WP-02: contracts and failing tests for settings, mail, jobs and scheduler

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/application/src/scheduler.rs

@@ -0,0 +1,30 @@
+//! Cron scheduler: decides which scheduled job kinds are due.
+use chrono::{DateTime, Utc};
+use domain::jobs::JobKind;
+use domain::DomainError;
+
+/// Validate a 6-field cron expression (seconds first).
+pub fn validate_cron(_expr: &str) -> Result<(), DomainError> {
+    todo!()
+}
+
+/// Next fire time strictly after `after`.
+pub fn next_fire(_expr: &str, _after: DateTime<Utc>) -> Option<DateTime<Utc>> {
+    todo!()
+}
+
+/// A job is due if a fire time exists in `(last_run, now]`. With no last run, it is due
+/// if a fire time falls within the last `grace` seconds, so a fresh start does not
+/// immediately run every job.
+pub fn is_due(
+    _expr: &str,
+    _last_run: Option<DateTime<Utc>>,
+    _now: DateTime<Utc>,
+    _grace_secs: i64,
+) -> bool {
+    todo!()
+}
+
+pub struct Scheduler {
+    pub kinds: Vec<JobKind>,
+}