feat(recurring): close the two cadence vocabularies and separate them

[lessevv]

Summary

• C2-R20 closes the series cadence vocabulary to weekly, monthly, quarterly, yearly, irregular.
• C8-R22 closes the digest cadence vocabulary to daily, weekly, off.
• Both require one named type rather than free strings, and a constrained column. Both state that the two vocabularies are distinct and must not share a type.

Why

Two different closed sets are both called "cadence", both are carried as free strings, and they overlap on the value weekly. Nothing in the spec says they are different things, and nothing in the product stops a value outside either set from being written.

The series cadence is already described in C2's prose — "snaps to a named cadence — weekly, monthly, quarterly, yearly — or declares the series irregular" — but never required to be closed. The consequence is visible in the schema: in the same migration that creates recurring_series, the state column gets a CHECK constraint built from an explicit allowed list, while cadence gets a bare string(24) with a default. Two closed vocabularies on one table, governed differently, with nothing in the spec to say the second one is closed at all.

The digest cadence is referenced in C8 only as "the user's chosen cadence". What may be chosen is daily, weekly, or off, which appears nowhere except in the code that reads it.

The overlap is the part worth being explicit about. Both sets contain weekly, so a single shared type is an easy and wrong simplification: it would let a digest preference of off be assigned to a series, and a series cadence of quarterly be assigned to a digest. C8-R22 says they must not share a type for that reason.

What this enables

Implementation is a follow-up in beatrax, citing these identifiers: a backed enum per vocabulary, and a CHECK constraint on each column matching how recurring_series.state is already governed.

It also removes a cause rather than a symptom. The cadence literals appear a few hundred times across Recurring, Forecasting, Calendar, Notifications, DriftAlerts and Position, and the duplicated-literal findings that keep surfacing there are that absence of a type showing through.

Checklist

• just integrity — spec integrity clean
• typos clean on both changed files
• Requirements appended, never renumbered (GOV-R10) — C2 ends at R19, C8 at R21
• Both new rows are MUST, testable, and name the vocabulary explicitly
• The cross-reference between C2 and C8 is bidirectional
• Commit is signed off and carries a Spec: trailer

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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