Add regression and security tests for relay quota and TLS stream handling

- Introduced regression tests for relay quota wake liveness to ensure proper handling of contention and wake events.
- Added adversarial tests to validate the behavior of the quota system under stress and contention scenarios.
- Implemented security tests for the TLS stream to verify the preservation of pending plaintext during state transitions.
- Enhanced the pool writer tests to ensure proper quarantine behavior and validate the removal of writers from the registry.
- Included fuzz testing to assess the robustness of the quota and TLS handling mechanisms against unexpected inputs and states.

src/proxy/tests/client_beobachten_ttl_bounds_security_tests.rs

@@ -0,0 +1,126 @@
+use super::*;
+
+const BEOBACHTEN_TTL_MAX_MINUTES: u64 = 24 * 60;
+
+#[test]
+fn beobachten_ttl_exact_upper_bound_is_preserved() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+    config.general.beobachten_minutes = BEOBACHTEN_TTL_MAX_MINUTES;
+
+    let ttl = beobachten_ttl(&config);
+    assert_eq!(
+        ttl,
+        Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60),
+        "upper-bound TTL should remain unchanged"
+    );
+}
+
+#[test]
+fn beobachten_ttl_above_upper_bound_is_clamped() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+    config.general.beobachten_minutes = BEOBACHTEN_TTL_MAX_MINUTES + 1;
+
+    let ttl = beobachten_ttl(&config);
+    assert_eq!(
+        ttl,
+        Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60),
+        "TTL above security cap must be clamped"
+    );
+}
+
+#[test]
+fn beobachten_ttl_u64_max_is_clamped_fail_safe() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+    config.general.beobachten_minutes = u64::MAX;
+
+    let ttl = beobachten_ttl(&config);
+    assert_eq!(
+        ttl,
+        Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60),
+        "extreme configured TTL must not become multi-century retention"
+    );
+}
+
+#[test]
+fn positive_one_minute_maps_to_exact_60_seconds() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+    config.general.beobachten_minutes = 1;
+
+    assert_eq!(beobachten_ttl(&config), Duration::from_secs(60));
+}
+
+#[test]
+fn adversarial_boundary_triplet_behaves_deterministically() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+
+    config.general.beobachten_minutes = BEOBACHTEN_TTL_MAX_MINUTES - 1;
+    assert_eq!(
+        beobachten_ttl(&config),
+        Duration::from_secs((BEOBACHTEN_TTL_MAX_MINUTES - 1) * 60)
+    );
+
+    config.general.beobachten_minutes = BEOBACHTEN_TTL_MAX_MINUTES;
+    assert_eq!(
+        beobachten_ttl(&config),
+        Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60)
+    );
+
+    config.general.beobachten_minutes = BEOBACHTEN_TTL_MAX_MINUTES + 1;
+    assert_eq!(
+        beobachten_ttl(&config),
+        Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60)
+    );
+}
+
+#[test]
+fn light_fuzz_random_minutes_match_fail_safe_model() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+
+    let mut seed = 0xD15E_A5E5_F00D_BAADu64;
+    for _ in 0..8192 {
+        seed ^= seed << 7;
+        seed ^= seed >> 9;
+        seed ^= seed << 8;
+
+        config.general.beobachten_minutes = seed;
+        let ttl = beobachten_ttl(&config);
+        let expected = if seed == 0 {
+            Duration::from_secs(60)
+        } else {
+            Duration::from_secs(seed.min(BEOBACHTEN_TTL_MAX_MINUTES) * 60)
+        };
+
+        assert_eq!(ttl, expected, "ttl mismatch for minutes={seed}");
+        assert!(ttl <= Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60));
+    }
+}
+
+#[test]
+fn stress_monotonic_minutes_remain_monotonic_until_cap_then_flat() {
+    let mut config = ProxyConfig::default();
+    config.general.beobachten = true;
+
+    let mut prev = Duration::from_secs(0);
+    for minutes in 0..=(BEOBACHTEN_TTL_MAX_MINUTES + 4096) {
+        config.general.beobachten_minutes = minutes;
+        let ttl = beobachten_ttl(&config);
+
+        assert!(ttl >= prev, "ttl must be non-decreasing as minutes grow");
+        assert!(ttl <= Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60));
+
+        if minutes > BEOBACHTEN_TTL_MAX_MINUTES {
+            assert_eq!(
+                ttl,
+                Duration::from_secs(BEOBACHTEN_TTL_MAX_MINUTES * 60),
+                "ttl must stay clamped once cap is exceeded"
+            );
+        }
+        prev = ttl;
+    }
+}