Subscriber loses App reset codes and returns Transport(Cancel) error instead of Error::App(code)

[roberte777]

Summary

When a publisher aborts with an application error, the subscriber receives Error::Transport(Cancel) instead of Error::App(code).

Publisher side:

self.track_producer.abort(MoqError::App(code));

This triggers a stream reset with the MoQ error code, but the subscriber path does not preserve/decode it into Error::App.

Expected behavior

If peer sends a reset/close code corresponding to MoQ app error (64 + app_code), subscriber should surface:

• MoqError::App(app_code) for app-defined codes
• mapped built-in MoQ errors for known protocol codes (where applicable)
• fallback to MoqError::Transport only when code is unknown/unavailable

[coderabbitai]

🔗 Related PRs

#615 - Use MaybeSend and MaybeSync for WASM compatibility [merged]
#669 - IETF: Don't return an error when the control stream is closed. [merged]
#670 - IETF: Use the correct error message. [merged]

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