Add step 626 AST mutation preview model

editor/CMakeLists.txt

@@ -4513,4 +4513,13 @@ target_link_libraries(step625_test PRIVATE
     tree_sitter_javascript tree_sitter_typescript
     tree_sitter_java tree_sitter_rust tree_sitter_go)
 
+add_executable(step626_test tests/step626_test.cpp)
+target_include_directories(step626_test PRIVATE src)
+target_link_libraries(step626_test PRIVATE
+    nlohmann_json::nlohmann_json
+    unofficial::tree-sitter::tree-sitter
+    tree_sitter_python tree_sitter_cpp tree_sitter_elisp
+    tree_sitter_javascript tree_sitter_typescript
+    tree_sitter_java tree_sitter_rust tree_sitter_go)
+
 # Step 12: Dear ImGui shell scaffolding created (main.cpp exists but not built due to dependencies)

editor/src/AgentChatPanelModel.h

@@ -2,6 +2,7 @@
 // Step 624: Agent Chat Panel model
 
 #include "AgentToolCallVisualization.h"
+#include "AgentMutationPreview.h"
 
 #include <cctype>
 #include <string>
@@ -22,6 +23,7 @@ struct AgentChatMessage {
 struct AgentChatState {
     std::vector<AgentChatMessage> messages;
     std::vector<AgentToolCallView> toolCalls;
+    std::vector<AgentMutationPreview> mutationPreviews;
     std::string draftInput;
     bool autoScroll = true;
     bool open = false;
@@ -69,6 +71,22 @@ public:
         state->autoScroll = true;
     }
 
+    static void addMutationPreview(AgentChatState* state,
+                                   const std::string& previewId,
+                                   const std::string& mutationJson,
+                                   const std::string& beforeCode,
+                                   const std::string& afterCode,
+                                   const std::string& timestamp) {
+        if (!state) return;
+        AgentMutationPreview preview = AgentMutationPreviewBuilder::build(
+            previewId, mutationJson, beforeCode, afterCode);
+        state->mutationPreviews.push_back(preview);
+        std::string label = std::string("[PREVIEW] ") + previewId +
+                            (preview.hasChanges ? " (changes)" : " (no changes)");
+        state->messages.push_back({AgentChatRole::Tool, label, timestamp});
+        state->autoScroll = true;
+    }
+
     static const char* roleLabel(AgentChatRole role) {
         if (role == AgentChatRole::User) return "user";
         if (role == AgentChatRole::Assistant) return "assistant";

editor/src/AgentMutationPreview.h

@@ -0,0 +1,41 @@
+#pragma once
+// Step 626: AST mutation preview model
+
+#include "DiffUtils.h"
+
+#include <string>
+#include <vector>
+
+struct AgentMutationPreview {
+    std::string previewId;
+    std::string mutationJson;
+    std::string beforeCode;
+    std::string afterCode;
+    LineDiff diff;
+    bool hasChanges = false;
+};
+
+class AgentMutationPreviewBuilder {
+public:
+    static AgentMutationPreview build(const std::string& previewId,
+                                      const std::string& mutationJson,
+                                      const std::string& beforeCode,
+                                      const std::string& afterCode) {
+        AgentMutationPreview out;
+        out.previewId = previewId;
+        out.mutationJson = mutationJson;
+        out.beforeCode = beforeCode;
+        out.afterCode = afterCode;
+        out.diff = buildLineDiff(beforeCode, afterCode);
+        out.hasChanges = !out.diff.beforeLines.empty() || !out.diff.afterLines.empty();
+        return out;
+    }
+
+    static std::vector<std::string> beforeLines(const AgentMutationPreview& preview) {
+        return splitLines(preview.beforeCode);
+    }
+
+    static std::vector<std::string> afterLines(const AgentMutationPreview& preview) {
+        return splitLines(preview.afterCode);
+    }
+};

editor/src/panels/AgentChatPanel.h

@@ -47,6 +47,33 @@ static void renderAgentChatPanel(EditorState& state) {
         }
     }
 
