fix: return error for reserved property keys in UpdateProperties::Set() (#817)

Previously, reserved table properties (except `format-version`) were
silently ignored when set via `UpdateProperties::Set()`. This caused
undetected configuration drift compared to Java, which throws exceptions
for such attempts.

Now attempts to set reserved properties accumulate a validation error
via `ICEBERGER_BUILDER_CHECK`, surfaced at `Apply()` time. This matches
Java's loud-failure behavior.

Author: WZhuo

src/iceberg/test/update_properties_test.cc

@@ -129,6 +129,53 @@ TEST_F(UpdatePropertiesTest, UpgradeFormatVersionUnsupported) {
   EXPECT_THAT(result, HasErrorMessage("unsupported format version"));
 }
 
+TEST_F(UpdatePropertiesTest, SetReservedPropertyUuid) {
+  ICEBERG_UNWRAP_OR_FAIL(auto update, table_->NewUpdateProperties());
+  update->Set("uuid", "some-uuid");
+
+  auto result = update->Apply();
+  EXPECT_THAT(result, IsError(ErrorKind::kValidationFailed));
+  EXPECT_THAT(result, HasErrorMessage("Cannot set reserved property"));
+}
+
+TEST_F(UpdatePropertiesTest, SetReservedPropertyCurrentSchema) {
+  ICEBERG_UNWRAP_OR_FAIL(auto update, table_->NewUpdateProperties());
+  update->Set("current-schema", R"({"type": "struct"})");
+
+  auto result = update->Apply();
+  EXPECT_THAT(result, IsError(ErrorKind::kValidationFailed));
+  EXPECT_THAT(result, HasErrorMessage("Cannot set reserved property"));
+}
+
+TEST_F(UpdatePropertiesTest, SetReservedPropertyCurrentSnapshotId) {
+  ICEBERG_UNWRAP_OR_FAIL(auto update, table_->NewUpdateProperties());
+  update->Set("current-snapshot-id", "12345");
+
+  auto result = update->Apply();
+  EXPECT_THAT(result, IsError(ErrorKind::kValidationFailed));
+  EXPECT_THAT(result, HasErrorMessage("Cannot set reserved property"));
+}
+
+TEST_F(UpdatePropertiesTest, SetFormatVersionStillAllowed) {
+  ICEBERG_UNWRAP_OR_FAIL(auto update, table_->NewUpdateProperties());
+  update->Set("format-version", "3");
+
+  ICEBERG_UNWRAP_OR_FAIL(auto result, update->Apply());
+  EXPECT_TRUE(result.updates.empty());
+  ASSERT_TRUE(result.format_version.has_value());
+  EXPECT_EQ(result.format_version.value(), 3);
+}
+
+TEST_F(UpdatePropertiesTest, SetValidAndReservedProperties) {
+  ICEBERG_UNWRAP_OR_FAIL(auto update, table_->NewUpdateProperties());
+  update->Set("valid.key", "valid.value");
+  update->Set("snapshot-count", "10");
+
+  auto result = update->Apply();
+  EXPECT_THAT(result, IsError(ErrorKind::kValidationFailed));
+  EXPECT_THAT(result, HasErrorMessage("Cannot set reserved property"));
+}
+
 TEST_F(UpdatePropertiesTest, CommitSuccess) {
   ICEBERG_UNWRAP_OR_FAIL(auto empty_update, table_->NewUpdateProperties());
   EXPECT_THAT(empty_update->Commit(), IsOk());

src/iceberg/update/update_properties.cc

@@ -50,10 +50,10 @@ UpdateProperties& UpdateProperties::Set(const std::string& key,
                         "Cannot set property '{}' that is already marked for removal",
                         key);
 
-  if (!TableProperties::reserved_properties().contains(key) ||
-      key == TableProperties::kFormatVersion.key()) {
-    updates_.insert_or_assign(key, value);
-  }
+  ICEBERG_BUILDER_CHECK(!TableProperties::reserved_properties().contains(key) ||
+                            key == TableProperties::kFormatVersion.key(),
+                        "Cannot set reserved property: '{}'", key);
+  updates_.insert_or_assign(key, value);
 
   return *this;
 }

src/iceberg/update/update_properties.h

@@ -51,8 +51,9 @@ class ICEBERG_EXPORT UpdateProperties : public PendingUpdate {
 
   /// \brief Sets a property key to a specified value.
   ///
-  /// The key must not have been previously marked for removal and reserved property keys
-  /// will be ignored.
+  /// The key must not have been previously marked for removal and must not be a
+  /// reserved property key (except `format-version`). Setting a reserved property
+  /// will result in a validation error at Apply() time.
   ///
   /// \param key The property key to set
   /// \param value The property value to set