diff --git a/src/ingest/merge.ts b/src/ingest/merge.ts
new file mode 100644
index 0000000..69a29a6
--- /dev/null
+++ b/src/ingest/merge.ts
@@ -0,0 +1,174 @@
+import type { GachaEvent } from "../shared/schema.ts";
+
+/**
+ * Combine events for one game from several sources.
+ *
+ * Two sources covering the same game will disagree: different titles for the
+ * same event, dates that differ by a day, one listing something the other
+ * misses. This decides what the feed shows.
+ *
+ * The rules, in order:
+ *   1. Same event ID  → same event. Keep the higher-confidence copy.
+ *   2. Near match     → same event under different titles. Keep the
+ *                       higher-confidence copy and record corroboration.
+ *   3. Otherwise      → distinct events; keep both.
+ *
+ * Corroboration is the point of running multiple sources: two independent
+ * sources agreeing on a date is much stronger evidence than one asserting it,
+ * and that shows up as a confidence bump. Two sources *disagreeing* on an end
+ * date is flagged rather than silently resolved — see `conflicts`.
+ */
+
+export interface MergeResult {
+  events: GachaEvent[];
+  /**
+   * Pairs that look like the same event but disagree on an end date by more
+   * than the tolerance. These are the cases a human should look at; the
+   * pipeline routes them to quarantine.
+   */
+  conflicts: Array<{
+    kept: GachaEvent;
+    rejected: GachaEvent;
+    field: "endsAt" | "startsAt";
+    deltaHours: number;
+  }>;
+}
+
+export interface MergeOptions {
+  /** How far two boundaries may differ and still count as agreement. */
+  toleranceHours?: number;
+  /** Title similarity above which two events are considered the same. */
+  titleThreshold?: number;
+  /** Confidence added when an independent source agrees. */
+  corroborationBonus?: number;
+}
+
+const DEFAULTS = {
+  toleranceHours: 24,
+  /**
+   * 0.8, not higher: a two-word title with one extra decorative token
+   * ("Stygian Onslaught" vs "Stygian Onslaught Event") scores exactly 0.8, and
+   * failing to merge those puts duplicate rows in front of the user. The real
+   * guard against false positives is start-date proximity, not this number — a
+   * rerun reuses the name but starts months later.
+   */
+  titleThreshold: 0.8,
+  corroborationBonus: 0.1,
+} as const;
+
+export function mergeEvents(
+  groups: GachaEvent[][],
+  options: MergeOptions = {},
+): MergeResult {
+  const toleranceHours = options.toleranceHours ?? DEFAULTS.toleranceHours;
+  const titleThreshold = options.titleThreshold ?? DEFAULTS.titleThreshold;
+  const bonus = options.corroborationBonus ?? DEFAULTS.corroborationBonus;
+
+  const kept: GachaEvent[] = [];
+  const conflicts: MergeResult["conflicts"] = [];
+
+  for (const incoming of groups.flat()) {
+    const matchIndex = kept.findIndex(
+      (existing) =>
+        existing.game === incoming.game &&
+        isSameEvent(existing, incoming, titleThreshold, toleranceHours),
+    );
+
+    if (matchIndex === -1) {
+      kept.push(incoming);
+      continue;
+    }
+
+    const existing = kept[matchIndex];
+    if (existing === undefined) continue;
+
+    const conflict = findConflict(existing, incoming, toleranceHours);
+    const [winner, loser] =
+      incoming.confidence > existing.confidence
+        ? ([incoming, existing] as const)
+        : ([existing, incoming] as const);
+
+    if (conflict !== null) {
+      // Independent sources disagree on when this ends. Do not average, do not
+      // silently prefer one — surface it. A wrong end date is the failure this
+      // product exists to prevent.
+      conflicts.push({ kept: winner, rejected: loser, ...conflict });
+      kept[matchIndex] = winner;
+      continue;
+    }
+
+    // Agreement from a different source is real evidence; from the same source
+    // it is just the same row seen twice.
