diff --git a/src/engine/BUILD.bazel b/src/engine/BUILD.bazel
index 3ac7ec7d8..1ee3f105a 100644
--- a/src/engine/BUILD.bazel
+++ b/src/engine/BUILD.bazel
@@ -41,6 +41,9 @@ mozc_cc_library(
     name = "data_loader",
     srcs = ["data_loader.cc"],
     hdrs = ["data_loader.h"],
+    visibility = [
+        "//engine:__subpackages__",
+    ],
     deps = [
         ":modules",
         "//base:file_util",
@@ -360,6 +363,9 @@ mozc_cc_library(
     name = "minimal_converter",
     srcs = ["minimal_converter.cc"],
     hdrs = ["minimal_converter.h"],
+    visibility = [
+        "//engine:__subpackages__",
+    ],
     deps = [
         ":engine_converter",
         ":engine_converter_interface",
@@ -479,7 +485,6 @@ mozc_cc_library(
     hdrs = ["candidate_list.h"],
     visibility = [
         "//engine:__subpackages__",
-        "//session:__subpackages__",
     ],
     deps = [
         "//base:hash",
@@ -496,7 +501,6 @@ mozc_cc_library(
     hdrs = ["engine_output.h"],
     visibility = [
         "//engine:__subpackages__",
-        "//session:__subpackages__",
     ],
     deps = [
         ":candidate_list",
diff --git a/src/engine/engine_converter.cc b/src/engine/engine_converter.cc
index ab12338e5..e2a76bb73 100644
--- a/src/engine/engine_converter.cc
+++ b/src/engine/engine_converter.cc
@@ -792,7 +792,7 @@ void EngineConverter::CommitPreedit(const composer::Composer &composer,
   const std::string key = composer.GetQueryForConversion();
   const std::string preedit = composer.GetStringForSubmission();
   std::string normalized_preedit = TextNormalizer::NormalizeText(preedit);
-  EngineOutput::FillPreeditResult(preedit, &result_);
+  output::FillPreeditResult(preedit, &result_);
 
   // Add ResultToken
   commands::ResultToken *token = result_.add_tokens();
@@ -800,8 +800,8 @@ void EngineConverter::CommitPreedit(const composer::Composer &composer,
   token->set_value(preedit);
 
   // Cursor offset needs to be calculated based on normalized text.
-  EngineOutput::FillCursorOffsetResult(
-      CalculateCursorOffset(normalized_preedit), &result_);
+  output::FillCursorOffsetResult(CalculateCursorOffset(normalized_preedit),
+                                 &result_);
   segments_.InitForCommit(key, normalized_preedit);
   CommitUsageStats(EngineConverterInterface::COMPOSITION, context);
   DCHECK(request_);
@@ -828,9 +828,8 @@ void EngineConverter::CommitHead(size_t count,
   }
   Util::Utf8SubString(preedit, 0, *consumed_key_size, &preedit);
   const std::string composition = TextNormalizer::NormalizeText(preedit);
-  EngineOutput::FillPreeditResult(composition, &result_);
-  EngineOutput::FillCursorOffsetResult(CalculateCursorOffset(composition),
-                                       &result_);
+  output::FillPreeditResult(composition, &result_);
+  output::FillCursorOffsetResult(CalculateCursorOffset(composition), &result_);
 }
 
 void EngineConverter::Revert() { converter_->RevertConversion(&segments_); }
@@ -1080,6 +1079,11 @@ void MaybeFillConfig(Segment::Candidate::Command command,
 }
 }  // namespace
 
+void EngineConverter::FillPreedit(const composer::Composer &composer,
+                                  commands::Preedit *preedit) const {
+  output::FillPreedit(composer, preedit);
+}
+
 void EngineConverter::FillOutput(const composer::Composer &composer,
                                  commands::Output *output) const {
   if (!output) {
@@ -1091,7 +1095,7 @@ void EngineConverter::FillOutput(const composer::Composer &composer,
   }
   if (CheckState(COMPOSITION)) {
     if (!composer.Empty()) {
-      EngineOutput::FillPreedit(composer, output->mutable_preedit());
+      output::FillPreedit(composer, output->mutable_preedit());
     }
   }
 
@@ -1106,7 +1110,7 @@ void EngineConverter::FillOutput(const composer::Composer &composer,
     // When the suggestion comes from zero query suggestion, the
     // composer is empty.  In that case, preedit is not rendered.
     if (!composer.Empty()) {
-      EngineOutput::FillPreedit(composer, output->mutable_preedit());
+      output::FillPreedit(composer, output->mutable_preedit());
     }
   } else if (CheckState(PREDICTION | CONVERSION)) {
     // Conversion on Prediction or Conversion
@@ -1128,7 +1132,7 @@ void EngineConverter::FillOutput(const composer::Composer &composer,
 
   // For debug. Removed candidate words through the conversion process.
   if (CheckState(SUGGESTION | PREDICTION | CONVERSION)) {
-    EngineOutput::FillRemovedCandidates(
+    output::FillRemovedCandidates(
         segments_.conversion_segment(segment_index_),
         output->mutable_removed_candidate_words_for_debug());
   }
@@ -1349,9 +1353,8 @@ bool EngineConverter::UpdateResult(size_t index, size_t size,
   if (consumed_key_size) {
     *consumed_key_size = GetConsumedPreeditSize(index, size);
   }
-  EngineOutput::FillConversionResult(preedit, conversion, &result_);
-  EngineOutput::FillCursorOffsetResult(CalculateCursorOffset(conversion),
-                                       &result_);
+  output::FillConversionResult(preedit, conversion, &result_);
+  output::FillCursorOffsetResult(CalculateCursorOffset(conversion), &result_);
   UpdateResultTokens(index, size);
   return true;
 }
@@ -1480,8 +1483,8 @@ const Segment::Candidate &EngineConverter::GetSelectedCandidate(
 
 void EngineConverter::FillConversion(commands::Preedit *preedit) const {
   DCHECK(CheckState(PREDICTION | CONVERSION));
-  EngineOutput::FillConversion(segments_, segment_index_,
-                               candidate_list_.focused_id(), preedit);
+  output::FillConversion(segments_, segment_index_,
+                         candidate_list_.focused_id(), preedit);
 }
 
 void EngineConverter::FillResult(commands::Result *result) const {
@@ -1514,13 +1517,13 @@ void EngineConverter::FillCandidateWindow(
   }
 
   const Segment &segment = segments_.conversion_segment(segment_index_);
-  EngineOutput::FillCandidateWindow(segment, candidate_list_, position,
-                                    candidate_window);
+  output::FillCandidateWindow(segment, candidate_list_, position,
+                              candidate_window);
 
