Android AppFunctions are indexed/enabled on device but Gemini cannot resolve custom function metadata

## Description of the bug
I integrated [Android AppFunctions](https://developer.android.com/ai/appfunctions) in a third-party app and verified that the platform indexes and enables all functions. However, Gemini does not discover or execute these functions and logs metadata resolution failures.

### Environment
- Device: Samsung Galaxy A34 (`SM-A346B`)
- Android: 16 (`SDK 36`)
- Build tools: AGP `8.9.1`, Gradle `8.14.3`
- Language/tooling: Kotlin `2.1.10`, KSP `2.1.10-1.0.31`
- Libraries:
- `androidx.appfunctions:appfunctions:1.0.0-alpha07`
- `androidx.appfunctions:appfunctions-service:1.0.0-alpha07`
- `androidx.appfunctions:appfunctions-compiler:1.0.0-alpha07`

### What was validated already
- KSP aggregation is enabled: `appfunctions:aggregateAppFunctions=true`
- APK includes required assets:
- `assets/app_functions.xml`
- `assets/app_functions_v2.xml`
- `assets/app_functions_schema.xsd`
- Manifest contains merged AppFunction services/properties.
- Device has `com.android.extensions.appfunctions` library.
- `dumpsys app_function` shows all six functions with runtime metadata and `enabled: [1]`.
- App-side diagnostics report `6/6 functions indexed`.

### Minimal reproduction
1. Build and install app on Android 16 device.
2. Launch app and wait for AppFunction registration/indexing.
3. Confirm indexed state via `dumpsys app_function` and app logs.
4. Attempt discovery/execution through Gemini.

## Actual vs expected behavior
### Actual behavior
- Gemini does not discover/execute the custom app functions.
- Logs repeatedly show: `D/AppFunctions: Unable to resolve AppFunctionMetadata.`

### Expected behavior
- Once functions are indexed and enabled by the Android AppFunctions platform, Gemini should discover and be able to execute them, or provide a clear compatibility reason if custom schemas are unsupported.

## Any other information you'd like to share?
- This may be a support/compatibility question rather than a pure runtime bug.
- If custom app-defined schemas are not currently supported in Gemini, please confirm current limitations and any roadmap for support.

No repository file or test is named in the report. Start with the Android AppFunctions documentation and the minimal reproduction, then inspect `dumpsys app_function` and the reported `Unable to resolve AppFunctionMetadata` log. Done means establishing whether Gemini supports these custom schemas and documenting a confirmed compatibility limitation or actionable repository change.

Written by the indexing model from the issue text.