feat(mode): Preserve set tags and include tags in PreserveUnknownExecutionMode

Enable deferredExecutionMode to preserve set tags in output while still
evaluating their right-hand side expressions. This allows multi-pass
rendering where:
- `{% set a = 1 %}` is preserved as-is
- `{% set b = a %}` becomes `{% set b = 1 %}` (RHS evaluated)
- Unknown variables remain deferred: `{% set x = unknown %}`

Also added tests for include tag behavior with unknown paths and
unknown variables in included templates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: hs-lsong

src/main/java/com/hubspot/jinjava/mode/PreserveUnknownExecutionMode.java

@@ -42,5 +42,6 @@ public void prepareContext(Context context) {
       .forEach(maybeEagerTag -> context.registerTag(maybeEagerTag.get()));
 
     context.setDynamicVariableResolver(varName -> DeferredValue.instance());
+    context.setDeferredExecutionMode(true);
   }
 }

src/test/java/com/hubspot/jinjava/mode/PreserveUnknownExecutionModeTest.java

@@ -4,6 +4,9 @@
 
 import com.hubspot.jinjava.Jinjava;
 import com.hubspot.jinjava.JinjavaConfig;
+import com.hubspot.jinjava.loader.ResourceLocator;
+import java.io.IOException;
+import java.nio.charset.Charset;
 import java.util.HashMap;
 import java.util.Map;
 import org.junit.Before;
@@ -115,4 +118,79 @@ public void itPreservesComplexExpression() {
     String result = jinjava.render(template, new HashMap<>());
     assertThat(result).isEqualTo("{{ obj.property }}");
   }
+
+  @Test
+  public void itPreservesIncludeWithUnknownPath() {
+    String template = "{% include unknown_path %}";
+    String result = jinjava.render(template, new HashMap<>());
+    assertThat(result).isEqualTo("{% include unknown_path %}");
+  }
+
+  @Test
+  public void itRendersIncludeWithKnownPath() {
+    jinjava.setResourceLocator(
+      new ResourceLocator() {
+        @Override
+        public String getString(
+          String fullName,
+          Charset encoding,
+          com.hubspot.jinjava.interpret.JinjavaInterpreter interpreter
+        ) throws IOException {
+          if ("test.html".equals(fullName)) {
+            return "included content";
+          }
+          throw new IOException("Template not found: " + fullName);
+        }
+      }
+    );
+    String template = "{% include 'test.html' %}";
+    String result = jinjava.render(template, new HashMap<>());
+    assertThat(result).isEqualTo("included content");
+  }
+
+  @Test
+  public void itPreservesUnknownVariablesInIncludedTemplate() {
+    jinjava.setResourceLocator(
+      new ResourceLocator() {
+        @Override
+        public String getString(
+          String fullName,
+          Charset encoding,
+          com.hubspot.jinjava.interpret.JinjavaInterpreter interpreter
+        ) throws IOException {
+          if ("test.html".equals(fullName)) {
+            return "Hello {{ unknown_var }}";
+          }
+          throw new IOException("Template not found: " + fullName);
+        }
+      }
+    );
+    String template = "{% include 'test.html' %}";
+    String result = jinjava.render(template, new HashMap<>());
+    assertThat(result).isEqualTo("Hello {{ unknown_var }}");
+  }
+
+  @Test
+  public void itPreservesSetWithUnknownValue() {
+    String template = "{% set var = unknown %}{{ var }}";
+    String result = jinjava.render(template, new HashMap<>());
+    assertThat(result).isEqualTo("{% set var = unknown %}{{ var }}");
+  }
+
+  @Test
+  public void itPreservesSetWithLiteralValue() {
+    String template = "{% set a = 1 %}{{ a }}";
+    String result = jinjava.render(template, new HashMap<>());
+    // With deferredExecutionMode=true, set tag is preserved but {{ a }} is evaluated to 1
+    assertThat(result).isEqualTo("{% set a = 1 %}1");
+  }
+
+  @Test
+  public void itEvaluatesSetRightSideWhenPossible() {
+    String template = "{% set a = 1 %}{% set b = a %}{{ b }}";
+    String result = jinjava.render(template, new HashMap<>());
+    // Both set tags are preserved with evaluated right-hand sides
+    // {{ b }} is evaluated because b is known (set to 1)
+    assertThat(result).isEqualTo("{% set a = 1 %}{% set b = 1 %}1");
+  }
 }