T5.8: Tier G response policy — Verdict enum + ResponsePolicy + typed Hangup::PolicyViolation + 9 tests

crates/wzp-proto/src/packet.rs

@@ -1256,7 +1256,7 @@ pub fn default_signal_version() -> u8 {
     1
 }
 
-/// Reasons for ending a call.
+/// Typed reason for a call hangup.
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub enum HangupReason {
     Normal,
@@ -1269,6 +1269,30 @@ pub enum HangupReason {
         /// Versions the server is willing to speak.
         server_supported: Vec<u8>,
     },
+    /// Relay conformance policy violation (Tier G).
+    PolicyViolation {
+        /// Machine-readable violation code.
+        code: ViolationCode,
+        /// Human-readable explanation.
+        reason: String,
+    },
+}
+
+/// Machine-readable policy-violation codes.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum ViolationCode {
+    /// Tier A — sustained bitrate exceeded codec ceiling.
+    Bitrate,
+    /// Tier B — packet rate exceeded safety limit.
+    PacketRate,
+    /// Tier C — timestamp drift.
+    TimestampDrift,
+    /// Tier D — payload size anomaly.
+    PayloadSize,
+    /// Tier E — per-session rate cap.
+    RateCap,
+    /// Tier F — behavioural entropy score below threshold.
+    Entropy,
 }
 
 #[cfg(test)]

crates/wzp-relay/src/lib.rs

@@ -12,6 +12,7 @@ pub mod call_registry;
 pub mod config;
 pub mod audio_scorer;
 pub mod conformance;
+pub mod response_policy;
 pub mod event_log;
 pub mod federation;
 pub mod handshake;

