fix(search): cap an expression at 256 atoms

The compiled SQL chains every atom into one expression, and SQLite rejects
expressions deeper than 1000 levels. A query of about 1000 words parsed but
then failed in SQL, outside the syntax-error handling, and crashed the app.
The parser now rejects more than 256 atoms as a syntax error.

YKanBan.Tests/Search/SearchQueryParserTests.cs

@@ -248,6 +248,28 @@ public class SearchQueryParserTests
         Assert.IsNotNull(SearchQueryParser.Parse(groups));
     }
 
+    [TestMethod]
+    public void AtomCountAtTheLimitParses()
+    {
+        Assert.IsNotNull(SearchQueryParser.Parse(string.Join(" ", Enumerable.Repeat("a", SearchQueryParser.MaxAtomCount))));
+    }
+
+    [TestMethod]
+    [DataRow(" ")]
+    [DataRow(" OR ")]
+    public void AtomCountBeyondTheLimitIsAnError(string separator)
+    {
+        AssertSyntaxError(string.Join(separator, Enumerable.Repeat("a", SearchQueryParser.MaxAtomCount + 1)));
+    }
+
+    [TestMethod]
+    public void QualifiersAndPhrasesCountTowardsTheAtomLimit()
+    {
+        int half = SearchQueryParser.MaxAtomCount / 2;
+        string text = string.Join(" ", Enumerable.Repeat("tag:\"a b\"", half).Concat(Enumerable.Repeat("\"c\"", half + 1)));
+        AssertSyntaxError(text);
+    }
+
     [TestMethod]
     public void VeryDeepNestingIsAnErrorRatherThanACrash()
     {