Handle default timestamps consistently

Author: adwsingh

mcp/mcp-server/src/it/java/software/amazon/smithy/java/mcp/server/McpServerIntegrationTest.java

@@ -275,6 +275,8 @@ void testEchoSchemaTypeMapping() throws Exception {
             assertEquals("number", echoProps.path("epochSecondsTimestamp").path("type").asText());
             assertEquals("string", echoProps.path("dateTimeTimestamp").path("type").asText());
             assertEquals("string", echoProps.path("httpDateTimestamp").path("type").asText());
+            // Default timestamp (no format trait) should be string (date-time format)
+            assertEquals("string", echoProps.path("defaultTimestamp").path("type").asText());
 
             // Enum should be string with enum values
             assertEquals("string", echoProps.path("enumValue").path("type").asText());
@@ -435,6 +437,15 @@ void testHttpDateTimestampRoundTrip() {
         assertEquals(httpDateStr, echo.getMember("httpDateTimestamp").asString());
     }
 
+    @Test
+    void testDefaultTimestampRoundTrip() {
+        initializeLatestProtocol();
+        // Default format is date-time (ISO 8601 string)
+        var dateTimeStr = "2023-11-14T22:13:20Z";
+        var echo = echoSingleField("defaultTimestamp", Document.of(dateTimeStr));
+        assertEquals(dateTimeStr, echo.getMember("defaultTimestamp").asString());
+    }
+
     // ========== List Tests ==========
 
     @Test
@@ -796,6 +807,7 @@ void testInputFieldsAreCorrectlyDeserialized() {
         echoData.put("epochSecondsTimestamp", Document.of(1700000000.0));
         echoData.put("dateTimeTimestamp", Document.of("2023-11-14T22:13:20Z"));
         echoData.put("httpDateTimestamp", Document.of("Tue, 14 Nov 2023 22:13:20 GMT"));
+        echoData.put("defaultTimestamp", Document.of("2023-11-14T22:13:20Z"));
         echoData.put("stringList", Document.of(List.of(Document.of("a"), Document.of("b"))));
         echoData.put("integerList", Document.of(List.of(Document.of(1), Document.of(2))));
         echoData.put("stringMap", Document.of(Map.of("key1", Document.of("value1"))));
@@ -833,6 +845,7 @@ void testInputFieldsAreCorrectlyDeserialized() {
         assertNotNull(echo.getEpochSecondsTimestamp());
         assertNotNull(echo.getDateTimeTimestamp());
         assertNotNull(echo.getHttpDateTimestamp());
+        assertNotNull(echo.getDefaultTimestamp());
 
         // Verify collections
         assertEquals(2, echo.getStringList().size());
@@ -941,6 +954,7 @@ void testAllTypesValidateAgainstOutputSchema() throws Exception {
         echoData.put("epochSecondsTimestamp", Document.of(1700000000.0));
         echoData.put("dateTimeTimestamp", Document.of("2023-11-14T22:13:20Z"));
         echoData.put("httpDateTimestamp", Document.of("Tue, 14 Nov 2023 22:13:20 GMT"));
+        echoData.put("defaultTimestamp", Document.of("2023-11-14T22:13:20Z"));
         echoData.put("stringList", Document.of(List.of(Document.of("a"))));
         echoData.put("integerList", Document.of(List.of(Document.of(1))));
         echoData.put("nestedList", Document.of(List.of(nested)));

mcp/mcp-server/src/it/resources/META-INF/smithy/main.smithy

@@ -96,6 +96,8 @@ structure Echo {
     dateTimeTimestamp: Timestamp
     @timestampFormat("http-date")
     httpDateTimestamp: Timestamp
+    // Default timestamp (no format trait - defaults to date-time)
+    defaultTimestamp: Timestamp
 
     // Collections
     stringList: StringList

mcp/mcp-server/src/main/java/software/amazon/smithy/java/mcp/server/McpService.java

@@ -690,15 +690,11 @@ private static String memberDescription(Schema schema) {
     }
 
     private static JsonPrimitiveType resolveTimestampType(Schema schema) {
-        var trait = schema.getTrait(TraitKey.TIMESTAMP_FORMAT_TRAIT);
-        if (trait == null) {
-            // default is epoch-seconds
-            return JsonPrimitiveType.NUMBER;
-        }
-        return switch (trait.getFormat()) {
+        var format = getFormat(schema.getTrait(TraitKey.TIMESTAMP_FORMAT_TRAIT));
+        return switch (format) {
             case EPOCH_SECONDS -> JsonPrimitiveType.NUMBER;
             case DATE_TIME, HTTP_DATE -> JsonPrimitiveType.STRING;
-            case UNKNOWN -> throw new RuntimeException("unknown timestamp format: " + trait.getFormat());
+            case UNKNOWN -> throw new RuntimeException("unknown timestamp format: " + format);
         };
     }