Nice work, @Chaosuk97 — this is a well-structured improvement that addresses a real usability pain point. The behaviour matrix in the PR description is appreciated; it's clear you've thought through the edge cases. A few observations:

Looks good

• The retry-with-backoff in AdifParser::parseFileAsync is sensible for the write-lock scenario and correctly runs on the worker thread (no GUI stall). The openFailed signal is a clean way to preserve existing worked status on failure.
• Moving watcher re-registration from fileChanged into the debounce timeout callback is the right fix for atomic-rename exports — by the time the 2s window expires, the replacement file is present and the new inode gets tracked.
• Directory watcher for delete→recreate is a good addition. The guard (QFileInfo::exists + !m_fileWatcher.files().contains) keeps it cheap even in busy directories.
• The removal of the toggle simplifies both the code and the UX. Always-on watching after a Browse selection is the right default.

Minor items to consider (non-blocking)

1. Directory watcher noise in busy folders: If the user's ADIF file lives in a directory with heavy write traffic (e.g. a logging program's working directory with temp files), directoryChanged will fire for every unrelated file event. The current guard is lightweight (exists + contains check), so this is fine in practice, but worth noting in case users report CPU spikes on certain setups. A future optimisation could compare QFileInfo::lastModified before re-arming.

2. Orphaned DxccAutoReloadAdif setting: The toggle's AppSettings key (DxccAutoReloadAdif) is no longer read or written, but existing users will have it sitting in their settings file. Not a bug — just a minor cleanup opportunity if you want to add a one-liner to remove it on startup or in a future migration pass.

3. Flicker on locked-file retry: When onParseFailed fires, it emits importFinished (clearing "Updating..."), then re-arms the debounce timer. Two seconds later importAdifFile emits importStarted ("Updating..." again). On a file that stays locked for multiple retry cycles the stats label will toggle between "Updating..." and the old counts every ~3.5s. This is a cosmetic edge case — one option would be to not emit importFinished from onParseFailed when the debounce timer is being re-armed (i.e. keep the "Updating..." state until we actually succeed or give up).

4. parseFile() static method now diverges from parseFileAsync(): The async path gained retry logic and calls parse(f.readAll()) directly, while the static parseFile() still does a single open-or-fail. That's fine for the current usage (only parseFileAsync is called from the watcher path), but worth keeping in mind if parseFile() is used elsewhere in the future.

All changes are within the stated scope (ADIF auto-reload plumbing), no files outside that boundary. Uses AppSettings correctly where applicable. No obvious null-pointer or resource-leak risks — the QFileSystemWatcher and QTimer are member-owned with proper cleanup in setAutoReload.

Thanks for the contribution!

Comprehensive edge-case handling: atomic rename (re-arm after debounce), write-lock (3× retry), delete-recreate (directory watcher), parse failure (preserves worked status). Worker-thread msleep is correct. Settings migration is silent/non-destructive. Author's call to remove the toggle makes sense given the broken-either-way state it was in. LGTM.