fix(android): reset readiness when the editor crashes

[dcalhoun]

What?

Android never cleared isEditorLoaded, so every guard built on it kept passing after the editor crashed.

Why?

isEditorLoaded is set once in onEditorLoaded and cleared nowhere — not on an editor crash, and not even on WebView process termination, which iOS does handle in controllerWebContentProcessDidTerminate.

So after the editor's ErrorBoundary unmounts the editor and deletes the window.editor.* methods, calls still reach a web view that can no longer answer them. This is the Android half of CMM-2008; #638 covers iOS and adds the onEditorUnavailable message this receives.

It also unblocks the host: GutenbergKitEditorFragment.editorReady has the same never-reset problem, and its updateFromEditor guard cannot start working until GutenbergKit tells it the editor is gone.

How?

• Receive onEditorUnavailable over the existing editorDelegate interface and clear isEditorLoaded.
• Add EditorUnavailableListener plus setEditorDidBecomeUnavailable, mirroring the existing EditorAvailableListener pattern, and clear it alongside the other listeners on teardown.

Relationship to #639

#639 fixes the consequence — one call site that turned a failed read into an empty title, which WordPress-Android persisted locally and then sent to the server. This PR fixes the cause, so the call is not made at all. They are independent and worth having both: #639 protects any host on today's release without a host change, this one stops the whole class.

Both touch GutenbergView.kt but in different regions, so they should rebase cleanly in either order.

Not included

• didFireEditorLoaded is deliberately untouched. It guards the available listener against firing twice, and changing it would alter reload behaviour that has no reload path yet.
• Host-side work — resetting GutenbergKitEditorFragment.editorReady and disabling the controls that no longer function — is a separate WordPress-Android change.

Testing Instructions

Unit tests: ./android/gradlew -p ./android :Gutenberg:testDebugUnitTest --tests "org.wordpress.gutenberg.GutenbergViewTest"

Two tests cover this. Note the second asserts that no JavaScript reaches the web view rather than asserting on the callback — Robolectric's shadow WebView never invokes the ValueCallback, so a callback-based assertion passes with or without the fix. I verified the committed version fails when the reset is removed.

Manually, in the demo app:

1. Open the editor and trip the boundary from chrome://inspect:

   const be = wp.data.select( 'core/block-editor' );
   be.getBlockOrder = () => { throw new Error( 'repro' ); };
   wp.data.dispatch( 'core/block-editor' ).updateSettings( {} );

2. adb logcat | grep GutenbergView shows EditorUnavailable received in native code.
3. Confirm normal editing, undo/redo and saving still work without a crash.

Accessibility Testing Instructions

N/A — no UI changes.

Screenshots or screencast

N/A

🤖 Generated with Claude Code

https://claude.ai/code/session_01VuxMbKtUsaUF8nUVgKdxwK

[wpmobilebot]

XCFramework Build

This PR's XCFramework is available for testing. Add the following to your Package.swift:

.package(url: "https://github.com/wordpress-mobile/GutenbergKit", branch: "pr-build/640")

_{Built from 383662b}