Phase 3d complete: editor infrastructure (Steps 55-58)

Step 55: WelcomeScreen (actions, recent files, tips, visibility) - 7/7 tests
Step 56: ElispCommandBuilder + MockEmacsConnection (escaping, daemon lifecycle) - 6/6 tests
Step 57: BufferManager (multi-file open/close/switch, language/modified tracking) - 7/7 tests
Step 58: EditorMode (per-language indent, comment toggle, bracket pairs, snippets) - 8/8 tests

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

editor/src/BufferManager.h

@@ -0,0 +1,108 @@
+#pragma once
+// Step 57: Buffer management
+//
+// BufferManager tracks multiple open file buffers. Each buffer has a path,
+// content, language, and modified flag. One buffer is active at a time.
+// Provides open, close, switch, and content access operations.
+
+#include <string>
+#include <vector>
+#include <map>
+
+class BufferManager {
+public:
+    struct BufferInfo {
+        std::string path;
+        std::string content;
+        std::string language;
+        bool modified = false;
+    };
+
+    BufferManager() = default;
+
+    // Open a file into a buffer (makes it active)
+    bool openBuffer(const std::string& path, const std::string& content,
+                    const std::string& language) {
+        if (hasBuffer(path)) return false;  // already open
+        BufferInfo info{path, content, language, false};
+        buffers_[path] = info;
+        activeBuffer_ = path;
+        return true;
+    }
+
+    // Close a buffer by path
+    bool closeBuffer(const std::string& path) {
+        auto it = buffers_.find(path);
+        if (it == buffers_.end()) return false;
+        buffers_.erase(it);
+        // If we closed the active buffer, switch to another
+        if (activeBuffer_ == path) {
+            if (!buffers_.empty())
+                activeBuffer_ = buffers_.begin()->first;
+            else
+                activeBuffer_.clear();
+        }
+        return true;
+    }
+
+    // Get current active buffer path
+    std::string getActiveBufferPath() const { return activeBuffer_; }
+
+    // Switch to a different buffer
+    bool switchToBuffer(const std::string& path) {
+        if (!hasBuffer(path)) return false;
+        activeBuffer_ = path;
+        return true;
+    }
+
+    // Get buffer content
+    std::string getBufferContent(const std::string& path) const {
+        auto it = buffers_.find(path);
+        if (it == buffers_.end()) return "";
+        return it->second.content;
+    }
+
+    // Set buffer content
+    void setBufferContent(const std::string& path, const std::string& content) {
+        auto it = buffers_.find(path);
+        if (it != buffers_.end()) {
+            it->second.content = content;
+        }
+    }
+
+    // Get list of all open buffer paths
+    std::vector<std::string> getOpenBuffers() const {
+        std::vector<std::string> result;
+        for (const auto& [path, _] : buffers_) {
+            result.push_back(path);
+        }
+        return result;
+    }
+
+    // Check if a buffer exists
+    bool hasBuffer(const std::string& path) const {
+        return buffers_.find(path) != buffers_.end();
+    }
+
+    // Get buffer info
+    BufferInfo getBufferInfo(const std::string& path) const {
+        auto it = buffers_.find(path);
+        if (it != buffers_.end()) return it->second;
+        return {};
+    }
+
+    // Mark buffer as modified
+    void setModified(const std::string& path, bool modified) {
+        auto it = buffers_.find(path);
+        if (it != buffers_.end()) {
+            it->second.modified = modified;
+        }
+    }
+
+    // Get number of open buffers
+    size_t bufferCount() const { return buffers_.size(); }
+
+private:
+    std::map<std::string, BufferInfo> buffers_;
+    std::string activeBuffer_;
+};