) at t/dir_mtime.t line 108.'
    # [No trace info available]
    # Failed test 'Unexpected warning: Use of uninitialized value $dir_mtime_after in numeric gt (>) at t/dir_mtime.t line 108.'
    # [No trace info available]
    # Failed test 'dir mtime updated when open creates new file'
    # at t/dir_mtime.t line 108.

# Failed test 'open for write creates file and updates parent dir mtime'
# at t/dir_mtime.t line 110.
    # Failed test 'directory has ctime'
    # at t/dir_mtime.t line 150.
    # Failed test 'Unexpected warning: Use of uninitialized value $dir_ctime_before in numeric gt (>) at t/dir_mtime.t line 156.'
    # [No trace info available]

# Failed test 'ctime also updates alongside mtime'
# at t/dir_mtime.t line 157.
# Seeded srand with seed '20260222' from local date.
t/dir_mtime.t ....................... 

[atoomic]

@Koan-Bot rebase

[Koan-Bot]

The new_dir() fix (8c996cb) is already on this branch and addresses all the reported test failures. The tests were using dir() which creates a non-existent placeholder — stat returns empty for those. Changed to new_dir() which calls __mkdir internally, so directories exist immediately with proper stat values.

Branch is up to date with master (7d115e8). The CI failure was from before the fix was pushed — needs a fresh CI run.