+    if (!chat.mutationPreviews.empty()) {
+        ImGui::Separator();
+        ImGui::TextUnformatted("Mutation Previews");
+        for (std::size_t i = 0; i < chat.mutationPreviews.size(); ++i) {
+            const auto& preview = chat.mutationPreviews[i];
+            std::string header = preview.previewId + (preview.hasChanges ? " (changes)" : " (no changes)");
+            if (ImGui::CollapsingHeader((header + "##preview_" + std::to_string(i)).c_str())) {
+                ImGui::TextUnformatted("Mutation JSON");
+                ImGui::BeginChild(("##preview_json_" + std::to_string(i)).c_str(), ImVec2(-1, 60), true);
+                ImGui::TextUnformatted(preview.mutationJson.c_str());
+                ImGui::EndChild();
+
+                ImGui::Columns(2, ("##preview_cols_" + std::to_string(i)).c_str(), true);
+                ImGui::TextUnformatted("Before");
+                ImGui::BeginChild(("##preview_before_" + std::to_string(i)).c_str(), ImVec2(0, 100), true);
+                ImGui::TextUnformatted(preview.beforeCode.c_str());
+                ImGui::EndChild();
+                ImGui::NextColumn();
+                ImGui::TextUnformatted("After");
+                ImGui::BeginChild(("##preview_after_" + std::to_string(i)).c_str(), ImVec2(0, 100), true);
+                ImGui::TextUnformatted(preview.afterCode.c_str());
+                ImGui::EndChild();
+                ImGui::Columns(1);
+            }
+        }
+    }
+
     ImGuiInputTextFlags flags = ImGuiInputTextFlags_AllowTabInput;
     InputTextMultilineStr("##AgentChatInput", &chat.draftInput, ImVec2(-90, 80), flags);
     ImGui::SameLine();

editor/tests/step626_test.cpp

@@ -0,0 +1,135 @@
+// Step 626: AST mutation preview (12 tests)
+
+#include "AgentChatPanelModel.h"
+#include "AgentMutationPreview.h"
+
+#include <iostream>
+
+static int passed = 0, failed = 0;
+#define TEST(name) { std::cout << "  " << #name << "... "; }
+#define PASS() { std::cout << "PASS\n"; ++passed; }
+#define FAIL(msg) { std::cout << "FAIL: " << msg << "\n"; ++failed; }
+#define CHECK(cond, msg) if (!(cond)) { FAIL(msg); return; } else {}
+
+static std::string beforeCode() {
+    return "def add(a, b):\n    return a + b\n";
+}
+
+static std::string afterCode() {
+    return "def add_numbers(a, b):\n    return a + b\n";
+}
+
+void test_build_sets_preview_id() {
+    TEST(build_sets_preview_id);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    CHECK(preview.previewId == "p1", "previewId mismatch");
+    PASS();
+}
+
+void test_build_carries_mutation_json() {
+    TEST(build_carries_mutation_json);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{\"type\":\"setProperty\"}", beforeCode(), afterCode());
+    CHECK(preview.mutationJson.find("setProperty") != std::string::npos, "mutation json mismatch");
+    PASS();
+}
+
+void test_build_sets_before_and_after_code() {
+    TEST(build_sets_before_and_after_code);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    CHECK(preview.beforeCode == beforeCode(), "before code mismatch");
+    CHECK(preview.afterCode == afterCode(), "after code mismatch");
+    PASS();
+}
+
+void test_build_detects_changed_lines() {
+    TEST(build_detects_changed_lines);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    CHECK(!preview.diff.beforeLines.empty(), "before diff should not be empty");
+    CHECK(!preview.diff.afterLines.empty(), "after diff should not be empty");
+    PASS();
+}
+
+void test_build_marks_has_changes_true_when_diff_exists() {
+    TEST(build_marks_has_changes_true_when_diff_exists);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    CHECK(preview.hasChanges, "hasChanges should be true");
+    PASS();
+}
+
+void test_build_marks_has_changes_false_when_equal() {
+    TEST(build_marks_has_changes_false_when_equal);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), beforeCode());
+    CHECK(!preview.hasChanges, "hasChanges should be false");
+    PASS();
+}
+
+void test_before_lines_split_preserves_count() {
+    TEST(before_lines_split_preserves_count);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    auto lines = AgentMutationPreviewBuilder::beforeLines(preview);
+    CHECK(lines.size() >= 2, "expected at least 2 lines");
+    PASS();
+}
+
+void test_after_lines_split_preserves_count() {
+    TEST(after_lines_split_preserves_count);
+    auto preview = AgentMutationPreviewBuilder::build("p1", "{}", beforeCode(), afterCode());
+    auto lines = AgentMutationPreviewBuilder::afterLines(preview);
+    CHECK(lines.size() >= 2, "expected at least 2 lines");
+    PASS();
+}
+
+void test_chat_add_mutation_preview_appends_record() {
+    TEST(chat_add_mutation_preview_appends_record);
+    AgentChatState state;
+    AgentChatPanelModel::addMutationPreview(&state, "preview-1", "{\"type\":\"setProperty\"}",
+                                            beforeCode(), afterCode(), "11:10");
+    CHECK(state.mutationPreviews.size() == 1, "preview count mismatch");
+    CHECK(state.mutationPreviews[0].previewId == "preview-1", "preview id mismatch");
+    PASS();
+}
+
+void test_chat_add_mutation_preview_appends_message() {
+    TEST(chat_add_mutation_preview_appends_message);
+    AgentChatState state;
+    AgentChatPanelModel::addMutationPreview(&state, "preview-1", "{}", beforeCode(), afterCode(), "11:11");
+    CHECK(state.messages.size() == 1, "message count mismatch");
+    CHECK(state.messages[0].content.find("[PREVIEW] preview-1") != std::string::npos, "preview message missing");
+    PASS();
+}
+
+void test_chat_preview_message_marks_change_state() {
+    TEST(chat_preview_message_marks_change_state);
+    AgentChatState state;
+    AgentChatPanelModel::addMutationPreview(&state, "preview-1", "{}", beforeCode(), afterCode(), "11:12");
+    CHECK(state.messages[0].content.find("(changes)") != std::string::npos, "expected changes marker");
+    PASS();
+}
+
+void test_chat_preview_message_marks_no_change_state() {
+    TEST(chat_preview_message_marks_no_change_state);
+    AgentChatState state;
+    AgentChatPanelModel::addMutationPreview(&state, "preview-2", "{}", beforeCode(), beforeCode(), "11:13");
+    CHECK(state.messages[0].content.find("(no changes)") != std::string::npos, "expected no-changes marker");
+    PASS();
+}
+
+int main() {
+    std::cout << "Step 626: AST mutation preview\n";
+
+    test_build_sets_preview_id();                            // 1
+    test_build_carries_mutation_json();                      // 2
+    test_build_sets_before_and_after_code();                 // 3
+    test_build_detects_changed_lines();                      // 4
+    test_build_marks_has_changes_true_when_diff_exists();    // 5
+    test_build_marks_has_changes_false_when_equal();         // 6
+    test_before_lines_split_preserves_count();               // 7
+    test_after_lines_split_preserves_count();                // 8
+    test_chat_add_mutation_preview_appends_record();         // 9
+    test_chat_add_mutation_preview_appends_message();        // 10
+    test_chat_preview_message_marks_change_state();          // 11
+    test_chat_preview_message_marks_no_change_state();       // 12
+
+    std::cout << "\nResults: " << passed << "/" << (passed + failed) << " passed\n";
+    return failed == 0 ? 0 : 1;
+}