   // Shortcut keys
   if (CheckState(PREDICTION | CONVERSION)) {
-    EngineOutput::FillShortcuts(GetCandidateShortcuts(selection_shortcut_),
-                                candidate_window);
+    output::FillShortcuts(GetCandidateShortcuts(selection_shortcut_),
+                          candidate_window);
   }
 
   // Store category
@@ -1570,7 +1573,7 @@ void EngineConverter::FillCandidateWindow(
   }
 
   // Store footer.
-  EngineOutput::FillFooter(candidate_window->category(), candidate_window);
+  output::FillFooter(candidate_window->category(), candidate_window);
 }
 
 void EngineConverter::FillAllCandidateWords(
@@ -1606,8 +1609,7 @@ void EngineConverter::FillAllCandidateWords(
     return;
   }
   const Segment &segment = segments_.conversion_segment(segment_index_);
-  EngineOutput::FillAllCandidateWords(segment, candidate_list_, category,
-                                      candidates);
+  output::FillAllCandidateWords(segment, candidate_list_, category, candidates);
 }
 
 void EngineConverter::FillIncognitoCandidateWords(
diff --git a/src/engine/engine_converter.h b/src/engine/engine_converter.h
index 886edbb94..435137d0d 100644
--- a/src/engine/engine_converter.h
+++ b/src/engine/engine_converter.h
@@ -226,6 +226,10 @@ class EngineConverter : public EngineConverterInterface {
   void PopOutput(const composer::Composer &composer,
                  commands::Output *output) override;
 
+  // Fills preedit
+  void FillPreedit(const composer::Composer &composer,
+                   commands::Preedit *preedit) const override;
+
   // Fills protocol buffers
   void FillOutput(const composer::Composer &composer,
                   commands::Output *output) const override;
diff --git a/src/engine/engine_converter_interface.h b/src/engine/engine_converter_interface.h
index 794536fc5..307b2095e 100644
--- a/src/engine/engine_converter_interface.h
+++ b/src/engine/engine_converter_interface.h
@@ -213,6 +213,10 @@ class EngineConverterInterface {
   virtual void PopOutput(const composer::Composer &composer,
                          commands::Output *output) = 0;
 
+  // Fill preedit
+  virtual void FillPreedit(const composer::Composer &composer,
+                           commands::Preedit *preedit) const = 0;
+
   // Fill protocol buffers
   virtual void FillOutput(const composer::Composer &composer,
                           commands::Output *output) const = 0;
diff --git a/src/engine/engine_output.cc b/src/engine/engine_output.cc
index a0e0bf148..54ab13662 100644
--- a/src/engine/engine_output.cc
+++ b/src/engine/engine_output.cc
@@ -161,13 +161,12 @@ void FillAllCandidateWordsInternal(
                       candidate_word_proto);
   }
 }
-
 }  // namespace
 
-// static
-void EngineOutput::FillCandidate(
-    const Segment &segment, const Candidate &candidate,
-    commands::CandidateWindow_Candidate *candidate_proto) {
+namespace output {
+
+void FillCandidate(const Segment &segment, const Candidate &candidate,
+                   commands::CandidateWindow_Candidate *candidate_proto) {
   DCHECK(segment.is_valid_index(candidate.id()));
 
   if (candidate.HasSubcandidateList()) {
@@ -191,10 +190,10 @@ void EngineOutput::FillCandidate(
   }
 }
 
-// static
-void EngineOutput::FillCandidateWindow(
-    const Segment &segment, const CandidateList &candidate_list,
-    const size_t position, commands::CandidateWindow *candidate_window_proto) {
+void FillCandidateWindow(const Segment &segment,
+                         const CandidateList &candidate_list,
+                         const size_t position,
+                         commands::CandidateWindow *candidate_window_proto) {
   if (candidate_list.focused()) {
     candidate_window_proto->set_focused_index(candidate_list.focused_index());
   }
@@ -233,20 +232,18 @@ void EngineOutput::FillCandidateWindow(
   FillUsages(segment, candidate_list, candidate_window_proto);
 }
 
-// static
-void EngineOutput::FillAllCandidateWords(
-    const Segment &segment, const CandidateList &candidate_list,
-    const commands::Category category,
-    commands::CandidateList *candidate_list_proto) {
+void FillAllCandidateWords(const Segment &segment,
+                           const CandidateList &candidate_list,
+                           const commands::Category category,
+                           commands::CandidateList *candidate_list_proto) {
   candidate_list_proto->set_category(category);
   FillAllCandidateWordsInternal(segment, candidate_list,
                                 candidate_list.focused_id(),
                                 candidate_list_proto);
 }
 
-// static
-void EngineOutput::FillRemovedCandidates(
-    const Segment &segment, commands::CandidateList *candidate_list_proto) {
+void FillRemovedCandidates(const Segment &segment,
+                           commands::CandidateList *candidate_list_proto) {
   int index = 1000;
   absl::Span<const Segment::Candidate> candidates =
       segment.removed_candidates_for_debug_;
@@ -258,9 +255,7 @@ void EngineOutput::FillRemovedCandidates(
   }
 }
 
-// static
-bool EngineOutput::ShouldShowUsages(const Segment &segment,
-                                    const CandidateList &cand_list) {
+bool ShouldShowUsages(const Segment &segment, const CandidateList &cand_list) {
   // Check if the shown candidate have the usage data.
   for (const Candidate &candidate_ptr : cand_list.focused_page()) {
     if (candidate_ptr.HasSubcandidateList()) {
@@ -273,10 +268,8 @@ bool EngineOutput::ShouldShowUsages(const Segment &segment,
   return false;
 }
 
