Add runtime Tor-egress self-check (fail-closed) for Nostr relays

Runtime-verified whether Apple's URLSession honors connectionProxyDictionary
SOCKS settings for Nostr relay traffic (plain HTTPS + URLSessionWebSocketTask),
since the app routes all Nostr traffic through Arti's local SOCKS5 proxy solely
via those keys and Apple does not officially support SOCKS for URLSession on iOS.

Verification harness (scripts/tor-egress-verification/): a minimal SOCKS5 CONNECT
proxy that logs arriving connections, plus a Swift probe that runs an HTTPS GET
and a WebSocket ping through a URLSession configured with the proxy dict. Result:
on macOS (kCFNetworkProxiesSOCKS* constants) and the iOS simulator (raw
"SOCKSProxy"/"SOCKSPort" string keys, the exact app path) BOTH HTTP and WebSocket
are proxied, do remote DNS through the proxy, and the proxied session is
fail-closed (every request errors when the SOCKS proxy is down). The feared
direct-egress leak did not reproduce on the tested platforms.

Defense-in-depth for the platform Apple does not guarantee (physical iOS):
add TorEgressVerifier, which performs a canary request through the proxied
session and asserts the exit is a Tor node (check.torproject.org IsTor==true),
positively detecting a direct egress even if the OS silently ignored the proxy.
Policy: verifiedTor allows (cached for a TTL); notTor refuses (leak detected,
never open relays); unreachable allows-with-warning (session stays fail-closed
by construction). Wired into TorManager.awaitEgressReady() and required by both
NostrRelayManager and GeoRelayDirectory before opening connections. Cache is
invalidated on Tor restart/dormant/shutdown. Never falls back to a direct
connection.

Probe is injected so the policy/caching is unit-tested offline; the live-network
harness lives under scripts/ and is not run by CI.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

bitchatTests/Nostr/TorEgressVerifierTests.swift

@@ -0,0 +1,137 @@
+//
+// TorEgressVerifierTests.swift
+// bitchatTests
+//
+// Unit tests for the runtime Tor-egress self-check policy/caching. The network
+// probe is injected, so these tests are deterministic and offline.
+//
+
+import Testing
+import Foundation
+@testable import bitchat
+import Tor
+
+@Suite(.serialized)
+struct TorEgressVerifierTests {
+
+    /// Deterministic, controllable clock + probe.
+    private final class Harness: @unchecked Sendable {
+        private let lock = NSLock()
+        private var _now = Date(timeIntervalSince1970: 1_000_000)
+        private var _result: TorEgressVerifier.ProbeResult = .verifiedTor
+        private(set) var probeCount = 0
+
+        var now: Date {
+            lock.lock(); defer { lock.unlock() }; return _now
+        }
+        func advance(_ seconds: TimeInterval) {
+            lock.lock(); _now = _now.addingTimeInterval(seconds); lock.unlock()
+        }
+        func setResult(_ r: TorEgressVerifier.ProbeResult) {
+            lock.lock(); _result = r; lock.unlock()
+        }
+        func makeProbe() -> @Sendable () async -> TorEgressVerifier.ProbeResult {
+            return { [self] in
+                lock.lock(); probeCount += 1; let r = _result; lock.unlock()
+                return r
+            }
+        }
+        func nowProvider() -> @Sendable () -> Date {
+            return { [self] in self.now }
+        }
+    }
+
+    private func makeVerifier(_ h: Harness, ttl: TimeInterval = 300, minRetry: TimeInterval = 5) -> TorEgressVerifier {
+        TorEgressVerifier(ttl: ttl, minRetryInterval: minRetry, now: h.nowProvider(), probe: h.makeProbe())
+    }
+
+    @Test("verifiedTor allows and is cached within TTL (single probe)")
+    func verifiedIsCached() async {
+        let h = Harness()
+        h.setResult(.verifiedTor)
+        let v = makeVerifier(h, ttl: 300)
+
+        #expect(await v.verify() == true)
+        // Second call within TTL must not re-probe.
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 1)
+    }
+
+    @Test("cache expires after TTL and re-probes")
+    func cacheExpires() async {
+        let h = Harness()
+        h.setResult(.verifiedTor)
+        let v = makeVerifier(h, ttl: 300)
+
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 1)
+
+        h.advance(301)
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 2)
+    }
+
+    @Test("notTor refuses (leak detected) and is never cached as allowed")
+    func notTorRefuses() async {
+        let h = Harness()
+        h.setResult(.notTor)
+        let v = makeVerifier(h, ttl: 300, minRetry: 0)
+
+        #expect(await v.verify() == false)
+        // A subsequent success recovers.
+        h.setResult(.verifiedTor)
+        #expect(await v.verify() == true)
+    }
+
+    @Test("unreachable allows (session stays fail-closed) but does not cache a Tor verification")
+    func unreachableAllowsButNotCached() async {
+        let h = Harness()
+        h.setResult(.unreachable("down"))
+        let v = makeVerifier(h, ttl: 300, minRetry: 0)
+
+        #expect(await v.verify() == true)
+        // Not a verified state: once it turns into a real leak, we must refuse.
+        h.setResult(.notTor)
+        #expect(await v.verify() == false)
+    }
+
+    @Test("minRetryInterval throttles re-probing when not verified")
+    func throttleReprobe() async {
+        let h = Harness()
+        h.setResult(.unreachable("down"))
+        let v = makeVerifier(h, ttl: 300, minRetry: 5)
+
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 1)
+        // Within minRetry window: reuse last decision, no new probe.
+        h.advance(1)
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 1)
+        // After the window: re-probe.
+        h.advance(5)
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 2)
+    }
+
+    @Test("invalidate forces a fresh probe")
+    func invalidateForcesReprobe() async {
+        let h = Harness()
+        h.setResult(.verifiedTor)
+        let v = makeVerifier(h, ttl: 300)
+
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 1)
+        await v.invalidate()
+        #expect(await v.verify() == true)
+        #expect(h.probeCount == 2)
+    }
+
+    @Test("lastProbeResult reflects the most recent outcome")
+    func lastResultTracked() async {
+        let h = Harness()
+        h.setResult(.notTor)
+        let v = makeVerifier(h, ttl: 300, minRetry: 0)
+        _ = await v.verify()
+        #expect(await v.lastProbeResult() == .notTor)
+    }
+}