Resurrect dead Noise vector tests; add CI perf floors; make tests hermetic

Package.swift's .process("Noise") resource claim silently excluded all
of bitchatTests/Noise/ from compilation since Oct 2025 - including a
complete official-vector runner (cacophony + snow XX transcripts,
transport messages, handshake hash, byte-identical to upstream).
Narrowing the resource to the JSON file and loading via Bundle.module
brings 51 Noise tests back to life, with a guard asserting each
vector's protocol name matches the app's.

CI gains a performance floor gate: perf-floors.json carries deliberately
generous floors (~25% of measured throughput) that catch algorithmic
regressions without flaking on runner variance; PERF lines reach the
gate via an O_APPEND side-channel file since swift test --parallel
swallows passing tests' stdout.

Tests are now hermetic: FavoritesPersistenceService uses an in-memory
keychain under test (fixes the securityd hang that blocked pipeline
benchmarks locally) and read-receipt persistence uses a wiped scratch
UserDefaults suite instead of .standard.

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

bitchatTests/Performance/PerformanceBaselineTests.swift

@@ -38,15 +38,40 @@ final class PerformanceBaselineTests: XCTestCase {
     }
 
     /// Reports one human-readable throughput line per benchmark so CI logs
-    /// are readable without parsing XCTest's measure output.
+    /// are readable without parsing XCTest's measure output. The same line is
+    /// appended to the file named by `BITCHAT_PERF_LOG` (if set): under
+    /// `swift test --parallel` the runner swallows stdout of passing tests,
+    /// so the CI floor gate (scripts/check-perf-floors.sh) reads the file.
     private func reportThroughput(_ name: String, samples: [TimeInterval], operations: Int, unit: String) {
         guard !samples.isEmpty else { return }
         let avg = samples.reduce(0, +) / Double(samples.count)
         let opsPerSec = avg > 0 ? Double(operations) / avg : .infinity
-        print(String(
+        let line = String(
             format: "PERF[%@]: %.0f %@/sec (avg %.3f ms per pass of %d, %d passes)",
             name, opsPerSec, unit, avg * 1000, operations, samples.count
-        ))
+        )
+        print(line)
+        Self.appendToPerfLog(line)
+    }
+
+    private static var perfLogPath: String? {
+        let path = ProcessInfo.processInfo.environment["BITCHAT_PERF_LOG"]
+        return (path?.isEmpty ?? true) ? nil : path
+    }
+
+    /// Appends with `O_APPEND` because `swift test --parallel` may split this
+    /// class across worker processes that write concurrently. The file is
+    /// append-only (CI workspaces start fresh); delete it between local runs
+    /// if you reuse a path.
+    private static func appendToPerfLog(_ line: String) {
+        guard let path = perfLogPath else { return }
+        let fd = open(path, O_WRONLY | O_APPEND | O_CREAT, 0o644)
+        guard fd >= 0 else { return }
+        defer { close(fd) }
+        let bytes = Array((line + "\n").utf8)
+        bytes.withUnsafeBufferPointer { buffer in
+            _ = write(fd, buffer.baseAddress, buffer.count)
+        }
     }
 
     // MARK: - 1a. Nostr inbound event handling (fresh events)