-// static
-void EngineOutput::FillUsages(
-    const Segment &segment, const CandidateList &cand_list,
-    commands::CandidateWindow *candidate_window_proto) {
+void FillUsages(const Segment &segment, const CandidateList &cand_list,
+                commands::CandidateWindow *candidate_window_proto) {
   if (!ShouldShowUsages(segment, cand_list)) {
     return;
   }
@@ -319,10 +312,8 @@ void EngineOutput::FillUsages(
   }
 }
 
-// static
-void EngineOutput::FillShortcuts(
-    absl::string_view shortcuts,
-    commands::CandidateWindow *candidate_window_proto) {
+void FillShortcuts(absl::string_view shortcuts,
+                   commands::CandidateWindow *candidate_window_proto) {
   const size_t num_loop = std::min<size_t>(
       candidate_window_proto->candidate_size(), shortcuts.size());
   for (size_t i = 0; i < num_loop; ++i) {
@@ -332,8 +323,7 @@ void EngineOutput::FillShortcuts(
   }
 }
 
-// static
-void EngineOutput::FillSubLabel(commands::Footer *footer) {
+void FillSubLabel(commands::Footer *footer) {
   // Delete the label because sub_label will be drawn on the same
   // place for the label.
   footer->clear_label();
@@ -351,9 +341,8 @@ void EngineOutput::FillSubLabel(commands::Footer *footer) {
   }
 }
 
-// static
-bool EngineOutput::FillFooter(const commands::Category category,
-                              commands::CandidateWindow *candidate_window) {
+bool FillFooter(const commands::Category category,
+                commands::CandidateWindow *candidate_window) {
   if (category != commands::SUGGESTION && category != commands::PREDICTION &&
       category != commands::CONVERSION) {
     return false;
@@ -411,11 +400,8 @@ bool EngineOutput::FillFooter(const commands::Category category,
   return true;
 }
 
-// static
-bool EngineOutput::AddSegment(const absl::string_view key,
-                              const absl::string_view value,
-                              const uint32_t segment_type_mask,
-                              commands::Preedit *preedit) {
+bool AddSegment(const absl::string_view key, const absl::string_view value,
+                const uint32_t segment_type_mask, commands::Preedit *preedit) {
   // Key is always normalized as a preedit text.
   std::string normalized_key = TextNormalizer::NormalizeText(key);
 
@@ -446,9 +432,8 @@ bool EngineOutput::AddSegment(const absl::string_view key,
   return true;
 }
 
-// static
-void EngineOutput::FillPreedit(const composer::Composer &composer,
-                               commands::Preedit *preedit) {
+void FillPreedit(const composer::Composer &composer,
+                 commands::Preedit *preedit) {
   const std::string output = composer.GetStringForPreedit();
 
   constexpr uint32_t kBaseType = PREEDIT;
@@ -457,11 +442,8 @@ void EngineOutput::FillPreedit(const composer::Composer &composer,
   preedit->set_is_toggleable(composer.IsToggleable());
 }
 
-// static
-void EngineOutput::FillConversion(const Segments &segments,
-                                  const size_t segment_index,
-                                  const int candidate_id,
-                                  commands::Preedit *preedit) {
+void FillConversion(const Segments &segments, const size_t segment_index,
+                    const int candidate_id, commands::Preedit *preedit) {
   constexpr uint32_t kBaseType = CONVERSION;
   // Cursor position in conversion state should be the end of the preedit.
   size_t cursor = 0;
@@ -485,18 +467,16 @@ void EngineOutput::FillConversion(const Segments &segments,
   preedit->set_cursor(cursor);
 }
 
-// static
-void EngineOutput::FillConversionResultWithoutNormalization(
-    std::string key, std::string result, commands::Result *result_proto) {
+void FillConversionResultWithoutNormalization(std::string key,
+                                              std::string result,
+                                              commands::Result *result_proto) {
   result_proto->set_type(commands::Result::STRING);
   result_proto->set_key(std::move(key));
   result_proto->set_value(std::move(result));
 }
 
-// static
-void EngineOutput::FillConversionResult(const absl::string_view key,
-                                        std::string result,
-                                        commands::Result *result_proto) {
+void FillConversionResult(const absl::string_view key, std::string result,
+                          commands::Result *result_proto) {
   // Key should be normalized as a preedit text.
   std::string normalized_key = TextNormalizer::NormalizeText(key);
 
@@ -505,9 +485,8 @@ void EngineOutput::FillConversionResult(const absl::string_view key,
                                            std::move(result), result_proto);
 }
 
-// static
-void EngineOutput::FillPreeditResult(const absl::string_view preedit,
-                                     commands::Result *result_proto) {
+void FillPreeditResult(const absl::string_view preedit,
+                       commands::Result *result_proto) {
   std::string normalized_preedit = TextNormalizer::NormalizeText(preedit);
   // Copy before passing the value to FillConversionResultWithoutNormalization.
   // std::move() is evaluated out of order when used directly in the function
@@ -517,11 +496,11 @@ void EngineOutput::FillPreeditResult(const absl::string_view preedit,
       std::move(key), std::move(normalized_preedit), result_proto);
 }
 
-// static
-void EngineOutput::FillCursorOffsetResult(int32_t cursor_offset,
-                                          commands::Result *result_proto) {
+void FillCursorOffsetResult(int32_t cursor_offset,
+                            commands::Result *result_proto) {
   result_proto->set_cursor_offset(cursor_offset);
 }
 
