Handle Node serial transport disconnects as status events

[Copilot]

Description

build-and-package was failing on a single transport-node-serial contract test: an underlying serial-port error was escaping as a fatal stream error instead of being surfaced as a disconnect status. This change aligns serial transport behavior with the existing Node socket transport so link drops are reported as DeviceDisconnected events.

Related Issues

N/A

Changes Made

• Transport error handling

  • Track terminal port error state in TransportNodeSerial
  • On serial error, tear down the port and emit DeviceDisconnected("port-error")
  • Treat read-loop termination after a port error as graceful stream closure instead of propagating a public read failure

• Disconnect signal consistency

  • Suppress follow-on write-pipe disconnect handling once the port is already marked errored
  • Keep disconnect semantics consistent with packages/transport-node/src/transport.ts

• Regression coverage

  • Add a focused test for the port-error path to verify consumers observe a disconnect status event

this.port.on("error", (err) => {
  this.errored = true;
  this.port?.removeAllListeners();
  this.port?.destroy();

  if (!this.closingByUser) {
    this.emitStatus(DeviceStatusEnum.DeviceDisconnected, "port-error");
  }
});

Testing Done

Added targeted regression coverage for the serial-port error disconnect path in packages/transport-node-serial/src/transport.test.ts.

Screenshots (if applicable)

N/A

Checklist

• Code follows project style guidelines
• Documentation has been updated or added
• Tests have been added or updated
• All i18n translation labels have been added (read
  CONTRIBUTING_I18N_DEVELOPER_GUIDE.md for more details)

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Project	Deployment	Actions	Updated
web-test	Ready	Preview	Sep 10, 2026 9:15pm UTC

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[danditomaso]

Thanks for the PR. Fundamentally I'm always against error booleans because it makes impossible states possible. A better approach is to expand the enum to include the generic error and base the UI on that.

Impossible state would be something like:
{
hasErrored:true
statusEnum: "success"

}