diff --git a/src/core/timeline.js b/src/core/timeline.js
new file mode 100644
index 0000000..7b49d6f
--- /dev/null
+++ b/src/core/timeline.js
@@ -0,0 +1,20 @@
+export function sortedTimeline(timeline) {
+  return [...timeline].sort((a, b) => a.targetMin - b.targetMin);
+}
+
+export function nextUnreachedBeat(timeline, stamps) {
+  const t = sortedTimeline(timeline);
+  return t.find((b) => !(b.id in stamps)) || null;
+}
+
+export function analyze(timeline, elapsedMin, stamps) {
+  const t = sortedTimeline(timeline);
+  const reached = t.filter((b) => b.id in stamps);
+  const currentBeat = reached.length ? reached[reached.length - 1] : null;
+  const currentIndex = currentBeat ? t.findIndex((b) => b.id === currentBeat.id) : -1;
+  const nextBeat = t[currentIndex + 1] || null;
+  const nextHardTrigger = t.slice(currentIndex + 1).find((b) => b.hardTrigger) || null;
+  const minutesToNextHard = nextHardTrigger ? nextHardTrigger.targetMin - elapsedMin : null;
+  const driftMin = currentBeat ? stamps[currentBeat.id] - currentBeat.targetMin : null;
+  return { currentBeat, nextBeat, nextHardTrigger, minutesToNextHard, driftMin, cutHint: nextBeat?.cutHint ?? null };
+}
diff --git a/tests/core/timeline.test.js b/tests/core/timeline.test.js
new file mode 100644
index 0000000..e85fa0a
--- /dev/null
+++ b/tests/core/timeline.test.js
@@ -0,0 +1,39 @@
+import { describe, it, expect } from 'vitest';
+import { sortedTimeline, nextUnreachedBeat, analyze } from '../../src/core/timeline.js';
+
+const T = [
+  { id: 'a', act: 1, label: 'Open', targetMin: 0, hardTrigger: true },
+  { id: 'b', act: 1, label: 'Parlor', targetMin: 35, cutHint: 'skip the tea' },
+  { id: 'c', act: 2, label: 'Door-cam', targetMin: 120, hardTrigger: true },
+];
+
+describe('timeline analysis', () => {
+  it('sorts by targetMin without mutating input', () => {
+    const shuffled = [T[2], T[0], T[1]];
+    expect(sortedTimeline(shuffled).map((b) => b.id)).toEqual(['a', 'b', 'c']);
+    expect(shuffled[0].id).toBe('c');
+  });
+
+  it('finds the next unreached beat', () => {
+    expect(nextUnreachedBeat(T, {}).id).toBe('a');
+    expect(nextUnreachedBeat(T, { a: 0 }).id).toBe('b');
+  });
+
+  it('before any stamp: no current, next hard is the first hard beat', () => {
+    const m = analyze(T, 5, {});
+    expect(m.currentBeat).toBe(null);
+    expect(m.nextBeat.id).toBe('a');
+    expect(m.driftMin).toBe(null);
+    expect(m.nextHardTrigger.id).toBe('a');
+  });
+
+  it('after stamping "a" late: drift is behind, next hard is "c"', () => {
+    const m = analyze(T, 40, { a: 6 }); // reached Open at 6 min (target 0) => 6 behind
+    expect(m.currentBeat.id).toBe('a');
+    expect(m.driftMin).toBe(6);
+    expect(m.nextBeat.id).toBe('b');
+    expect(m.cutHint).toBe('skip the tea');
+    expect(m.nextHardTrigger.id).toBe('c');
+    expect(m.minutesToNextHard).toBe(80); // 120 - 40
+  });
+});