+}  // namespace output
 }  // namespace engine
 }  // namespace mozc
diff --git a/src/engine/engine_output.h b/src/engine/engine_output.h
index bd85fcc5f..d2c16b8db 100644
--- a/src/engine/engine_output.h
+++ b/src/engine/engine_output.h
@@ -45,95 +45,90 @@
 
 namespace mozc {
 namespace engine {
+namespace output {
 
-class EngineOutput {
- public:
-  EngineOutput(const EngineOutput &) = delete;
-  EngineOutput &operator=(const EngineOutput &) = delete;
-
-  // Fill the CandidateWindow_Candidate protobuf with the contents of candidate.
-  static void FillCandidate(
-      const Segment &segment, const Candidate &candidate,
-      commands::CandidateWindow_Candidate *candidate_proto);
-
-  // Fill the CandidateWindow protobuf with the contents of candidate_list.
-  static void FillCandidateWindow(
-      const Segment &segment, const CandidateList &candidate_list,
-      size_t position, commands::CandidateWindow *candidate_window_proto);
-
-  // Fill the CandidateList protobuf with the contents of
-  // candidate_list.  Candidates in the candidate_list are flatten
-  // even if the candidate_list contains sub-candidate lists.
-  static void FillAllCandidateWords(
-      const Segment &segment, const CandidateList &candidate_list,
-      commands::Category category,
-      commands::CandidateList *candidate_list_proto);
-
-  // For debug. Fill the CandidateList protobuf with the
-  // removed_candidates_for_debug in the segment.
-  static void FillRemovedCandidates(
-      const Segment &segment, commands::CandidateList *candidate_list_proto);
-
-  // Check if the usages should be rendered on the current CandidateList status.
-  static bool ShouldShowUsages(const Segment &segment,
-                               const CandidateList &cand_list);
-
-  // Fill the usages of Candidates protobuf with the contents of candidate_list.
-  static void FillUsages(const Segment &segment, const CandidateList &cand_list,
+// Fill the CandidateWindow_Candidate protobuf with the contents of candidate.
+void FillCandidate(const Segment &segment, const Candidate &candidate,
+                   commands::CandidateWindow_Candidate *candidate_proto);
+
+// Fill the CandidateWindow protobuf with the contents of candidate_list.
+void FillCandidateWindow(const Segment &segment,
+                         const CandidateList &candidate_list, size_t position,
                          commands::CandidateWindow *candidate_window_proto);
 
-  // Fill the access key of Candidates protobuf with the sequence of shortcuts.
-  static void FillShortcuts(absl::string_view shortcuts,
-                            commands::CandidateWindow *candidate_window_proto);
+// Fill the CandidateList protobuf with the contents of
+// candidate_list.  Candidates in the candidate_list are flatten
+// even if the candidate_list contains sub-candidate lists.
+void FillAllCandidateWords(const Segment &segment,
+                           const CandidateList &candidate_list,
+                           commands::Category category,
+                           commands::CandidateList *candidate_list_proto);
+
+// For debug. Fill the CandidateList protobuf with the
+// removed_candidates_for_debug in the segment.
+void FillRemovedCandidates(const Segment &segment,
+                           commands::CandidateList *candidate_list_proto);
+
+// Check if the usages should be rendered on the current CandidateList status.
+bool ShouldShowUsages(const Segment &segment, const CandidateList &cand_list);
+
+// Fill the usages of Candidates protobuf with the contents of candidate_list.
+void FillUsages(const Segment &segment, const CandidateList &cand_list,
+                commands::CandidateWindow *candidate_window_proto);
+
+// Fill the access key of Candidates protobuf with the sequence of shortcuts.
+void FillShortcuts(absl::string_view shortcuts,
+                   commands::CandidateWindow *candidate_window_proto);
+
+// Fill the sub_label of footer_proto.  This function should be
+// called on dev_channel and unittest.
+void FillSubLabel(commands::Footer *footer_proto);
+
+// Fill the footer contents of Candidates protobuf.  If category is
+// modified, true is returned.  Otherwise false is returned.
+bool FillFooter(commands::Category category,
+                commands::CandidateWindow *candidate_window_proto);
+
+// Fill the Preedit protobuf with the contents of composer as a preedit.
+void FillPreedit(const composer::Composer &composer,
+                 commands::Preedit *preedit);
+
+// Fill the Preedit protobuf with the contents of segments as a conversion.
+void FillConversion(const Segments &segments, size_t segment_index,
+                    int candidate_id, commands::Preedit *preedit);
+
+enum SegmentType {
+  PREEDIT = 1,
+  CONVERSION = 2,
+  FOCUSED = 4,
+};
 
-  // Fill the sub_label of footer_proto.  This function should be
-  // called on dev_channel and unittest.
-  static void FillSubLabel(commands::Footer *footer_proto);
+// Add a Preedit::Segment protobuf to the Preedit protobuf with key
+// and value.  Return true iff. new segment is added to preedit.
+bool AddSegment(absl::string_view, absl::string_view value,
+                uint32_t segment_type_mask, commands::Preedit *preedit);
 
-  // Fill the footer contents of Candidates protobuf.  If category is
-  // modified, true is returned.  Otherwise false is returned.
-  static bool FillFooter(commands::Category category,
-                         commands::CandidateWindow *candidate_window_proto);
+// Fill the Result protobuf with the key and result strings
+// for a conversion result without any text normalization.
+void FillConversionResultWithoutNormalization(std::string key,
+                                              std::string result,
+                                              commands::Result *result_proto);
 
