Detect incompatible WebView engines before extension startup and provide inline recovery #68

Found during #65 / PR #66's emulator-only production-readiness pass. Related to #7.

The exact candidate APK 409088cb9879507454598038ea4f7dd3bc54a40a0facee48c376f95152f9908e (implementation 944aca80afbddd042d937058d649b01aa92fcc6c) installs and launches on the API26 ARM64 Google APIs image revision3. Its WebView provider is com.google.android.webview version 58.0.3029.125.

A two-item React/List fixture never publishes its native rows. Device Chromium logs report Uncaught SyntaxError: Unexpected token . and Unexpected token { while evaluating the unchanged adapter/runtime. The runtime has optional chaining/null-coalescing and modern APIs, while the host evaluates assets before it has a reliable capability failure path. A dedicated diagnostic records the native UI error as ReferenceError: __tinycast is not defined, with no rendered fixture row. The List test’s row wait times out; that is distinct from an app watchdog timeout. The existing desktop-API watchdog is not established as the result of this particular reproduction. This is a runtime compatibility finding, separate from API26 test-helper failures involving capture/clipboard APIs.

Acceptance criteria:

• Probe required parser syntax and runtime APIs before evaluating the unchanged vendored assets, using a probe that itself runs on legacy engines.
• Reject an incompatible engine promptly, naming the actual provider/version and giving specific WebView/Chrome update guidance inside the palette. Preserve native Back/Close and caller state, and prevent extension dispatch while blocked.
• Provide native recovery without forwarding extension-controlled intents or opening another app automatically.
• Demonstrate the actual old-engine path on API26 and normal List/Grid execution on a modern engine; include real Android before/after/error screenshots and exact binary/provider identities.
• Preserve all vendored assets/notices unchanged and obtain two independent sol6.1/high audits.
• Keep actual Android8 extension execution partial until tested with an adequate updated provider or a maintained embedded engine. A readable rejection is not extension-execution parity, a security certification, or production clearance.

Original failed runs and Chromium logs remain retained. Host screenshot/capture failures and API assumptions do not become passes because the compatibility problem is now identified.

The diagnostic also recorded a successful UiAutomation screenshot and a successful shell screencap at the AVD’s physical1080×1920 viewport. Earlier forced2340px capture failures are retained separately; a geometry relationship is under investigation, not an established cause.