fix(pooled): throw ObjectDisposedException from Count/Keys/Values after Dispose

PooledCelerityDictionary and PooledCeleritySet document that "after Dispose
every member throws ObjectDisposedException", but the read accessors Count
(both types) and Keys / Values (dictionary) skipped ThrowIfDisposed(). Since
Dispose zeroes _count and returns the backing arrays to ArrayPool.Shared, a
post-dispose read returned a silent, misleading result (0, or an empty view)
over buffers the pool may have re-handed out. Gate all three on
ThrowIfDisposed() so the code matches the documented contract, and extend the
UseAfterDispose regression tests to cover them.

Closes #296

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: marius-bughiu

CHANGELOG.md

@@ -8,6 +8,10 @@ All notable changes to Celerity are documented here. This project follows [Keep
 
 - **`Trie<TValue>`** in `Celerity.Collections` — an ordered prefix tree mapping `string` keys to values, filling a BCL gap (.NET ships no trie). `GetByPrefix` lists every entry whose key starts with a prefix in `O(prefix + matches)` and in ascending key order, and `TryGetLongestPrefix` finds the longest stored key that is a prefix of a query in `O(query)` — the autocomplete, longest-prefix-routing, and ordered-iteration workloads a `Dictionary<string, TValue>` can only answer with an `O(n)` scan plus a `StartsWith` per key. Exact `Add` / `TryGetValue` favour a `Dictionary`, so the trie earns its place on the prefix operations. Implements `IReadOnlyDictionary<string, TValue?>`; not thread-safe. Closes [#285](https://github.com/marius-bughiu/Celerity/issues/285).
 
+### Fixed
+
+- `PooledCelerityDictionary` and `PooledCeleritySet` now throw `ObjectDisposedException` from their read accessors (`Count`, and the dictionary's `Keys` / `Values`) after `Dispose`, matching the documented "every member throws after disposal" contract. Previously these returned a silent, misleading result over arrays already returned to `ArrayPool.Shared`. Closes [#296](https://github.com/marius-bughiu/Celerity/issues/296).
+
 ## [2.3.0] - 2026-07-19
 
 ### Added

src/Celerity.Tests/Collections/PooledCelerityDictionaryTests.cs

@@ -274,6 +274,15 @@ public void UseAfterDispose_ShouldThrowObjectDisposedException()
         Assert.Throws<ObjectDisposedException>(() => map.TryAdd(2, 2));
         Assert.Throws<ObjectDisposedException>(() => map.Clear());
         Assert.Throws<ObjectDisposedException>(() => map.GetEnumerator());
+        Assert.Throws<ObjectDisposedException>(() => map.EnsureCapacity(64));
+        Assert.Throws<ObjectDisposedException>(() => map.TrimExcess());
+        // Read accessors must also honour the disposed contract: Dispose returns
+        // the backing arrays to the pool, so a silent Count / Keys / Values here
+        // would report over — or enumerate — buffers the pool may have re-handed
+        // out. Regression for #296.
+        Assert.Throws<ObjectDisposedException>(() => _ = map.Count);
+        Assert.Throws<ObjectDisposedException>(() => _ = map.Keys);
+        Assert.Throws<ObjectDisposedException>(() => _ = map.Values);
     }
 
     [Fact]

src/Celerity.Tests/Collections/PooledCeleritySetTests.cs

@@ -233,6 +233,11 @@ public void UseAfterDispose_ShouldThrowObjectDisposedException()
         Assert.Throws<ObjectDisposedException>(() => set.Overlaps(new[] { 3 }));
         Assert.Throws<ObjectDisposedException>(() => set.SetEquals(new[] { 3 }));
         Assert.Throws<ObjectDisposedException>(() => set.CopyTo(new int[4], 0));
+        // Read accessor must also honour the disposed contract: Dispose zeroes
+        // _count and returns the backing array to the pool, so a silent Count
+        // here would report 0 over a buffer the pool may have re-handed out.
+        // Regression for #296.
+        Assert.Throws<ObjectDisposedException>(() => _ = set.Count);
     }
 
     [Fact]

src/Celerity/Collections/PooledCelerityDictionary.cs

@@ -202,7 +202,15 @@ private static int InitialCapacityForSource(
     /// <summary>
     /// Gets the number of key/value pairs contained in the dictionary.
     /// </summary>
-    public int Count => _count;
+    /// <exception cref="ObjectDisposedException">The dictionary has been disposed.</exception>
+    public int Count
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return _count;
+        }
+    }
 
     /// <summary>
     /// Gets or sets the value associated with the specified key.
@@ -619,13 +627,29 @@ public Enumerator GetEnumerator()
     /// Gets an enumerable view over the keys in the dictionary. The view is a
     /// lightweight struct and iterating it does not allocate.
     /// </summary>
-    public KeyCollection Keys => new KeyCollection(this);
+    /// <exception cref="ObjectDisposedException">The dictionary has been disposed.</exception>
+    public KeyCollection Keys
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return new KeyCollection(this);
+        }
+    }
 
     /// <summary>
     /// Gets an enumerable view over the values in the dictionary. The view is a
     /// lightweight struct and iterating it does not allocate.
     /// </summary>
-    public ValueCollection Values => new ValueCollection(this);
+    /// <exception cref="ObjectDisposedException">The dictionary has been disposed.</exception>
+    public ValueCollection Values
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return new ValueCollection(this);
+        }
+    }
 
     /// <summary>
     /// A struct enumerator over a

src/Celerity/Collections/PooledCeleritySet.cs

@@ -192,7 +192,15 @@ private static int InitialCapacityForSource(IEnumerable<T> source, int capacity,
     /// <summary>
     /// Gets the number of elements contained in the set.
     /// </summary>
-    public int Count => _count;
+    /// <exception cref="ObjectDisposedException">The set has been disposed.</exception>
+    public int Count
+    {
+        get
+        {
+            ThrowIfDisposed();
+            return _count;
+        }
+    }
 
     /// <summary>
     /// Adds the specified element to the set.