-  // Fill the Preedit protobuf with the contents of composer as a preedit.
-  static void FillPreedit(const composer::Composer &composer,
-                          commands::Preedit *preedit);
-
-  // Fill the Preedit protobuf with the contents of segments as a conversion.
-  static void FillConversion(const Segments &segments, size_t segment_index,
-                             int candidate_id, commands::Preedit *preedit);
-
-  enum SegmentType {
-    PREEDIT = 1,
-    CONVERSION = 2,
-    FOCUSED = 4,
-  };
-  // Add a Preedit::Segment protobuf to the Preedit protobuf with key
-  // and value.  Return true iff. new segment is added to preedit.
-  static bool AddSegment(absl::string_view, absl::string_view value,
-                         uint32_t segment_type_mask,
-                         commands::Preedit *preedit);
-
-  // Fill the Result protobuf with the key and result strings
-  // for a conversion result without any text normalization.
-  static void FillConversionResultWithoutNormalization(
-      std::string key, std::string result, commands::Result *result_proto);
-
-  // Fill the Result protobuf with the key and result strings
-  // normalizing the string for a conversion result.
-  static void FillConversionResult(absl::string_view key, std::string result,
-                                   commands::Result *result_proto);
-
-  // Fill the Result protobuf with the preedit string normalizing the
-  // string for a preedit result.
-  static void FillPreeditResult(absl::string_view preedit,
-                                commands::Result *result_proto);
-
-  // Fill the Result protobuf with cursor offset.
-  static void FillCursorOffsetResult(int32_t cursor_offset,
-                                     commands::Result *result_proto);
-};
+// Fill the Result protobuf with the key and result strings
+// normalizing the string for a conversion result.
+void FillConversionResult(absl::string_view key, std::string result,
+                          commands::Result *result_proto);
+
+// Fill the Result protobuf with the preedit string normalizing the
+// string for a preedit result.
+void FillPreeditResult(absl::string_view preedit,
+                       commands::Result *result_proto);
+
+// Fill the Result protobuf with cursor offset.
+void FillCursorOffsetResult(int32_t cursor_offset,
+                            commands::Result *result_proto);
 
+}  // namespace output
 }  // namespace engine
 }  // namespace mozc
 
diff --git a/src/engine/engine_output_test.cc b/src/engine/engine_output_test.cc
index 2a42d03e9..b6765736d 100644
--- a/src/engine/engine_output_test.cc
+++ b/src/engine/engine_output_test.cc
@@ -94,7 +94,7 @@ TEST(EngineOutputTest, FillCandidate) {
   candidate_list.AddCandidate(-789, "minus 789");
 
   candidate.set_id(13);
-  EngineOutput::FillCandidate(segment, candidate, &candidate_proto);
+  output::FillCandidate(segment, candidate, &candidate_proto);
   EXPECT_EQ(candidate_proto.id(), 13);
   EXPECT_EQ(candidate_proto.value(), kValue13);
   EXPECT_FALSE(candidate_proto.has_annotation());
@@ -102,7 +102,7 @@ TEST(EngineOutputTest, FillCandidate) {
   candidate.Clear();
   candidate_proto.Clear();
   candidate.set_id(42);
-  EngineOutput::FillCandidate(segment, candidate, &candidate_proto);
+  output::FillCandidate(segment, candidate, &candidate_proto);
   EXPECT_EQ(candidate_proto.id(), 42);
   EXPECT_EQ(candidate_proto.value(), kValue42);
   EXPECT_TRUE(candidate_proto.has_annotation());
@@ -113,7 +113,7 @@ TEST(EngineOutputTest, FillCandidate) {
   candidate.Clear();
   candidate_proto.Clear();
   candidate.set_subcandidate_list(&candidate_list);
-  EngineOutput::FillCandidate(segment, candidate, &candidate_proto);
+  output::FillCandidate(segment, candidate, &candidate_proto);
   EXPECT_TRUE(candidate_proto.has_id());
   EXPECT_EQ(candidate_proto.id(), kFirstIdInSubList);
   EXPECT_EQ(candidate_proto.value(), kSubcandidateList);
@@ -146,8 +146,8 @@ TEST(EngineOutputTest, FillCandidateWindow) {
   subcandidate_list.AddCandidate(4, "4");
 
   // Focused index = 0. page_size = 9.
-  EngineOutput::FillCandidateWindow(segment, candidate_list, 0,
-                                    &candidate_window_proto);
+  output::FillCandidateWindow(segment, candidate_list, 0,
+                              &candidate_window_proto);
   EXPECT_EQ(candidate_window_proto.page_size(), 9);
   EXPECT_EQ(candidate_window_proto.candidate_size(), 3);
   EXPECT_EQ(candidate_window_proto.position(), 0);
@@ -162,8 +162,8 @@ TEST(EngineOutputTest, FillCandidateWindow) {
   candidate_window_proto.Clear();
   candidate_list.MoveToId(3);
   candidate_list.set_page_size(5);
-  EngineOutput::FillCandidateWindow(segment, candidate_list, 1,
-                                    &candidate_window_proto);
+  output::FillCandidateWindow(segment, candidate_list, 1,
+                              &candidate_window_proto);
   EXPECT_EQ(candidate_window_proto.page_size(), 5);
   EXPECT_EQ(candidate_window_proto.candidate_size(), 3);
   EXPECT_EQ(candidate_window_proto.position(), 1);
@@ -194,8 +194,8 @@ TEST(EngineOutputTest, FillCandidateWindow) {
   candidate_window_proto.Clear();
   candidate_list.set_focused(false);
   subcandidate_list.set_focused(true);
-  EngineOutput::FillCandidateWindow(segment, candidate_list, 0,
-                                    &candidate_window_proto);
+  output::FillCandidateWindow(segment, candidate_list, 0,
+                              &candidate_window_proto);
   EXPECT_FALSE(candidate_window_proto.has_focused_index());
   EXPECT_TRUE(
       candidate_window_proto.sub_candidate_window().has_focused_index());
@@ -203,8 +203,8 @@ TEST(EngineOutputTest, FillCandidateWindow) {
   candidate_window_proto.Clear();
   candidate_list.set_focused(false);
   subcandidate_list.set_focused(false);
-  EngineOutput::FillCandidateWindow(segment, candidate_list, 0,
-                                    &candidate_window_proto);
+  output::FillCandidateWindow(segment, candidate_list, 0,
+                              &candidate_window_proto);
   EXPECT_FALSE(candidate_window_proto.has_focused_index());
   EXPECT_FALSE(
       candidate_window_proto.sub_candidate_window().has_focused_index());
@@ -212,8 +212,8 @@ TEST(EngineOutputTest, FillCandidateWindow) {
   candidate_window_proto.Clear();
   candidate_list.set_focused(true);
   subcandidate_list.set_focused(false);
-  EngineOutput::FillCandidateWindow(segment, candidate_list, 0,
-                                    &candidate_window_proto);
+  output::FillCandidateWindow(segment, candidate_list, 0,
+                              &candidate_window_proto);
   EXPECT_TRUE(candidate_window_proto.has_focused_index());
   EXPECT_FALSE(
       candidate_window_proto.sub_candidate_window().has_focused_index());
@@ -289,8 +289,8 @@ TEST(EngineOutputTest, FillAllCandidateWords) {
 
