[tor-project] Tor's history of D/DoS attacks; strategy for mitigation

I'm investigating the applicability of the IETF's DDoS Open Threat Signaling (DOTS) specifications[1] to the needs of privacy-preserving overlay networks, including VPNs but with particular interest in Tor.

Specifically, now that the July 2022 D/DoS attack has finally come to a close, I'm wondering about:

1. the history, frequency, and magnitude of D/DoS attacks against the Tor network;

2. when these have taken the form of Tor traffic versus lower-level attacks on Tor nodes and HSDirs; and

3. how the new "proof of work over introduction circuits" scheme fits into Tor's overall strategy for mitigating D/DoS attacks.

I've found plenty of current and historical GitLab tickets---but I'm wondering if there are more comprehensive documents or other resources I'm not aware of.

--- cfm[2].

[1]: https://datatracker.ietf.org/wg/dots/documents/

[2]: I'm a maintainer of the SecureDrop project at the Freedom of the Press Foundation, but this work is supported by ARTICLE 19's Internet of Rights Fellowship.