Two issues prevented tasks created in Thunderbird (or other CalDAV
clients) from appearing in the task view:
1. percentComplete was not in CALENDAR_TASK_PROPERTIES, so it was
never requested from the server and the heuristic check for it
was always false (dead code).
2. The hasTaskFields heuristic used strict value checks:
- 'progress' in obj && typeof obj.progress === 'string'
→ fails when Stalwart returns progress: null instead of the
RFC 8984 default "needs-action"
- 'due' in obj && obj.due != null
→ fails when Stalwart includes due: null for tasks without a
DUE date (key present, value null)
RFC 8984 §5.2 defines due, progress and percentComplete as Task-only
properties — a VEVENT will never include them in a JMAP response.
Checking for key presence alone (even when null) is therefore a
reliable discriminator, regardless of the actual value.