   // Execute FillAllCandidateWords
   const commands::Category kCategory = commands::PREDICTION;
-  EngineOutput::FillAllCandidateWords(segment, main_list, kCategory,
-                                      &candidates_proto);
+  output::FillAllCandidateWords(segment, main_list, kCategory,
+                                &candidates_proto);
 
   // Varidation
   EXPECT_EQ(candidates_proto.focused_index(), 1);
@@ -387,8 +387,8 @@ TEST(EngineOutputTest, FillAllCandidateWords_Attributes) {
 
   // Execute FillAllCandidateWords
   const commands::Category kCategory = commands::PREDICTION;
-  EngineOutput::FillAllCandidateWords(segment, candidate_list, kCategory,
-                                      &candidates_proto);
+  output::FillAllCandidateWords(segment, candidate_list, kCategory,
+                                &candidates_proto);
 
   // Varidation
   EXPECT_EQ(candidates_proto.focused_index(), 0);
@@ -427,7 +427,7 @@ TEST(EngineOutputTest, ShouldShowUsages) {
     candidate_list.AddSubCandidateList(&sub);
     candidate_list.set_focused(true);
     ASSERT_TRUE(candidate_list.MoveToId(0));
-    ASSERT_FALSE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_FALSE(output::ShouldShowUsages(segment, candidate_list));
   }
   {
     Segment segment;
@@ -441,7 +441,7 @@ TEST(EngineOutputTest, ShouldShowUsages) {
     candidate_list.AddSubCandidateList(&sub);
     candidate_list.set_focused(true);
     ASSERT_TRUE(candidate_list.MoveToId(0));
-    ASSERT_TRUE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_TRUE(output::ShouldShowUsages(segment, candidate_list));
   }
   {
     Segment segment;
@@ -470,19 +470,19 @@ TEST(EngineOutputTest, ShouldShowUsages) {
     //  [00-08],[09-17],[18-26],[27-29]+subcandidate
     candidate_list.set_focused(true);
     ASSERT_TRUE(candidate_list.MoveToId(0));
-    ASSERT_TRUE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_TRUE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(8));
-    ASSERT_TRUE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_TRUE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(9));
-    ASSERT_TRUE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_TRUE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(17));
-    ASSERT_TRUE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_TRUE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(18));
-    ASSERT_FALSE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_FALSE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(26));
-    ASSERT_FALSE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_FALSE(output::ShouldShowUsages(segment, candidate_list));
     ASSERT_TRUE(candidate_list.MoveToId(27));
-    ASSERT_FALSE(EngineOutput::ShouldShowUsages(segment, candidate_list));
+    ASSERT_FALSE(output::ShouldShowUsages(segment, candidate_list));
   }
 }
 
@@ -533,7 +533,7 @@ TEST(EngineOutputTest, FillUsages) {
 
   candidate_list.MoveToId(2);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   // There is no focused usage.
   EXPECT_FALSE(candidate_window_proto.usages().has_focused_index());
@@ -551,7 +551,7 @@ TEST(EngineOutputTest, FillUsages) {
 
   candidate_list.MoveToId(12);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   // Focused usage index is 20
   EXPECT_TRUE(candidate_window_proto.usages().has_focused_index());
@@ -580,7 +580,7 @@ TEST(EngineOutputTest, FillUsages) {
 
   candidate_list.MoveToId(19);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   EXPECT_TRUE(candidate_window_proto.usages().has_focused_index());
   EXPECT_EQ(candidate_window_proto.usages().focused_index(), 0);
@@ -599,7 +599,7 @@ TEST(EngineOutputTest, FillUsages) {
 
   candidate_list.MoveToId(20);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   EXPECT_TRUE(candidate_window_proto.usages().has_focused_index());
   EXPECT_EQ(candidate_window_proto.usages().focused_index(), 1);
@@ -607,7 +607,7 @@ TEST(EngineOutputTest, FillUsages) {
   // usages(id:100) of "val19" and "val21" are merged
   candidate_list.MoveToId(21);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   EXPECT_TRUE(candidate_window_proto.usages().has_focused_index());
   EXPECT_EQ(candidate_window_proto.usages().focused_index(), 0);
@@ -615,14 +615,14 @@ TEST(EngineOutputTest, FillUsages) {
   // usages(id:110) of "val20" and "val22" are merged
   candidate_list.MoveToId(22);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_TRUE(candidate_window_proto.has_usages());
   EXPECT_TRUE(candidate_window_proto.usages().has_focused_index());
   EXPECT_EQ(candidate_window_proto.usages().focused_index(), 1);
 
   candidate_list.MoveToId(28);
   candidate_window_proto.Clear();
-  EngineOutput::FillUsages(segment, candidate_list, &candidate_window_proto);
+  output::FillUsages(segment, candidate_list, &candidate_window_proto);
   ASSERT_FALSE(candidate_window_proto.has_usages());
 }
 
@@ -635,7 +635,7 @@ TEST(EngineOutputTest, FillShortcuts) {
   }
   ASSERT_EQ(candidate_window_proto1.candidate_size(), 10);
 
-  EngineOutput::FillShortcuts(kDigits, &candidate_window_proto1);
+  output::FillShortcuts(kDigits, &candidate_window_proto1);
   EXPECT_EQ(candidate_window_proto1.candidate(0).annotation().shortcut(),
             kDigits.substr(0, 1));
   EXPECT_EQ(candidate_window_proto1.candidate(8).annotation().shortcut(),
@@ -649,7 +649,7 @@ TEST(EngineOutputTest, FillShortcuts) {
   }
   ASSERT_EQ(candidate_window_proto2.candidate_size(), 3);
 
