diff --git a/src/tests/atomic_mutation_operations.test.ts b/src/tests/atomic_mutation_operations.test.ts
new file mode 100644
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--- /dev/null
+++ b/src/tests/atomic_mutation_operations.test.ts
@@ -0,0 +1,344 @@
+import { expect } from "chai";
+import { randomUUID } from "node:crypto";
+import {
+  Schema,
+  type AtomicDelete,
+  type AtomicMutation,
+  type AtomicUpdate,
+  type AtomicEqualityValue,
+} from "@antelopejs/interface-database";
+
+interface NestedData {
+  removed?: boolean;
+  retained?: string;
+  stage?: string;
+  args?: string[];
+  left?: boolean;
+  right?: boolean;
+}
+
+interface AtomicRecord {
+  _id: string;
+  revision?: string | null;
+  value: string;
+  nested?: NestedData;
+  equal?: AtomicEqualityValue | null;
+  expires?: Date;
+}
+
+interface AtomicTables {
+  records: AtomicRecord;
+}
+
+const schema = new Schema<AtomicTables>("atomic-provider-contract", {
+  records: { fields: { value: "string", expires: "date" }, indexes: {} },
+});
+const owner = schema.instance("owner").table("records");
+const other = schema.instance("other").table("records");
+const defaults = schema.instance().table("records");
+const initialRevision = "initial";
+const raceRounds = 8;
+const expiry = new Date("2026-01-05T10:00:00+02:00");
+const sameExpiry = new Date("2026-01-05T08:00:00Z");
+const differentExpiry = new Date("2026-01-05T08:00:01Z");
+
+function Update(value: string): AtomicUpdate<AtomicRecord> {
+  return {
+    type: "update",
+    revisionField: "revision",
+    expectedRevision: initialRevision,
+    nextRevision: `revision-${value}`,
+    patch: { value },
+  };
+}
+
+const deletion: AtomicDelete<AtomicRecord> = {
+  type: "delete",
+  revisionField: "revision",
+  expectedRevision: initialRevision,
+};
+const equalityDeletion: AtomicMutation<AtomicRecord> = {
+  type: "deleteIfEqual",
+  field: "value",
+  expectedValue: "original",
+};
+
+async function Insert(data: Partial<AtomicRecord> = {}) {
+  const key = randomUUID();
+  await owner.insert({
+    _id: key,
+    revision: initialRevision,
+    value: "original",
+    ...data,
+  });
+  return key;
+}
+
+describe("Atomic mutation provider conformance", () => {
+  before(async () => {
+    await schema.createInstance("owner");
+    await schema.createInstance("other");
+    await schema.createInstance();
+  });
+  after(async () => {
+    await schema.destroyInstance("owner");
+    await schema.destroyInstance("other");
+    await schema.destroyInstance();
+  });
+  it("persists revisions and replaces fields literally", ReplaceFields);
+  it("advances revision when the payload is unchanged", UnchangedPatch);
+  it("leaves stale updates and deletes unchanged", StaleRevision);
+  it("never upserts missing identities for any mutation", MissingIdentity);
+  it("isolates named and default instances", IsolateInstances);
+  it("updates and deletes records in the default instance", DefaultInstance);
+  it("bootstraps absence, never null or missing rows", MissingRevision);
+  it("deletes only absent revisions", DeleteMissingRevision);
+  it("preserves scalar types and checks equality at deletion", ScalarEquality);
+  it("compares declared dates by instant", DateEquality);
+  it("applies one competing update with its full patch", CompetingUpdates);
+  it("serializes revision deletion against update", CompetingRevisionDelete);
+  it("protects refreshes from scalar cleanup", CompetingEqualityDelete);
+});
+
+async function ReplaceFields() {
+  const key = await Insert({ nested: { removed: true, retained: "old" } });
+  expect((await owner.get(key)).revision).to.equal(initialRevision);
+  const nested = { retained: "$literal", stage: "delete", args: ["data"] };
+  const request = { ...Update("unused"), patch: { nested } };
+  expect(await owner.atomicMutation(key, request)).to.equal("applied");
+  const stored = await owner.get(key);
+  expect(stored.nested).to.deep.equal(nested);
+  expect(stored.value).to.equal("original");
