EAS Observe rejects 7.47 MiB Gradle source map although Expo CLI Hermes map fits 5 MiB

## Build/Submit details page URL

Omitted from the public issue because the build belongs to a private project. I can provide the build URL and server request ID privately to Expo maintainers.

## Summary

With `uploadSourceMaps: true`, an otherwise successful Android EAS Build cannot upload its source map to EAS Observe because the processed Gradle-generated map is 7,836,304 bytes and the server rejects maps at 5 MiB. A production `expo export --platform android --source-maps external` for the same JavaScript produces a Hermes-composed map that is 5,059,651 bytes after removing `sourcesContent`, which is below the 5 MiB limit.

Expected: EAS Build uploads an equivalent source map that fits the server limit, supports a compact/compressed representation, or provides a supported way to select/process the map before upload.

Actual: the Android app bundle finishes successfully, but source-map upload fails and EAS Observe errors cannot be symbolicated.

## Managed or bare?

Managed / Continuous Native Generation. EAS runs `npx expo prebuild --clean`; the EAS job reports `type: managed`.

## Environment

```text
Local:
OS: Linux / WSL2
Node: 20.19.5
npm: 10.8.2
eas-cli: 23.2.0

Packages:
expo: 57.0.21
expo-observe: 57.0.20
expo-router: 57.0.20
expo-updates: 57.0.21
react: 19.2.3
react-native: 0.86.3
react-native-reanimated: 4.5.1
react-native-worklets: 0.10.1

EAS Build:
Platform: Android
Profile: preview
Build type: app-bundle
Node: 22.13.0
Image: ubuntu-26.04-jdk-17-ndk-r27b-sdk-57
NODE_ENV: production
BABEL_ENV: production

Expo Doctor:
21/21 checks passed. No issues detected.
```

## Error output

The Gradle build first creates the packager map:

```text
Writing sourcemap output to: /android/app/build/intermediates/sourcemaps/react/release/index.android.bundle.packager.map
```

During `UPLOAD_BUILD_ARTIFACTS`, EAS selects the generated map:

```text
Uploading source map: /android/app/build/generated/sourcemaps/react/release/index.android.bundle.map
Source map upload failed
size: 7836304
Unexpected response from server (400):
{"errors":[{"code":"VALIDATION_ERROR","type":"USER","message":"Source map size must be less than 5 MiB.","isTransient":false}]}
```

The build itself finishes successfully; only source-map upload is reported as a warning.

## Reproducible demo or steps to reproduce from a blank project

The exact EAS build URL and request ID can be shared privately with Expo maintainers.

1. Use an Expo SDK 57 managed/CNG app with a sufficiently large native JavaScript graph. The affected build bundled 4,499 modules. The largest dependency is `stream-chat-expo@9.3.0`, but the failure occurs in EAS source-map upload rather than Stream runtime code.
2. Install `expo-observe@57.0.20`.
3. Configure an EAS Android profile with production transforms and source-map upload:

```json
{
"build": {
"preview": {
"distribution": "internal",
"uploadSourceMaps": true,
"env": {
"NODE_ENV": "production",
"BABEL_ENV": "production"
},
"android": {
"buildType": "app-bundle"
}
}
}
}
```

4. Run `eas build --platform android --profile preview --clear-cache`.
5. Observe the 400 validation error during `UPLOAD_BUILD_ARTIFACTS` when the stripped map is larger than 5 MiB.

For comparison, generate the Expo CLI production export locally:

```sh
NODE_ENV=production BABEL_ENV=production npx expo export \
--platform android \
--source-maps external \
--clear
```

Parsing the resulting Android Hermes map, deleting only the top-level `sourcesContent` property, and serializing it with `JSON.stringify` gives:

```text
Raw Hermes map: 21,277,447 bytes
Without sourcesContent: 5,059,651 bytes (4.83 MiB)
5 MiB server limit: 5,242,880 bytes
```

The corresponding EAS Gradle-generated upload payload is 7,836,304 bytes (7.47 MiB). Could EAS use the smaller Expo CLI-equivalent Hermes map, further compact the Gradle map, accept gzip transfer/storage, or expose a supported preprocessing/upload path?

Trace the UPLOAD_BUILD_ARTIFACTS source-map selection and upload path in EAS CLI, using the reported Gradle-generated map and the Expo CLI Hermes map as comparison points. Determine how the selected map can stay within the EAS Observe limit or be processed through a supported path; done means the affected Android build uploads its map successfully and errors can be symbolicated.

Written by the indexing model from the issue text.