test(#1611): Android emulator instrumented tests for the Kotlin exact-ref model host (Spec 138 0.13.1)

[enricopiovesan]

Summary

Closes the gap Decision 108 left open: the Kotlin exact-ref model host now runs on a real Android runtime in CI, not only on the host-JVM build of traverse-android-host.

• New android-emulator-tests CI job (ubuntu-latest, KVM):

  • cross-builds traverse-android-host with cargo-ndk (the AAR's arm64-v8a/x86_64 libraries, export and 16 KiB-page checks included);
  • boots an x86_64 API 34 google_apis emulator with reactivecircus/android-emulator-runner;
  • runs connectedDebugAndroidTest.

  Flakiness is mitigated with a cached AVD and boot snapshot (actions/cache), -no-snapshot-save for a clean state, a headless emulator with animations disabled, the Orchestrator, and test reports uploaded on failure. The timeout is 45 minutes.

• ExactModelHostInstrumentedTest (androidTest) loads traverse_android_host through System.loadLibrary from jniLibs, as an app does. It covers:

  • the signed vectors byte-for-byte: classifier, digits-mlp, digits-onnx (+simd128), and prepared-v3 over 3 rounds (fresh, then snapshot);
  • the shared 21-case rights suite, with JSON equality on codes, reasons, details and evidence;
  • missingNativeLibraryFailsClosed: pointing the loader at a nonexistent library, before ExactModelNative initialises, fails the load as a stripped .so would, so every model call gives model_unavailable / engine_unavailable.

  The fixtures are fixtures/models, bundled as test-APK assets.

• Android Test Orchestrator with clearPackageData, so every test runs in its own process and the forced load failure can't leak into the others.

• Docs: docs/android-emulator-tests.md covers what runs, the runtime, the flakiness mitigations, and how to run it locally.

• Spec 138 0.13.0 → 0.13.1 amends FR-048, whose text said the host-JVM build was used "until Android-emulator coverage lands (Android emulator instrumented tests for Kotlin exact-ref model execution (Decision 108 follow-up) #1611)". Testing only; no behaviour change.

Governing Spec

• 138-governed-exact-model-execution
• 068-public-platform-embedder-packages
• 031-supply-chain-hardening
• 060-wasm-resource-limits
• 004-spec-alignment-gate

Project Item

• Closes Android emulator instrumented tests for Kotlin exact-ref model execution (Decision 108 follow-up) #1611 (Project 1).

Validation

• This machine has no JDK or Android SDK, so the instrumented tests and the emulator job are verified by this PR's CI (android-emulator-tests). The test logic is a port of the passing host-JVM ExactModelHostTest (same vectors, same suite assertions); only the fixture source (APK assets) and the library loading differ.
• The workflow YAML parses. spec_alignment_check.sh and pr_body_check.sh pass.
• No Rust or runtime code changed. Every new fixture referenced (conformance/signed-prepared-v3.json, rights-conformance/) is already on main.

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