+  expect(stored.revision).to.equal(request.nextRevision);
+}
+
+async function UnchangedPatch() {
+  const key = await Insert();
+  expect(await owner.atomicMutation(key, Update("original"))).to.equal(
+    "applied",
+  );
+  expect(await owner.get(key)).to.include({
+    value: "original",
+    revision: "revision-original",
+  });
+}
+
+async function StaleRevision() {
+  const key = await Insert();
+  const count = await owner.count();
+  expect(await owner.atomicMutation(key, Update("fresh"))).to.equal("applied");
+  expect(await owner.atomicMutation(key, Update("stale"))).to.equal(
+    "not-applied",
+  );
+  expect(await owner.atomicMutation(key, deletion)).to.equal("not-applied");
+  expect(await owner.count()).to.equal(count);
+  expect(await owner.get(key)).to.include({
+    value: "fresh",
+    revision: "revision-fresh",
+  });
+  expect(
+    await owner.atomicMutation(key, {
+      ...deletion,
+      expectedRevision: "revision-fresh",
+    }),
+  ).to.equal("applied");
+  expect(await owner.get(key)).to.equal(undefined);
+  expect(await owner.count()).to.equal(count - 1);
+  expect(await owner.atomicMutation(key, deletion)).to.equal("not-applied");
+}
+
+async function MissingIdentity() {
+  const key = randomUUID();
+  const count = await owner.count();
+  for (const request of [Update("absent"), deletion, equalityDeletion]) {
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+    expect(await owner.get(key)).to.equal(undefined);
+    expect(await owner.count()).to.equal(count);
+  }
+}
+
+async function IsolateInstances() {
+  const key = await Insert();
+  const ownerCount = await owner.count();
+  for (const table of [other, defaults]) {
+    const count = await table.count();
+    for (const request of [Update("intruder"), deletion, equalityDeletion]) {
+      expect(await table.atomicMutation(key, request)).to.equal("not-applied");
+      expect(await table.get(key)).to.equal(undefined);
+      expect(await table.count()).to.equal(count);
+      expect(await owner.count()).to.equal(ownerCount);
+      expect(await owner.get(key)).to.include({
+        value: "original",
+        revision: initialRevision,
+      });
+    }
+  }
+}
+
+async function DefaultInstance() {
+  const key = randomUUID();
+  expect(await defaults.atomicMutation(key, Update("default"))).to.equal(
+    "not-applied",
+  );
+  await defaults.insert({
+    _id: key,
+    revision: initialRevision,
+    value: "original",
+  });
+  expect(await defaults.atomicMutation(key, Update("default"))).to.equal(
+    "applied",
+  );
+  expect(await defaults.get(key)).to.include({
+    value: "default",
+    revision: "revision-default",
+  });
+  expect(
+    await defaults.atomicMutation(key, {
+      ...deletion,
+      expectedRevision: "revision-default",
+    }),
+  ).to.equal("applied");
+  expect(await defaults.get(key)).to.equal(undefined);
+}
+
+async function MissingRevision() {
+  const absent = randomUUID();
+  const storedNull = await Insert({ revision: null });
+  const missingRow = randomUUID();
+  await owner.insert({ _id: absent, value: "legacy" });
+  const request: AtomicUpdate<AtomicRecord> = {
+    ...Update("adopted"),
+    expectedRevision: { kind: "missing" },
+  };
+  for (const key of [storedNull, missingRow]) {
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+  }
+  expect(await owner.atomicMutation(absent, request)).to.equal("applied");
+  expect(await owner.atomicMutation(absent, request)).to.equal("not-applied");
+  expect(await owner.get(absent)).to.include({
+    value: "adopted",
+    revision: "revision-adopted",
+  });
+  expect((await owner.get(storedNull)).revision).to.equal(null);
+  expect(await owner.get(missingRow)).to.equal(undefined);
+}
+
+async function DeleteMissingRevision() {
+  const absent = randomUUID();
+  const storedNull = await Insert({ revision: null });
+  const present = await Insert();
+  const missingRow = randomUUID();
+  await owner.insert({ _id: absent, value: "legacy" });
+  const request: AtomicMutation<AtomicRecord> = {