-  EngineOutput::FillShortcuts(kDigits, &candidate_window_proto2);
+  output::FillShortcuts(kDigits, &candidate_window_proto2);
   EXPECT_EQ(candidate_window_proto2.candidate(0).annotation().shortcut(),
             kDigits.substr(0, 1));
   EXPECT_EQ(candidate_window_proto2.candidate(2).annotation().shortcut(),
@@ -658,8 +658,7 @@ TEST(EngineOutputTest, FillShortcuts) {
 
 TEST(EngineOutputTest, FillFooter) {
   commands::CandidateWindow candidate_window;
-  EXPECT_TRUE(
-      EngineOutput::FillFooter(commands::SUGGESTION, &candidate_window));
+  EXPECT_TRUE(output::FillFooter(commands::SUGGESTION, &candidate_window));
   EXPECT_TRUE(candidate_window.has_footer());
 
 #if defined(CHANNEL_DEV) && defined(GOOGLE_JAPANESE_INPUT_BUILD)
@@ -677,16 +676,14 @@ TEST(EngineOutputTest, FillFooter) {
   EXPECT_FALSE(candidate_window.footer().logo_visible());
 
   candidate_window.Clear();
-  EXPECT_TRUE(
-      EngineOutput::FillFooter(commands::PREDICTION, &candidate_window));
+  EXPECT_TRUE(output::FillFooter(commands::PREDICTION, &candidate_window));
   EXPECT_TRUE(candidate_window.has_footer());
   EXPECT_FALSE(candidate_window.footer().has_label());
   EXPECT_TRUE(candidate_window.footer().index_visible());
   EXPECT_TRUE(candidate_window.footer().logo_visible());
 
   candidate_window.Clear();
-  EXPECT_TRUE(
-      EngineOutput::FillFooter(commands::CONVERSION, &candidate_window));
+  EXPECT_TRUE(output::FillFooter(commands::CONVERSION, &candidate_window));
   EXPECT_TRUE(candidate_window.has_footer());
   EXPECT_FALSE(candidate_window.footer().has_label());
   EXPECT_TRUE(candidate_window.footer().index_visible());
@@ -694,11 +691,11 @@ TEST(EngineOutputTest, FillFooter) {
 
   candidate_window.Clear();
   EXPECT_FALSE(
-      EngineOutput::FillFooter(commands::TRANSLITERATION, &candidate_window));
+      output::FillFooter(commands::TRANSLITERATION, &candidate_window));
   EXPECT_FALSE(candidate_window.has_footer());
 
   candidate_window.Clear();
-  EXPECT_FALSE(EngineOutput::FillFooter(commands::USAGE, &candidate_window));
+  EXPECT_FALSE(output::FillFooter(commands::USAGE, &candidate_window));
   EXPECT_FALSE(candidate_window.has_footer());
 
   candidate_window.Clear();
@@ -713,8 +710,7 @@ TEST(EngineOutputTest, FillFooter) {
   for (int i = 0; i < 20; ++i) {
     candidate_window.clear_footer();
     candidate_window.set_focused_index(i);
-    EXPECT_TRUE(
-        EngineOutput::FillFooter(commands::PREDICTION, &candidate_window));
+    EXPECT_TRUE(output::FillFooter(commands::PREDICTION, &candidate_window));
     if (i % 2 == 0) {
       ASSERT_TRUE(candidate_window.has_footer());
       ASSERT_TRUE(candidate_window.footer().has_label());
@@ -739,7 +735,7 @@ TEST(EngineOutputTest, FillFooter) {
 TEST(EngineOutputTest, FillSubLabel) {
   commands::Footer footer;
   footer.set_label("to be deleted");
-  EngineOutput::FillSubLabel(&footer);
+  output::FillSubLabel(&footer);
   EXPECT_TRUE(footer.has_sub_label());
   EXPECT_FALSE(footer.has_label());
   EXPECT_GT(footer.sub_label().size(), 6);  // 6 == strlen("build ")
@@ -754,8 +750,8 @@ TEST(EngineOutputTest, AddSegment) {
     // "〜" is a character to be processed by TextNormalizer::NormalizeText
     const std::string kKey = "ゔ〜 preedit focused";
     const std::string kValue = "ゔ〜 PREEDIT FOCUSED";
-    const int types = EngineOutput::PREEDIT | EngineOutput::FOCUSED;
-    EXPECT_TRUE(EngineOutput::AddSegment(kKey, kValue, types, &preedit));
+    const int types = output::PREEDIT | output::FOCUSED;
+    EXPECT_TRUE(output::AddSegment(kKey, kValue, types, &preedit));
     EXPECT_EQ(preedit.segment_size(), index + 1);
     const commands::Preedit::Segment &segment = preedit.segment(index);
 
@@ -771,8 +767,8 @@ TEST(EngineOutputTest, AddSegment) {
   {
     const std::string kKey = "ゔ〜 preedit";
     const std::string kValue = "ゔ〜 PREEDIT";
-    const int types = EngineOutput::PREEDIT;
-    EXPECT_TRUE(EngineOutput::AddSegment(kKey, kValue, types, &preedit));
+    const int types = output::PREEDIT;
+    EXPECT_TRUE(output::AddSegment(kKey, kValue, types, &preedit));
     EXPECT_EQ(preedit.segment_size(), index + 1);
     const commands::Preedit::Segment &segment = preedit.segment(index);
 
@@ -788,8 +784,8 @@ TEST(EngineOutputTest, AddSegment) {
   {
     const std::string kKey = "ゔ〜 conversion focused";
     const std::string kValue = "ゔ〜 CONVERSION FOCUSED";
-    const int types = EngineOutput::CONVERSION | EngineOutput::FOCUSED;
-    EXPECT_TRUE(EngineOutput::AddSegment(kKey, kValue, types, &preedit));
+    const int types = output::CONVERSION | output::FOCUSED;
+    EXPECT_TRUE(output::AddSegment(kKey, kValue, types, &preedit));
     EXPECT_EQ(preedit.segment_size(), index + 1);
     const commands::Preedit::Segment &segment = preedit.segment(index);
 
