Make agent file writes append by default

MeetingAssistant.Tests/WorkflowRulesEditorTests.cs

@@ -82,6 +82,46 @@ public sealed class WorkflowRulesEditorTests
         Assert.DoesNotContain("other.yaml", searchResult);
     }
 
+    [Fact]
+    public async Task RulesEditorToolsAppendByDefaultAndReplaceOnlyWhenRequested()
+    {
+        var root = Path.Combine(Path.GetTempPath(), "meeting-assistant-tests", Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(root);
+        var rulesPath = Path.Combine(root, "rules.yaml");
+        await File.WriteAllTextAsync(
+            rulesPath,
+            """
+            rules:
+            - name: existing
+              on:
+                - created: {}
+              steps:
+                - uses: add_attendee
+                  value: Ada
+            """);
+        var tools = new WorkflowRulesEditorTools(new MeetingAssistantOptions
+        {
+            Automation = new AutomationOptions { RulesPath = rulesPath }
+        });
+
+        await tools.WriteRules("""
+            - name: appended
+              on:
+                - created: {}
+              steps:
+                - uses: add_attendee
+                  value: Grace
+            """);
+
+        var appended = await File.ReadAllTextAsync(rulesPath);
+        Assert.Contains("name: existing", appended);
+        Assert.Contains("name: appended", appended);
+
+        await tools.WriteRules("rules: []", replace_file: true);
+
+        Assert.Equal("rules: []", await File.ReadAllTextAsync(rulesPath));
+    }
+
     [Fact]
     public async Task RulesEditorToolsRefuseInvalidYamlWithoutOverwritingFile()
     {
@@ -94,7 +134,7 @@ public sealed class WorkflowRulesEditorTests
             Automation = new AutomationOptions { RulesPath = rulesPath }
         });
 
-        var result = await tools.WriteRules("rules:\n- name: [");
+        var result = await tools.WriteRules("rules:\n- name: [", replace_file: true);
 
         Assert.StartsWith("Refused: workflow rules YAML is invalid.", result);
         Assert.Equal("rules: []", await File.ReadAllTextAsync(rulesPath));