chore: add a simple verify skill

Author: wu-hui

.agents/skills/verify-local-changes/SKILL.md

@@ -0,0 +1,95 @@
+---
+name: Verify Local Changes
+description: Verifies local Java SDK changes.
+---
+
+# Verify Local Changes
+
+This skill documents how to verify local code changes for the Java Firestore SDK. This should be run **every time** you complete a fix or feature and are prepared to push a pull request.
+
+## Prerequisites
+
+Ensure you have Maven installed and are in the `java-firestore` directory before running commands.
+
+---
+
+## Step 0: Format the Code
+
+Run the formatter to ensure formatting checks pass:
+
+```bash
+mvn com.spotify.fmt:fmt-maven-plugin:format
+```
+
+---
+
+## Step 1: Unit Testing (Isolated then Suite)
+
+1.  **Identify modified unit tests** in your changes.
+2.  **Run specific units only** to test isolated logic regressions:
+    ```bash
+    mvn test -Dtest=MyUnitTest#testMethod
+    ```
+3.  **Run the entire unit test suite** that contains those modified tests if the isolated unit tests pass:
+    ```bash
+    mvn test -Dtest=MyUnitTest
+    ```
+
+---
+
+## Step 2: Integration Testing (Isolated then Suite)
+
+### 💡 Integration Test Nuances (from `ITBaseTest.java`)
+
+When running integration tests, configure your execution using properties or environment variables:
+
+-   **`FIRESTORE_EDITION`**: 
+    -   `standard` (Default)
+    -   `enterprise`
+    -   *Note*: **Pipelines can only be run against `enterprise` editions**, while standard Queries run on both.
+-   **`FIRESTORE_NAMED_DATABASE`**: 
+    -   Enterprise editions usually require a named database (often `enterprise`). Adjust this flag if pointing to specific instances.
+-   **`FIRESTORE_TARGET_BACKEND`**:
+    -   `PROD` (Default)
+    -   `QA` (points to standard sandboxes)
+    -   `NIGHTLY` (points to `test-firestore.sandbox.googleapis.com:443`)
+    -   `EMULATOR` (points to `localhost:8080`)
+
+1.  **Identify modified integration tests** (usually Starting in `IT`).
+2.  **Run specific integration tests only** (isolated checks run quicker):
+    ```bash
+    mvn verify -Penable-integration-tests -DFIRESTORE_EDITION=enterprise -DFIRESTORE_NAMED_DATABASE=enterprise -Dtest=ITTest#testMethod -Dclirr.skip=true -Denforcer.skip=true -fae
+    ```
+3.  **Run the entire integration test suite** for the modified class if isolation tests pass:
+    ```bash
+    mvn verify -Penable-integration-tests -DFIRESTORE_EDITION=enterprise -DFIRESTORE_NAMED_DATABASE=enterprise -Dtest=ITTest -Dclirr.skip=true -Denforcer.skip=true -fae
+    ```
+
+
+
+---
+
+## Step 3: Full Suite Regressions
+
+Run the full integration regression suite once you are confident subsets pass:
+
+```bash
+mvn verify -Penable-integration-tests -DFIRESTORE_EDITION=enterprise -DFIRESTORE_NAMED_DATABASE=enterprise -Dclirr.skip=true -Denforcer.skip=true -fae
+```
+
+---
+
+> [!TIP]
+> Use `-Dclirr.skip=true -Denforcer.skip=true` to speed up iterations where appropriate without leaking compliance checks.
+
+---
+
+## 🛠️ Troubleshooting & Source of Truth
+
+If you run into issues executing tests with the commands above, **consult the Kokoro configuration files** as the ultimate source of truth:
+
+-   **Presubmit configurations**: See `.kokoro/presubmit/integration.cfg` (or `integration-named-db.cfg`)
+-   **Nightly configurations**: See `.kokoro/nightly/integration.cfg` 
+-   **Build shell scripts**: See `.kokoro/build.sh`
+
+These files define the exact environment variables (e.g., specific endpoints or endpoints overrides) the CI server uses!