+    const corroborated =
+      winner.sourceId !== loser.sourceId
+        ? { ...winner, confidence: Math.min(1, winner.confidence + bonus) }
+        : winner;
+
+    kept[matchIndex] = corroborated;
+  }
+
+  kept.sort((a, b) =>
+    a.startsAt === b.startsAt
+      ? a.id.localeCompare(b.id)
+      : a.startsAt.localeCompare(b.startsAt),
+  );
+
+  return { events: kept, conflicts };
+}
+
+function isSameEvent(
+  a: GachaEvent,
+  b: GachaEvent,
+  titleThreshold: number,
+  toleranceHours: number,
+): boolean {
+  if (a.id === b.id) return true;
+  if (titleSimilarity(a.title, b.title) < titleThreshold) return false;
+  // Similar titles are not enough — reruns reuse names. Require the start dates
+  // to be close before treating two entries as one event.
+  return hoursBetween(a.startsAt, b.startsAt) <= toleranceHours;
+}
+
+function findConflict(
+  a: GachaEvent,
+  b: GachaEvent,
+  toleranceHours: number,
+): { field: "endsAt" | "startsAt"; deltaHours: number } | null {
+  if (a.endsAt !== null && b.endsAt !== null) {
+    const delta = hoursBetween(a.endsAt, b.endsAt);
+    if (delta > toleranceHours) return { field: "endsAt", deltaHours: delta };
+  }
+  const startDelta = hoursBetween(a.startsAt, b.startsAt);
+  if (startDelta > toleranceHours) {
+    return { field: "startsAt", deltaHours: startDelta };
+  }
+  return null;
+}
+
+function hoursBetween(a: string, b: string): number {
+  return Math.abs(Date.parse(a) - Date.parse(b)) / 3_600_000;
+}
+
+/**
+ * Token-overlap (Dice) similarity on normalised titles. Deliberately simple:
+ * it only needs to catch "Stygian Onslaught" vs "Stygian Onslaught (Event)",
+ * not to do fuzzy natural-language matching.
+ */
+export function titleSimilarity(a: string, b: string): number {
+  const ta = tokens(a);
+  const tb = tokens(b);
+  if (ta.size === 0 || tb.size === 0) return 0;
+  let shared = 0;
+  for (const t of ta) if (tb.has(t)) shared += 1;
+  return (2 * shared) / (ta.size + tb.size);
+}
+
+function tokens(title: string): Set<string> {
+  return new Set(
+    title
+      .toLowerCase()
+      .replace(/[^a-z0-9\s]/g, " ")
+      .split(/\s+/)
+      .filter((w) => w.length > 0),
+  );
+}
diff --git a/test/merge.test.ts b/test/merge.test.ts
new file mode 100644
index 0000000..0fd3c0a
--- /dev/null
+++ b/test/merge.test.ts
@@ -0,0 +1,136 @@
+import { describe, expect, test } from "bun:test";
+import { mergeEvents, titleSimilarity } from "../src/ingest/merge.ts";
+import type { GachaEvent } from "../src/shared/schema.ts";
+
+const NOW = "2026-08-14T00:00:00.000Z";
+
+function event(overrides: Partial<GachaEvent> = {}): GachaEvent {
+  return {
+    id: "genshin:test-event:2026-08-12",
+    game: "genshin",
+    title: "Test Event",
+    type: "other",
+    summary: null,
+    startsAt: "2026-08-12T00:00:00.000Z",
+    startPrecision: "day",
+    endsAt: "2026-08-24T00:00:00.000Z",
+    endPrecision: "day",
+    regionScoped: false,
+    regionEnds: null,
+    sourceUrl: "https://example.test/a",
+    sourceId: "source-a",
+    status: "published",
+    confidence: 0.9,
+    extractionMethod: "parser",
+    version: 1,
+    firstSeenAt: NOW,
+    updatedAt: NOW,
+    ...overrides,
+  };
+}
+
+describe("mergeEvents", () => {
+  test("keeps distinct events from different sources", () => {
+    const a = event({ id: "genshin:a:2026-08-12", title: "Alpha" });
+    const b = event({
+      id: "genshin:b:2026-09-01",
+      title: "Beta",
+      startsAt: "2026-09-01T00:00:00.000Z",
+      endsAt: "2026-09-10T00:00:00.000Z",
+      sourceId: "source-b",
+    });
+    const { events, conflicts } = mergeEvents([[a], [b]]);
+    expect(events).toHaveLength(2);
+    expect(conflicts).toHaveLength(0);
+  });
+
+  test("collapses the same event seen by two sources", () => {
+    const a = event({ sourceId: "source-a", confidence: 0.85 });
+    const b = event({ sourceId: "source-b", confidence: 0.9 });
+    const { events } = mergeEvents([[a], [b]]);
+    expect(events).toHaveLength(1);
+  });
+
+  test("raises confidence when an independent source corroborates", () => {
+    const a = event({ sourceId: "source-a", confidence: 0.85 });
+    const b = event({ sourceId: "source-b", confidence: 0.85 });
+    const { events } = mergeEvents([[a], [b]]);
+    // Two sources independently agreeing is stronger evidence than one.
