feat(quote): downscore peers that supply bad-bound quotes

[grumbach]

Summary

• When a peer's storage quote ships a pub_key that does not BLAKE3-hash to the peer's claimed PeerId, report a strong negative trust event so the local AdaptiveDHT swaps that peer out of the routing table on the next admission cycle. This stops the operator-monopolises-close-K failure mode that took uploads below quorum on 2026-05-06.
• Wires the report at both detection sites in ant-core/src/data/client/quote.rs:
  • per-peer classify_quote_response (primary defence inside the async closure) — fires for every BadQuoteBinding verdict;
  • post-collection drop_quotes_with_bad_bindings (defensive filter) — fires for every peer whose quote slipped past the per-peer handler.
• Both sites go through a small TrustReporter trait so the wiring can be unit-tested with a mock recorder rather than a live P2PNode. Production paths use the blanket impl on Arc<P2PNode> which forwards to P2PNode::report_application_failure(peer, 5.0).
• The 5.0 weight is sized to drop a peer from neutral 0.5 to ~0.26 in a single event, well below the production swap-out threshold (saorsa_core::adaptive::DEFAULT_SWAP_THRESHOLD = 0.35). saorsa-core clamps consumer weights at MAX_CONSUMER_WEIGHT = 5.0 so this is the strongest legal signal — appropriate for a verifiable cryptographic mismatch.
• See notes/plan-1-bad-node-eviction.md for the full design and the production failure that motivates this work.

What's new in tests

• classify_quote_response_reports_trust_event_on_bad_binding (B1)
• classify_quote_response_does_not_report_on_good_binding
• classify_quote_response_does_not_report_on_non_binding_failures
• drop_quotes_with_bad_bindings_reports_one_event_per_dropped_peer (B2)
• bad_binding_does_not_affect_trust_for_other_peers (B3)

Existing tests for drop_quotes_with_bad_bindings are updated for the new return type (Vec<PeerId> rather than usize count) so the caller can attribute trust events per peer.

Test plan

• cargo test -p ant-core --lib data::client::quote (25/25 pass)
• cargo clippy -p ant-core --lib -- -D warnings
• cargo fmt --all -- --check

Dependencies

• feat(adaptive): downscore peers via P2PNode::report_application_failure saorsa-labs/saorsa-core#114 — adds P2PNode::report_application_failure. This PR's CI will fail until that lands and the saorsa-core git pin is updated.

Cross-links

• saorsa-core PR: feat(adaptive): downscore peers via P2PNode::report_application_failure saorsa-labs/saorsa-core#114
• ant-node PR: docs(payment): document storer-side bad-binding rejection + add regression tests ant-node#90

Behaviour-preservation argument

• Why this is safe: trust events are advisory; the 0.35 swap threshold is already the production knob. We are emitting a stronger negative signal for strictly stronger evidence — a verifiable cryptographic mismatch is more conclusive than a dial timeout.
• NAT-safe: trust is per-PeerId, not per-IP. Legitimate peers behind a shared NAT are unaffected.
• No false-positive risk for honest peers: the score decays back above the swap threshold in ~1 day, so a peer that fixes a temporary mis-sign re-enters the lookup pool naturally.
• Sybil resistance preserved: the eviction makes crossed-key Sybils less effective, not more — the same attacker now has to spin up new identities at a higher rate to keep occupying close-K slots.