I guess I'm asking how fragile this is in practice.
- Deleting a Reminder that has been synced to Obisidian deletes the Task from Obsidian (if enabled in the settings menu)
- Completing a synced task in Obsidian will complete the Reminder (on the next sync)
- Completing a synced Reminder will complete the Task in Obsidian (immediately if the app is running)
- Creating a Reminder in the synced list creates a task in a note called "Reminder Sync Inbox.md"
- Editing a Task in Obsidian and syncing deletes the previously associated Reminder and creates a new one (effectively updating the text in Reminders.app)
The only known limitation (so far) is:
- Editing a synced Reminder description in Reminders.app does not update the text of the Task in Obsidian: This is hard to solve as the original Task may contain embedded links (which are stripped to just the link text for the Reminder description). Syncing those edits back to Markdown is a difficult problem that I haven't bothered focused on yet as I feel it may not be solvable.
In case of a conflict, the state in Obsidian always wins :)