diff --git a/AGENTS.md b/AGENTS.md
index 10d1ec63a..379b3c47e 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -27,6 +27,9 @@ It captures practical rules that prevent avoidable CI and PR churn.
 - If new learnings or misunderstandings are discovered, propose an `AGENTS.md` update in the same PR.
 - In docs Markdown, keep `<!--codeinclude-->` blocks tight with no blank lines between the markers and the include line, or the rendered snippet will contain blank lines between code lines.
 - Codeinclude `inside_block:<name>` selects the block after the first line that contains `<name>` anywhere, so a marker whose name also appears earlier in the file (for example inside another marker's name) silently includes the wrong block. The `Docs` workflow runs `mkdocs build --strict`, which fails when a marker or included file is missing but cannot catch this.
+- Fix the root cause. A change that only makes a failure less likely is not a fix.
+  - Arbitrary delays (`sleep`), repeating a check, or adding retries do not remove a race; they hide it.
+  - For readiness problems, wait on a deterministic signal of the state you need. If no such signal exists, say so rather than shipping a mitigation as a fix.
 - Tests should verify observable behavior changes, not only internal/config state.
   - Example: for a security option, assert a real secure/insecure behavior difference.
 - Tests should not pull container images that the test suite does not already pull.
diff --git a/packages/modules/mongodb/src/mongodb-atlas-local-container.test.ts b/packages/modules/mongodb/src/mongodb-atlas-local-container.test.ts
index fa6dd7a3e..44d0a4960 100644
--- a/packages/modules/mongodb/src/mongodb-atlas-local-container.test.ts
+++ b/packages/modules/mongodb/src/mongodb-atlas-local-container.test.ts
@@ -61,7 +61,7 @@ describe("MongoDBAtlasLocalContainer", { timeout: 240_000 }, () => {
   it("should connect to mongodb atlas local", async () => {
     await using container = await new MongoDBAtlasLocalContainer(IMAGE).start();
 
-    const db = mongoose.createConnection(container.getConnectionString(), { directConnection: true });
+    const db = await mongoose.createConnection(container.getConnectionString(), { directConnection: true }).asPromise();
 
     const obj = { value: 1 };
     const collection = db.collection("test");
@@ -79,7 +79,9 @@ describe("MongoDBAtlasLocalContainer", { timeout: 240_000 }, () => {
       .withPassword("customPassword")
       .start();
 
-    const db = mongoose.createConnection(container.getDatabaseConnectionString(), { directConnection: true });
+    const db = await mongoose
+      .createConnection(container.getDatabaseConnectionString(), { directConnection: true })
+      .asPromise();
 
     const obj = { value: 1 };
     const collection = db.collection("test");
@@ -95,10 +97,12 @@ describe("MongoDBAtlasLocalContainer", { timeout: 240_000 }, () => {
     // createAtlasIndexAndSearchIt {
     await using atlasLocalContainer = await new MongoDBAtlasLocalContainer(IMAGE).start();
 
-    const db = mongoose.createConnection(atlasLocalContainer.getConnectionString(), {
-      dbName: "test",
-      directConnection: true,
-    });
+    const db = await mongoose
+      .createConnection(atlasLocalContainer.getConnectionString(), {
+        dbName: "test",
+        directConnection: true,
+      })
+      .asPromise();
 
     try {
       const collection = db.collection("test");
diff --git a/packages/modules/mongodb/src/mongodb-container.test.ts b/packages/modules/mongodb/src/mongodb-container.test.ts
index e6c014f40..d44864e9e 100644
--- a/packages/modules/mongodb/src/mongodb-container.test.ts
+++ b/packages/modules/mongodb/src/mongodb-container.test.ts
@@ -9,7 +9,7 @@ describe("MongoDBContainer", { timeout: 240_000 }, () => {
     // connectMongo {
     await using container = await new MongoDBContainer(image).start();
 
-    const db = mongoose.createConnection(container.getConnectionString(), { directConnection: true });
+    const db = await mongoose.createConnection(container.getConnectionString(), { directConnection: true }).asPromise();
 
     const obj = { value: 1 };
     const collection = db.collection("test");
@@ -30,7 +30,7 @@ describe("MongoDBContainer", { timeout: 240_000 }, () => {
       .start();
     // }
 
-    const db = mongoose.createConnection(container.getConnectionString(), { directConnection: true });
+    const db = await mongoose.createConnection(container.getConnectionString(), { directConnection: true }).asPromise();
 
     const result = await db.collection("test").insertOne({ title: "test" });
     const resultId = result.insertedId.toString();