Recurring tasks repeat in the document

Context

ADR-0053 put a task's due date on its checklist line so Markdown, exports and other editors keep it. A repeating chore ("water the plants every week") needs a rule as well as a date, and completing it has to leave a record that it was done while scheduling the next one.

Decision

• The rule is a recurrence attribute on check_item, stored in its canonical Obsidian Tasks spelling: every day, every weekday, or every [N] day|week|month|year[s]. Rules Skriuw cannot compute stay literal text rather than being half-understood.
• Markdown writes it as the recurrence signifier before the due date, which stays last: - [ ] Water plants <!--skriuw-task:t:b--> 🔁 every week 📅 2026-10-01. The parser reads marker, rule and date in any order and in any letter case.
• Completing a repeating item keeps it checked and inserts the next occurrence directly below it, unchecked, due on the next date counted from its own due date, or from today when it had none. Months and years keep the day of the month, clamped to the end of shorter months. Unchecking never removes or adds an occurrence.
• A linked task's next occurrence gets a fresh task and block identity, so the completed record keeps its history and the new item is a task of its own. In the editor the toggle and the insertion are one transaction, and the next save promotes the new item. In the tasks view the paired update_task writes both items and a create_task in the same batch creates the next record, after the document that proves its link.
• In the editor, typing every:<rule> and a space on a checklist line sets the rule; its chip turns back into that token on Enter or click and stops the repeat on Delete.

Consequences

• No schema or contract change: the rule is document content, and the task record does not store it.
• The mobile tasks surface ticks the checkbox through a Markdown line rewrite and does not insert the next occurrence; it keeps the rule intact, so the next occurrence appears when the task is completed on desktop or in the browser.
• Obsidian Tasks' richer rules (every week on Sunday, when done) are not computed.