Add schedule_timer_until absolute-deadline timer

CHANGELOG.md

@@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- **`ctx.schedule_timer_until(deadline)`** — A new absolute-deadline timer
+  variant that fires at a wall-clock `SystemTime` instead of a relative
+  `Duration`. A deadline already in the past fires immediately. It is a thin
+  constructor over the existing timer machinery (the durable record is already
+  an absolute `fire_at_ms`), so there are no changes to the action/event schema
+  or replay semantics. `schedule_timer` now shares the same internal code path.
+
 ### Changed
 
 - **`ctx.new_guid()` now returns a standard UUID v4.** The previous

src/lib.rs

@@ -3535,10 +3535,44 @@ impl OrchestrationContext {
     pub fn schedule_timer(&self, delay: std::time::Duration) -> DurableFuture<()> {
         let delay_ms = delay.as_millis() as u64;
 
+        let now = {
+            let inner = self.inner.lock().expect("Mutex should not be poisoned");
+            inner.now_ms()
+        };
+        let fire_at_ms = now.saturating_add(delay_ms);
+        self.schedule_timer_at_ms(fire_at_ms)
+    }
+
+    /// Schedule a timer that fires at an absolute wall-clock deadline.
+    ///
+    /// Equivalent to [`schedule_timer`](Self::schedule_timer) but anchored to an
+    /// absolute point in time rather than a delay from "now". A deadline already in
+    /// the past fires immediately (next turn). The deadline is recorded durably and
+    /// replayed verbatim, exactly like the existing relative timer.
+    ///
+    /// This is useful when the caller already has an absolute target time (a cron
+    /// tick, an SLA, a scheduled-at timestamp) and wants to avoid the manual
+    /// `deadline - now` clamp and the extra recorded `utc_now` reading that the
+    /// relative form would require.
+    ///
+    /// # Example
+    /// ```ignore
+    /// use std::time::{Duration, SystemTime};
+    /// let deadline = SystemTime::now() + Duration::from_secs(30);
+    /// ctx.schedule_timer_until(deadline).await;
+    /// ```
+    pub fn schedule_timer_until(&self, deadline: std::time::SystemTime) -> DurableFuture<()> {
+        let fire_at_ms = deadline
+            .duration_since(std::time::UNIX_EPOCH)
+            .map(|d| d.as_millis() as u64)
+            .unwrap_or(0);
+        self.schedule_timer_at_ms(fire_at_ms)
+    }
+
+    /// Shared timer constructor over an absolute ms-since-epoch fire time.
+    fn schedule_timer_at_ms(&self, fire_at_ms: u64) -> DurableFuture<()> {
         let mut inner = self.inner.lock().expect("Mutex should not be poisoned");
 
-        let now = inner.now_ms();
-        let fire_at_ms = now.saturating_add(delay_ms);
         let token = inner.emit_action(Action::CreateTimer {
             scheduling_event_id: 0,
             fire_at_ms,

tests/timer_tests.rs

@@ -603,3 +603,90 @@ async fn timer_fires_at_correct_time_after_previous_timer() {
         _ => panic!("Unexpected status: {status:?}"),
     }
 }
+
+// ============================================================================
+// ABSOLUTE-DEADLINE TIMER TESTS (schedule_timer_until)
+// ============================================================================
+
+#[tokio::test]
+async fn schedule_timer_until_fires_at_deadline() {
+    let (store, _td) = create_sqlite_store().await;
+
+    const DELAY_MS: u64 = 50;
+    let orch = |ctx: OrchestrationContext, _input: String| async move {
+        let deadline = std::time::SystemTime::now() + Duration::from_millis(DELAY_MS);
+        ctx.schedule_timer_until(deadline).await;
+        Ok("done".to_string())
+    };
+
+    let reg = OrchestrationRegistry::builder()
+        .register("TimerUntil", orch)
+        .build();
+    let acts = ActivityRegistry::builder().build();
+    let rt = runtime::Runtime::start_with_store(store.clone(), acts, reg).await;
+    let client = duroxide::Client::new(store.clone());
+
+    let start = std::time::Instant::now();
+    client
+        .start_orchestration("inst-until", "TimerUntil", "")
+        .await
+        .unwrap();
+
+    let status = client
+        .wait_for_orchestration("inst-until", Duration::from_secs(5))
+        .await
+        .unwrap();
+    let elapsed = start.elapsed().as_millis() as u64;
+
+    assert!(
+        elapsed >= DELAY_MS,
+        "Timer fired too early: expected >={DELAY_MS}ms, got {elapsed}ms"
+    );
+
+    match status {
+        duroxide::runtime::OrchestrationStatus::Completed { output, .. } => {
+            assert_eq!(output, "done");
+        }
+        other => panic!("Unexpected status: {other:?}"),
+    }
+
+    drop(rt);
+}
+
+#[tokio::test]
+async fn schedule_timer_until_past_deadline_fires_immediately() {
+    let (store, _td) = create_sqlite_store().await;
+
+    // A deadline well in the past should fire immediately (next turn).
+    let orch = |ctx: OrchestrationContext, _input: String| async move {
+        let deadline = std::time::UNIX_EPOCH; // far in the past
+        ctx.schedule_timer_until(deadline).await;
+        Ok("done".to_string())
+    };
+
+    let reg = OrchestrationRegistry::builder()
+        .register("TimerUntilPast", orch)
+        .build();
+    let acts = ActivityRegistry::builder().build();
+    let rt = runtime::Runtime::start_with_store(store.clone(), acts, reg).await;
+    let client = duroxide::Client::new(store.clone());
+
+    client
+        .start_orchestration("inst-until-past", "TimerUntilPast", "")
+        .await
+        .unwrap();
+
+    let status = client
+        .wait_for_orchestration("inst-until-past", Duration::from_secs(5))
+        .await
+        .unwrap();
+
+    match status {
+        duroxide::runtime::OrchestrationStatus::Completed { output, .. } => {
+            assert_eq!(output, "done");
+        }
+        other => panic!("Unexpected status: {other:?}"),
+    }
+
+    drop(rt);
+}