[AZ-585] [AZ-586] ResLim+Perf NFT tests; close test cycle 1

Batch 4 of test implementation cycle 1 (existing-code Step 6, final batch).

- AZ-585 SteadyStateLoadTests + ColdStartRssTests: NFT-RES-LIM-01..04.
  SteadyStateLoadFixture runs one 5-min sustained-load window and samples
  RSS (docker stats), Npgsql conns (pg_stat_activity), and FDs
  (/proc/1/fd) every 5s; three test methods assert independently. All
  SkippableFact-gated on docker primitives.
- AZ-586 PerformanceTests: NFT-PERF-01..04. Sequential single-client,
  5 warm-ups + N measured calls, P50+P95 via LatencyPercentiles, recorded
  to PERF_RESULTS_FILE. Tagged Category=Perf so default gate excludes them.

Infrastructure:
- entrypoint.sh now applies --filter "${TEST_FILTER:-Category!=Perf}"
  per AZ-586 (default CI gate excludes performance).
- MetricCsvRecorder: idempotent CSV appender keyed on env var, used by
  both Perf and ResLim categories.

Step 6 (Implement Tests) is complete. Final report at
_docs/03_implementation/implementation_report_tests.md handoffs the
full-suite gate to test-run/SKILL.md (Step 7).

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/Azaion.Missions.E2E.Tests/Helpers/MetricCsvRecorder.cs

@@ -0,0 +1,58 @@
+using System.Globalization;
+
+namespace Azaion.Missions.E2E.Helpers;
+
+/// <summary>
+/// Appends one row per NFT-PERF / NFT-RES-LIM scenario to a side-channel
+/// CSV referenced by an environment variable. The Reporting.Cli converter
+/// only knows about compile-time <c>[Trait]</c> data — runtime measurements
+/// (P50/P95, MAX_FD, P95_RSS_MiB, etc.) need this separate file so
+/// deployment planning + trend dashboards can read them.
+/// </summary>
+/// <remarks>
+/// File schema (idempotent header written on first append):
+/// <code>Timestamp,Category,Scenario,Result,Traces,ErrorMessage</code>
+/// The Traces column carries the dynamic key=value pairs the spec requires
+/// (e.g., <c>"AC-3.6; P50_MS=23.4; P95_MS=41.8"</c>); the recorder just
+/// joins them with semicolons — callers compose the right shape.
+/// </remarks>
+public sealed class MetricCsvRecorder
+{
+    private readonly string? _path;
+    private static readonly object Lock = new();
+
+    /// <param name="envVar">name of the env var that carries the target CSV path
+    /// (e.g., <c>PERF_RESULTS_FILE</c> for NFT-PERF, <c>RESLIM_RESULTS_FILE</c>
+    /// for NFT-RES-LIM). When the env var is missing or whitespace, every
+    /// <see cref="Record"/> call is a no-op — the recorder is intentionally
+    /// silent inside the standard CI run.</param>
+    public MetricCsvRecorder(string envVar)
+    {
+        var v = Environment.GetEnvironmentVariable(envVar);
+        _path = string.IsNullOrWhiteSpace(v) ? null : v;
+    }
+
+    public bool IsEnabled => _path is not null;
+
+    public void Record(string category, string scenario, string result, string traces, string? errorMessage = null)
+    {
+        if (_path is null) return;
+        lock (Lock)
+        {
+            var dir = Path.GetDirectoryName(_path);
+            if (!string.IsNullOrEmpty(dir)) Directory.CreateDirectory(dir);
+            var newFile = !File.Exists(_path);
+            using var sw = new StreamWriter(_path, append: true);
+            if (newFile)
+                sw.WriteLine("Timestamp,Category,Scenario,Result,Traces,ErrorMessage");
+            sw.WriteLine(
+                $"{DateTime.UtcNow.ToString("O", CultureInfo.InvariantCulture)},"
+                + $"{Csv(category)},{Csv(scenario)},{Csv(result)},{Csv(traces)},{Csv(errorMessage ?? "")}");
+        }
+    }
+
+    private static string Csv(string value) =>
+        value.Contains(',') || value.Contains('"') || value.Contains('\n')
+            ? "\"" + value.Replace("\"", "\"\"", StringComparison.Ordinal) + "\""
+            : value;
+}