progress.md

@@ -12493,3 +12493,37 @@ JSON payload capture.
 - `editor/src/panels/AgentChatPanel.h` (`58` <= `600`)
 - `editor/tests/step625_test.cpp` within test-file size guidance (`155` lines)
 - Header-only architecture and naming conventions remain aligned with `ARCHITECTURE.md`
+
+### Step 626: AST mutation preview
+**Status:** PASS (12/12 tests)
+
+Adds mutation preview records with before/after code snapshots and line-level
+diff metadata so pending agent edits can be inspected before application.
+
+**Files added:**
+- `editor/src/AgentMutationPreview.h` - preview model:
+  - before/after code capture
+  - line-diff generation via `DiffUtils`
+  - change-detection flagging and split-line helpers
+- `editor/tests/step626_test.cpp` - 12 tests covering:
+  - preview creation and payload retention
+  - diff/change detection behavior
+  - chat integration for preview record + message insertion
+
+**Files modified:**
+- `editor/src/AgentChatPanelModel.h` - added mutation preview storage + append helper
+- `editor/src/panels/AgentChatPanel.h` - added collapsible side-by-side preview rendering
+- `editor/CMakeLists.txt` - `step626_test` target
+
+**Verification run:**
+- `cmake -S editor -B editor/build-native` - PASS
+- `cmake --build editor/build-native --target step626_test step625_test` - PASS
+- `./editor/build-native/step626_test` - PASS (12/12)
+- `./editor/build-native/step625_test` - PASS (12/12) regression coverage
+
+**Architecture gate check:**
+- `editor/src/AgentMutationPreview.h` (`41` <= `600`)
+- `editor/src/AgentChatPanelModel.h` (`109` <= `600`)
+- `editor/src/panels/AgentChatPanel.h` (`85` <= `600`)
+- `editor/tests/step626_test.cpp` within test-file size guidance (`135` lines)
+- Header-only architecture and naming conventions remain aligned with `ARCHITECTURE.md`