+    ...deletion,
+    expectedRevision: { kind: "missing" },
+  };
+  for (const key of [storedNull, present, missingRow]) {
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+  }
+  expect(await owner.atomicMutation(absent, request)).to.equal("applied");
+  expect(await owner.get(absent)).to.equal(undefined);
+  expect((await owner.get(storedNull)).revision).to.equal(null);
+  expect((await owner.get(present)).revision).to.equal(initialRevision);
+  expect(await owner.get(missingRow)).to.equal(undefined);
+}
+
+async function ScalarEquality() {
+  for (const expectedValue of ["saved", 0, false]) {
+    const key = await Insert();
+    const request: AtomicMutation<AtomicRecord> = {
+      type: "deleteIfEqual",
+      field: "equal",
+      expectedValue,
+    };
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+    await owner.get(key).update({ equal: null });
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+    await owner.get(key).update({ equal: expectedValue });
+    expect(await other.atomicMutation(key, request)).to.equal("not-applied");
+    expect(
+      await owner.atomicMutation(key, {
+        ...request,
+        expectedValue: `${expectedValue}-different`,
+      }),
+    ).to.equal("not-applied");
+    expect(
+      await owner.atomicMutation(key, {
+        ...request,
+        expectedValue: expectedValue === 0 ? "0" : 0,
+      }),
+    ).to.equal("not-applied");
+    expect((await owner.get(key)).equal).to.equal(expectedValue);
+    expect(await owner.atomicMutation(key, request)).to.equal("applied");
+    expect(await owner.get(key)).to.equal(undefined);
+    expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+  }
+}
+
+async function DateEquality() {
+  const key = await Insert();
+  const request: AtomicMutation<AtomicRecord> = {
+    type: "deleteIfEqual",
+    field: "expires",
+    expectedValue: sameExpiry,
+  };
+  expect(await owner.atomicMutation(key, request)).to.equal("not-applied");
+  await owner.get(key).update({ expires: expiry });
+  expect(
+    await owner.atomicMutation(key, {
+      ...request,
+      expectedValue: differentExpiry,
+    }),
+  ).to.equal("not-applied");
+  expect((await owner.get(key)).expires).to.deep.equal(expiry);
+  expect(await owner.atomicMutation(key, request)).to.equal("applied");
+  expect(await owner.get(key)).to.equal(undefined);
+}
+
+async function CompetingUpdates() {
+  for (let round = 0; round < raceRounds; round++) {
+    const key = await Insert();
+    const requests = [Update("left"), Update("right")];
+    requests[0].patch.nested = { left: true };
+    requests[1].patch.nested = { right: true };
+    const outcomes = await Promise.all(
+      requests.map((request) => owner.atomicMutation(key, request).run()),
+    );
+    expect([...outcomes].sort()).to.deep.equal(["applied", "not-applied"]);
+    const winner = requests[outcomes.indexOf("applied")];
+    expect(await owner.get(key)).to.include({
+      revision: winner.nextRevision,
+      value: winner.patch.value,
+    });
+    expect((await owner.get(key)).nested).to.deep.equal(winner.patch.nested);
+  }
+}
+
+async function CompeteDeletion(request: AtomicMutation<AtomicRecord>) {
+  const requests = [request, Update("refreshed")];
+  for (let round = 0; round < raceRounds; round++) {
+    const key = await Insert();
+    requests.reverse();
+    const outcomes = await Promise.all(
+      requests.map((mutation) => owner.atomicMutation(key, mutation).run()),
+    );
+    expect([...outcomes].sort()).to.deep.equal(["applied", "not-applied"]);
+    const stored = await owner.get(key);
+    if (requests[outcomes.indexOf("applied")].type !== "update") {
+      expect(stored).to.equal(undefined);
+      continue;
+    }
+    expect(stored).to.include({
+      value: "refreshed",
+      revision: "revision-refreshed",
+    });
+  }
+}
+
+async function CompetingRevisionDelete() {
+  await CompeteDeletion(deletion);
+}
+
+async function CompetingEqualityDelete() {
+  await CompeteDeletion(equalityDeletion);
+}