+    expect(events[0]?.confidence).toBeCloseTo(0.95, 5);
+  });
+
+  test("does not corroborate a duplicate from the same source", () => {
+    const a = event({ sourceId: "source-a", confidence: 0.85 });
+    const { events } = mergeEvents([[a, { ...a }]]);
+    expect(events).toHaveLength(1);
+    expect(events[0]?.confidence).toBeCloseTo(0.85, 5);
+  });
+
+  test("matches the same event under slightly different titles", () => {
+    const a = event({ title: "Stygian Onslaught", sourceId: "source-a" });
+    const b = event({
+      id: "genshin:stygian-onslaught-event:2026-08-12",
+      title: "Stygian Onslaught Event",
+      sourceId: "source-b",
+    });
+    const { events } = mergeEvents([[a], [b]]);
+    expect(events).toHaveLength(1);
+  });
+
+  test("flags an end-date disagreement instead of picking silently", () => {
+    const a = event({ sourceId: "source-a", confidence: 0.9 });
+    const b = event({
+      sourceId: "source-b",
+      confidence: 0.8,
+      endsAt: "2026-08-28T00:00:00.000Z", // 4 days later
+    });
+    const { events, conflicts } = mergeEvents([[a], [b]]);
+    expect(events).toHaveLength(1);
+    expect(conflicts).toHaveLength(1);
+    expect(conflicts[0]?.field).toBe("endsAt");
+    expect(conflicts[0]?.deltaHours).toBe(96);
+    // The conflict is surfaced, not averaged away, and confidence is NOT
+    // bumped — disagreement is the opposite of corroboration.
+    expect(events[0]?.confidence).toBeCloseTo(0.9, 5);
+  });
+
+  test("treats a same-name rerun months later as a separate event", () => {
+    const a = event({ title: "Windblume Festival" });
+    const b = event({
+      id: "genshin:windblume-festival:2027-03-01",
+      title: "Windblume Festival",
+      startsAt: "2027-03-01T00:00:00.000Z",
+      endsAt: "2027-03-20T00:00:00.000Z",
+      sourceId: "source-b",
+    });
+    const { events } = mergeEvents([[a], [b]]);
+    expect(events).toHaveLength(2);
+  });
+
+  test("returns events sorted by start date", () => {
+    const late = event({
+      id: "genshin:late:2026-09-01",
+      title: "Late",
+      startsAt: "2026-09-01T00:00:00.000Z",
+      endsAt: "2026-09-05T00:00:00.000Z",
+    });
+    const early = event({ id: "genshin:early:2026-08-01", title: "Early",
+      startsAt: "2026-08-01T00:00:00.000Z" });
+    const { events } = mergeEvents([[late], [early]]);
+    expect(events.map((e) => e.title)).toEqual(["Early", "Late"]);
+  });
+});
+
+describe("titleSimilarity", () => {
+  test("identical titles score 1", () => {
+    expect(titleSimilarity("Stygian Onslaught", "Stygian Onslaught")).toBe(1);
+  });
+
+  test("ignores case and punctuation", () => {
+    expect(titleSimilarity("Gold Clash!", "gold clash")).toBe(1);
+  });
+
+  test("unrelated titles score low", () => {
+    expect(titleSimilarity("Gold Clash", "Fishing Frenzy")).toBeLessThan(0.3);
+  });
+});