Add onMediaError instance method

[captbaritone]

When a track can't be fetched or decoded, ElementSource logs the error, then triggers ended and sets the status to STOPPED. That keeps Webamp from getting stuck, but it means an embedder can't tell an undecodable file from the end of a track. agentcloud currently works around this by probing the same URL with a hidden <audio> element.

This adds a public signal:

const unsubscribe = webamp.onMediaError(({ code }) => {
  if (code === MediaError.MEDIA_ERR_SRC_NOT_SUPPORTED) {
    showUnsupportedFileMessage();
  }
});

code is the underlying MediaError.code. It's passed in an object so more fields can be added later without breaking callers.

Implementation

• ElementSource emits "error" with the code, just before its existing "ended".
• Media re-emits it, and the media middleware dispatches a new MEDIA_ERROR action.
• onMediaError subscribes to that action, the same way onClose/onMinimize do.
• Behavior is otherwise unchanged. The error is still logged, and Webamp still continues as if the track ended. Embedders get onMediaError before the resulting track change.

Documented in the instance methods docs.

Testing

• New onMediaError.test.ts constructs a real WebampLazy with a fake media class via the existing __customMediaClass option, emits "error", and checks that the callback gets { code } and that unsubscribing works.
• tsc, eslint, prettier --check and vitest run pass locally.

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[github-actions]

Size Change: +132 B (+0.03%)

Total Size: 490 kB

📦 View Changed

Filename	Size	Change
packages/webamp/built/webamp.bundle.min.js	298 kB	+71 B (+0.02%)
packages/webamp/built/webamp.lazy-bundle.min.js	192 kB	+61 B (+0.03%)

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