crates/wzp-relay/src/response_policy.rs

@@ -0,0 +1,226 @@
+//! Tier G response policy — maps conformance verdicts to enforcement actions.
+//!
+//! Actions:
+//! - `Legitimate`    → no action
+//! - `Suspect`       → tighten Tier E quota, emit metric
+//! - `Abusive`       → typed Hangup + 1 h fingerprint cool-down
+//! - `RepeatAbusive` → relay-local block 24 h
+
+use std::collections::HashMap;
+use std::time::{Duration, Instant};
+
+use wzp_proto::packet::{HangupReason, ViolationCode};
+
+/// Conformance verdict produced by Tier F scoring.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum Verdict {
+    /// No suspicion.
+    Legitimate,
+    /// Tightened monitoring.
+    Suspect,
+    /// High confidence of abuse — close session.
+    Abusive,
+    /// Already abusive once in the last 24 h — escalate to block.
+    RepeatAbusive,
+}
+
+/// Enforcement action recommended by the response policy.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum Action {
+    /// Pass through unchanged.
+    Allow,
+    /// Throttle to tighter quota (Tier E).
+    Throttle,
+    /// Close the session with a typed Hangup signal.
+    Close { reason: HangupReason },
+    /// Block the fingerprint from joining any room for 24 h.
+    Block,
+}
+
+/// Tracks fingerprint-level abuse history and applies escalation.
+pub struct ResponsePolicy {
+    /// `(fingerprint, violation_code)` → last abusive instant.
+    cooldowns: HashMap<(String, ViolationCode), Instant>,
+    /// Cool-down duration for first-time abuse.
+    cooldown_duration: Duration,
+    /// Block duration for repeat abuse.
+    block_duration: Duration,
+}
+
+impl ResponsePolicy {
+    pub fn new() -> Self {
+        Self {
+            cooldowns: HashMap::new(),
+            cooldown_duration: Duration::from_secs(3600), // 1 h
+            block_duration: Duration::from_secs(86400),   // 24 h
+        }
+    }
+
+    /// Evaluate a verdict and produce the corresponding [`Action`].
+    ///
+    /// `fingerprint` is the participant's identity string (or IP as fallback).
+    /// `code` is the specific violation type that triggered the verdict.
+    pub fn evaluate(
+        &mut self,
+        fingerprint: &str,
+        code: ViolationCode,
+        verdict: Verdict,
+    ) -> Action {
+        match verdict {
+            Verdict::Legitimate => Action::Allow,
+            Verdict::Suspect => Action::Throttle,
+            Verdict::Abusive => {
+                let key = (fingerprint.to_string(), code);
+                let now = Instant::now();
+
+                // Check if this fingerprint was already abusive recently.
+                let is_repeat = self
+                    .cooldowns
+                    .get(&key)
+                    .map(|last| now.duration_since(*last) < self.block_duration)
+                    .unwrap_or(false);
+
+                if is_repeat {
+                    Action::Block
+                } else {
+                    self.cooldowns.insert(key, now);
+                    Action::Close {
+                        reason: HangupReason::PolicyViolation {
+                            code,
+                            reason: format!("Tier G enforcement: {code:?}"),
+                        },
+                    }
+                }
+            }
+            Verdict::RepeatAbusive => Action::Block,
+        }
+    }
+
+    /// Returns true if the fingerprint is currently blocked (repeat abuse).
+    pub fn is_blocked(&self, fingerprint: &str) -> bool {
+        let now = Instant::now();
+        self.cooldowns.iter().any(|((fp, _), last)| {
+            fp == fingerprint && now.duration_since(*last) < self.block_duration
+        })
+    }
+
+    /// Clean up expired cooldown entries.
+    pub fn prune(&mut self) {
+        let now = Instant::now();
+        self.cooldowns
+            .retain(|_, last| now.duration_since(*last) < self.block_duration);
+    }
+
+    /// Number of tracked cooldown entries.
+    pub fn len(&self) -> usize {
+        self.cooldowns.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.cooldowns.is_empty()
+    }
+}
+
+impl Default for ResponsePolicy {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn legitimate_allowed() {
+        let mut policy = ResponsePolicy::new();
+        assert_eq!(
+            policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Legitimate),
+            Action::Allow
+        );
+    }
+
+    #[test]
+    fn suspect_throttled() {
+        let mut policy = ResponsePolicy::new();
+        assert_eq!(
+            policy.evaluate("alice", ViolationCode::Entropy, Verdict::Suspect),
+            Action::Throttle
+        );
+    }
+
+    #[test]
+    fn abusive_gets_close() {
+        let mut policy = ResponsePolicy::new();
+        let action = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        assert!(
+            matches!(action, Action::Close { .. }),
+            "first-time abuse should close session"
+        );
+    }
+
+    #[test]
+    fn repeat_abusive_gets_block() {
+        let mut policy = ResponsePolicy::new();
+        // First abuse
+        let _ = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        // Second abuse within window → block
+        let action = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        assert_eq!(action, Action::Block, "repeat abuse should block");
+    }
+
+    #[test]
+    fn different_violation_codes_are_independent() {
+        let mut policy = ResponsePolicy::new();
+        // Abuse on bitrate
+        let _ = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        // Abuse on entropy is treated as first-time for that code
+        let action = policy.evaluate("alice", ViolationCode::Entropy, Verdict::Abusive);
+        assert!(
+            matches!(action, Action::Close { .. }),
+            "different violation code should not trigger repeat"
+        );
+    }
+
+    #[test]
+    fn is_blocked_true_after_repeat() {
+        let mut policy = ResponsePolicy::new();
+        let _ = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        let _ = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        assert!(policy.is_blocked("alice"));
+    }
+
+    #[test]
+    fn is_blocked_false_for_legitimate() {
+        let policy = ResponsePolicy::new();
+        assert!(!policy.is_blocked("alice"));
+    }
+
+    #[test]
+    fn prune_removes_expired() {
+        let mut policy = ResponsePolicy::new();
+        let _ = policy.evaluate("alice", ViolationCode::Bitrate, Verdict::Abusive);
+        assert_eq!(policy.len(), 1);
+        // Manually expire by moving cooldown back
+        policy
+            .cooldowns
+            .insert(("alice".to_string(), ViolationCode::Bitrate), Instant::now() - Duration::from_secs(90000));
+        policy.prune();
+        assert!(policy.is_empty());
+    }
+
+    #[test]
+    fn close_reason_contains_code() {
+        let mut policy = ResponsePolicy::new();
+        let action = policy.evaluate("alice", ViolationCode::Entropy, Verdict::Abusive);
+        match action {
+            Action::Close { reason } => match reason {
+                HangupReason::PolicyViolation { code, .. } => {
+                    assert_eq!(code, ViolationCode::Entropy);
+                }
+                other => panic!("expected PolicyViolation, got {other:?}"),
+            },
+            other => panic!("expected Close, got {other:?}"),
+        }
+    }
+}