@@ -806,8 +802,8 @@ TEST(EngineOutputTest, AddSegment) {
   {
     const std::string kKey = "ゔ〜 conversion";
     const std::string kValue = "ゔ〜 CONVERSION";
-    const int types = EngineOutput::CONVERSION;
-    EXPECT_TRUE(EngineOutput::AddSegment(kKey, kValue, types, &preedit));
+    const int types = output::CONVERSION;
+    EXPECT_TRUE(output::AddSegment(kKey, kValue, types, &preedit));
     EXPECT_EQ(preedit.segment_size(), index + 1);
     const commands::Preedit::Segment &segment = preedit.segment(index);
 
@@ -824,8 +820,8 @@ TEST(EngineOutputTest, AddSegment) {
   {
     const std::string kKey = "abc";
     const std::string kValue = "";  // empty value
-    const int types = EngineOutput::CONVERSION;
-    EXPECT_FALSE(EngineOutput::AddSegment(kKey, kValue, types, &preedit));
+    const int types = output::CONVERSION;
+    EXPECT_FALSE(output::AddSegment(kKey, kValue, types, &preedit));
     EXPECT_EQ(preedit.segment_size(), index);
   }
 }
@@ -834,8 +830,7 @@ TEST(EngineOutputTest, FillConversionResultWithoutNormalization) {
   constexpr char kInput[] = "ゔ";
 
   commands::Result result;
-  EngineOutput::FillConversionResultWithoutNormalization(kInput, kInput,
-                                                         &result);
+  output::FillConversionResultWithoutNormalization(kInput, kInput, &result);
   EXPECT_EQ(result.type(), commands::Result::STRING);
   EXPECT_EQ(result.key(), kInput);    // should not be normalized
   EXPECT_EQ(result.value(), kInput);  // should not be normalized
@@ -843,7 +838,7 @@ TEST(EngineOutputTest, FillConversionResultWithoutNormalization) {
 
 TEST(EngineOutputTest, FillConversionResult) {
   commands::Result result;
-  EngineOutput::FillConversionResult("abc", "ABC", &result);
+  output::FillConversionResult("abc", "ABC", &result);
   EXPECT_EQ(result.type(), commands::Result::STRING);
   EXPECT_EQ(result.key(), "abc");
   EXPECT_EQ(result.value(), "ABC");
@@ -851,13 +846,13 @@ TEST(EngineOutputTest, FillConversionResult) {
 
 TEST(EngineOutputTest, FillCursorOffsetResult) {
   commands::Result result;
-  EngineOutput::FillCursorOffsetResult(-1, &result);
+  output::FillCursorOffsetResult(-1, &result);
   EXPECT_EQ(result.cursor_offset(), -1);
 }
 
 TEST(EngineOutputTest, FillPreeditResult) {
   commands::Result result;
-  EngineOutput::FillPreeditResult("ABC", &result);
+  output::FillPreeditResult("ABC", &result);
   EXPECT_EQ(result.type(), commands::Result::STRING);
   EXPECT_EQ(result.key(), "ABC");
   EXPECT_EQ(result.value(), "ABC");
@@ -883,8 +878,8 @@ TEST(EngineOutputTest, FillAllCandidateWords_NonFocused) {
   {
     // Execute FillAllCandidateWords
     const commands::Category kCategory = commands::SUGGESTION;
-    EngineOutput::FillAllCandidateWords(segment, main_list, kCategory,
-                                        &candidates_proto);
+    output::FillAllCandidateWords(segment, main_list, kCategory,
+                                  &candidates_proto);
 
     // Varidation
     EXPECT_FALSE(candidates_proto.has_focused_index());
@@ -895,8 +890,8 @@ TEST(EngineOutputTest, FillAllCandidateWords_NonFocused) {
     // When the category is SUGGESTION, has_focused_index never return true in
     // real usage. This is just a test case.
     const commands::Category kCategory = commands::SUGGESTION;
-    EngineOutput::FillAllCandidateWords(segment, main_list, kCategory,
-                                        &candidates_proto);
+    output::FillAllCandidateWords(segment, main_list, kCategory,
+                                  &candidates_proto);
 
     // Validation
     // If a candidate is focused, true is expected.
@@ -918,7 +913,7 @@ TEST(EngineOutputTest, FillRemovedCandidateWords) {
   segment.removed_candidates_for_debug_.push_back(candidate);
 
   // Execute FillAllCandidateWords
-  EngineOutput::FillRemovedCandidates(segment, &candidates_proto);
+  output::FillRemovedCandidates(segment, &candidates_proto);
 }
 
 }  // namespace engine
diff --git a/src/session/BUILD.bazel b/src/session/BUILD.bazel
index 45dad445b..c0bdd9faf 100644
--- a/src/session/BUILD.bazel
+++ b/src/session/BUILD.bazel
@@ -61,7 +61,6 @@ mozc_cc_library(
         "//composer:table",
         "//engine:engine_converter_interface",
         "//engine:engine_interface",
-        "//engine:engine_output",
         "//protocol:commands_cc_proto",
         "//protocol:config_cc_proto",
         "//testing:friend_test",
diff --git a/src/session/session.cc b/src/session/session.cc
index 0951025ef..8bfeaddcf 100644
--- a/src/session/session.cc
+++ b/src/session/session.cc
@@ -51,7 +51,6 @@
 #include "composer/table.h"
 #include "engine/engine_converter_interface.h"
 #include "engine/engine_interface.h"
-#include "engine/engine_output.h"
 #include "protocol/commands.pb.h"
 #include "protocol/config.pb.h"
 #include "session/ime_context.h"
@@ -2749,9 +2748,8 @@ void Session::OutputMode(commands::Command *command) const {
 
 void Session::OutputComposition(commands::Command *command) const {
   OutputMode(command);
-  commands::Preedit *preedit = command->mutable_output()->mutable_preedit();
-  // TODO(taku): Removes the dependency to SessionOutput.
-  engine::EngineOutput::FillPreedit(context_->composer(), preedit);
+  context_->converter().FillPreedit(
+      context_->composer(), command->mutable_output()->mutable_preedit());
 }
 
 void Session::OutputKey(commands::Command *command) const {