test(core/browser/platform): 26 extreme RED/GREEN TDD cycles and full regression hardening (3,235 PASS)

tests/Paca.Tests/Core/SecurityAndConfigExtremeRedTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Paca.Core.Config;
+using Paca.Core.Security;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+public class SecurityAndConfigExtremeRedTests
+{
+    private const string TestBase32Secret = "JBSWY3DPEHPK3PXP"; // "Hello!" in Base32
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(-10)]
+    [InlineData(-1)]
+    public void TotpEngine_ZeroOrNegativeTimeStep_DoesNotThrowDivideByZero(int timeStep)
+    {
+        var ex = Record.Exception(() =>
+            TotpEngine.GenerateCurrentCode(TestBase32Secret, timeStepSeconds: timeStep));
+        Assert.Null(ex);
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(-30)]
+    public void TotpEngine_GetRemainingSeconds_ZeroOrNegativeTimeStep_DoesNotThrowDivideByZero(int timeStep)
+    {
+        var ex = Record.Exception(() =>
+            TotpEngine.GetRemainingSeconds(timeStepSeconds: timeStep));
+        Assert.Null(ex);
+        var remaining = TotpEngine.GetRemainingSeconds(timeStepSeconds: timeStep);
+        Assert.True(remaining > 0);
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(-5)]
+    [InlineData(20)]
+    public void TotpEngine_InvalidDigits_ClampedToValidRange(int digits)
+    {
+        var code = TotpEngine.GenerateCurrentCode(TestBase32Secret, digits: digits);
+        Assert.True(code.Length >= 6 && code.Length <= 8);
+    }
+
+    [Fact]
+    public void CredentialSecurityAuditor_NullCredentials_ReturnsSafeReport()
+    {
+        var report = CredentialSecurityAuditor.PerformAudit(null!);
+        Assert.NotNull(report);
+        Assert.Equal(0, report.TotalAccounts);
+        Assert.Equal(100, report.OverallHealthScore);
+    }
+
+    [Fact]
+    public void CredentialSecurityAuditor_NegativeDays_ClampsToPositive()
+    {
+        var cred = new SiteCredentialRecord
+        {
+            Id = "1",
+            Domain = "example.com",
+            Username = "user",
+            DecryptedPassword = "SuperSecurePassword123!",
+            CreatedAt = DateTime.UtcNow,
+            LastModifiedAt = DateTime.UtcNow
+        };
+
+        var report = CredentialSecurityAuditor.PerformAudit(new[] { cred }, oldPasswordDays: -10);
+        Assert.Equal(0, report.OldPasswordCount);
+    }
+
+    [Fact]
+    public void CredentialSecurityAuditor_RecentlyModified_NotMarkedAsOldEvenIfCreatedLongAgo()
+    {
+        var cred = new SiteCredentialRecord
+        {
+            Id = "1",
+            Domain = "example.com",
+            Username = "user",
+            DecryptedPassword = "SuperSecurePassword123!",
+            CreatedAt = DateTime.UtcNow.AddDays(-200), // Created 200 days ago
+            LastModifiedAt = DateTime.UtcNow // But modified today!
+        };
+
+        var report = CredentialSecurityAuditor.PerformAudit(new[] { cred }, oldPasswordDays: 90);
+        Assert.Equal(0, report.OldPasswordCount);
+        Assert.DoesNotContain(report.Issues, i => i.IssueType == "OldPassword");
+    }
+
+    [Fact]
+    public void WorkspaceConfigSanitizer_ExcessiveWorkspaces_CappedTo20()
+    {
+        var many = Enumerable.Range(1, 100).Select(i => $"Workspace_{i}").ToList();
+        var sanitized = WorkspaceConfigSanitizer.Sanitize(many);
+        Assert.True(sanitized.Count <= 20);
+    }
+
+    [Fact]
+    public void WorkspaceConfigSanitizer_OverlyLongName_TruncatedSafely()
+    {
+        var longName = new string('A', 200);
+        var sanitized = WorkspaceConfigSanitizer.Sanitize(new[] { longName });
+        Assert.Single(sanitized);
+        Assert.True(sanitized[0].Length <= 30);
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void PasswordSecurityEngine_EvaluateStrength_NullOrWhitespace_ReturnsZeroScore(string? emptyPass)
+    {
+        var result = PasswordSecurityEngine.EvaluateStrength(emptyPass!);
+        Assert.NotNull(result);
+        Assert.Equal(0, result.Score);
+        Assert.Equal(PasswordGrade.VeryWeak, result.Grade);
+    }
+}