Tor protocol errors causing silent dropped cells

While testing vanguards, I've got some mystery cases client side where circuits are getting closed with END_CIRC_REASON_TORPROTOCOL, but Tor is not emmitting any log lines that correspond to this, even at debug level.

This is happening for circuits with purpose CIRCUIT_PURPOSE_C_REND_READY_INTRO_ACKED. Additionally, all circuits seem able to fail during construction with END_CIRC_REASON_TORPROTOCOL, with no Tor log messages even at debug loglevel. Possibly more ntor handshake failures, similar to #29700 (moved)?

Finally, CIRCUIT_PURPOSE_C_INTRODUCE_ACKED circuits are getting closed with a END_CIRC_REASON_FINISHED after receiving an invalid cell, seemingly after they are done being used.

The vanguards addon now outputs this bug number at INFO log level when this happens.

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