@@ -0,0 +1,122 @@
+//
+// Copyright (c) 2019-2026 Angouri.
+// AngouriMath is licensed under MIT.
+// Details: https://github.com/asc-community/AngouriMath/blob/master/LICENSE.md.
+// Website: https://am.angouri.org.
+//
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Threading.Tasks;
+using AngouriMath;
+using AngouriMath.Extensions;
+using Xunit;
+
+namespace AngouriMath.Tests.Common
+{
+    /// <summary>
+    /// Every node survives every pipeline: no crash, no hang, no exception the caller has no
+    /// reason to expect.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// The generalisation of <c>LimitTerminatesOnEveryNodeTest</c>. Limits were where the
+    /// hole showed — seven node types killed the process by inheriting a default that
+    /// returned the node instead of <see langword="null"/> — but nothing made limits special.
+    /// A node reaches a dozen pipelines and <c>Docs/Contributing/AddingNode.cs</c> lists
+    /// them; anything missed there is missed silently, because the node that breaks is
+    /// exactly the one nobody wrote a test for.
+    /// </para>
+    /// <para>
+    /// So the node types are enumerated rather than listed, and each is put through every
+    /// pipeline. What is asserted is only what every pipeline owes a caller: return, in
+    /// finite time, either an answer or an <see cref="AngouriMath.Core.Exceptions.AngouriMathBaseException"/>.
+    /// Not that the answer is right — the per-node tests are for that — and not that there
+    /// is one at all, since an unevaluated node is a legitimate answer here.
+    /// </para>
+    /// https://github.com/asc-community/AngouriMath/issues/829
+    /// </remarks>
+    [Trait("Area", "Common")]
+    public sealed class EveryNodeSurvivesEveryPipelineTest
+    {
+        private static readonly Entity.Variable X = MathS.Var("x");
+
+        public static IEnumerable<object[]> EveryNodeType()
+        {
+            var built = new List<Entity>();
+            foreach (var type in typeof(Entity).Assembly.GetTypes()
+                         .Where(t => t.IsSealed && !t.IsAbstract && typeof(Entity).IsAssignableFrom(t))
+                         .OrderBy(t => t.FullName, StringComparer.Ordinal))
+            {
+                var constructor = type.GetConstructors(BindingFlags.Public | BindingFlags.Instance)
+                    .Where(c => c.GetParameters().Length > 0
+                                && c.GetParameters().All(p => p.ParameterType == typeof(Entity)))
+                    .OrderBy(c => c.GetParameters().Length)
+                    .FirstOrDefault();
+                if (constructor is null)
+                    continue;
+                try
+                {
+                    built.Add((Entity)constructor.Invoke(
+                        constructor.GetParameters().Select(_ => (object)(Entity)X).ToArray()));
+                }
+                catch (Exception) { /* a node that will not take a bare variable is not the subject */ }
+            }
+            Assert.NotEmpty(built);
+            return built.Select(n => new object[] { n });
+        }
+
+        /// <summary>
+        /// The pipelines a node reaches, named so a failure says which one broke.
+        /// </summary>
+        private static readonly (string Name, Action<Entity> Run)[] Pipelines =
+        {
+            ("Stringize",     e => e.Stringize()),
+            ("Latexise",      e => e.Latexise()),
+            ("ToString",      e => e.ToString()),
+            ("InnerSimplified", e => { _ = e.InnerSimplified; }),
+            ("Evaled",        e => { _ = e.Evaled; }),
+            ("Simplify",      e => e.Simplify()),
+            ("Expand",        e => e.Expand()),
+            ("Factorize",     e => e.Factorize()),
+            ("Differentiate", e => e.Differentiate(X)),
+            ("Integrate",     e => e.Integrate(X)),
+            ("Substitute",    e => e.Substitute(X, 2)),
+            ("Vars",          e => { _ = e.Vars.Count; }),
+            ("Nodes",         e => { _ = e.Nodes.Count(); }),
+            ("Complexity",    e => { _ = e.Complexity; }),
+            ("Solve",         e => e.SolveEquation(X)),
+        };
+
+        [Theory]
+        [MemberData(nameof(EveryNodeType))]
+        public void EveryPipelineReturns(Entity node)
+        {
+            var broken = new List<string>();
+            foreach (var (name, run) in Pipelines)
+            {
+                // Each in a task with a timeout: a regression here is non-termination, and
+                // the suite must fail rather than hang. A stack overflow cannot be caught at
+                // all, so the signal for that one is the run aborting.
+                string? failure = null;
+                var finished = Task.Run(() =>
+                {
+                    try { run(node); }
+                    catch (AngouriMath.Core.Exceptions.AngouriMathBaseException) { /* the library's own, and legitimate */ }
+                    catch (NotSupportedException) { /* documented refusal, e.g. uncompilable shapes */ }
+                    catch (Exception e) { failure = e.GetType().FullName + ": " + e.Message.Split('\n')[0]; }
+                }).Wait(TimeSpan.FromSeconds(30));
+
+                if (!finished)
+                    broken.Add($"{name} did not terminate");
+                else if (failure is { })
+                    broken.Add($"{name} threw {failure}");
+            }
+
+            Assert.True(broken.Count is 0,
+                $"{node.Stringize()} [{node.GetType().Name}]:\n  " + string.Join("\n  ", broken));
+        }
+    }
+}