docs: improve tree shaking docs

docsite/docs/guides/bundling.mdx

@@ -277,6 +277,9 @@ Tree shaking is _off_ by default. You can control it with the
 }
 ```
 
+For setup details, options, bundle-size checks, and known limitations, see the
+[`@rnx-kit/metro-serializer-esbuild` documentation](/docs/tools/metro-serializer-esbuild).
+
 ### Duplicate Dependencies
 
 Did you know that your app bundle can have multiple copies of a single package

packages/metro-serializer-esbuild/README.md

@@ -38,6 +38,54 @@ Native below 0.64.
 
 ## Usage
 
+If you use `react-native rnx-bundle`, enable tree shaking in your rnx-kit
+configuration:
+
+```json
+{
+  "rnx-kit": {
+    "bundle": {
+      "entryFile": "index.js",
+      "targets": ["android", "ios"],
+      "treeShake": true
+    }
+  }
+}
+```
+
+Then create a production bundle:
+
+```sh
+react-native rnx-bundle --platform ios --dev false
+```
+
+The `treeShake` property can also be an options object for this serializer:
+
+```json
+{
+  "rnx-kit": {
+    "bundle": {
+      "treeShake": {
+        "analyze": true,
+        "metafile": "dist/esbuild-meta.json",
+        "drop": ["debugger"]
+      }
+    }
+  }
+}
+```
+
+For one-off validation, use the command-line override:
+
+```sh
+react-native rnx-bundle --platform ios --dev false --tree-shake true
+```
+
+Tree shaking only runs for production bundles. If `--dev` is true, it is turned
+off even when `treeShake` is enabled.
+
+### Manual Metro Setup
+
 esbuild works best when we pass it ES6 modules. The first thing we must do is to
 disable import/export transformation by enabling `disableImportExportTransform`
 in `babel.config.js`:
@@ -99,6 +147,21 @@ We can now create a bundle as usual, e.g.:
 react-native bundle --entry-file index.js --platform ios --dev false ...
 ```
 
+## Checking the Result
+
+Build once without tree shaking and once with it, then compare bundle sizes:
+
+```sh
+react-native rnx-bundle --platform ios --dev false --tree-shake false
+mv index.ios.jsbundle index.ios.baseline.jsbundle
+
+react-native rnx-bundle --platform ios --dev false --tree-shake true
+ls -lh index.ios.baseline.jsbundle index.ios.jsbundle
+```
+
+For deeper inspection, enable `metafile` and load the generated JSON in an
+esbuild metafile analyzer.
+
 ## Options
 
 Similar to