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/WelcomeScreen.h

@@ -0,0 +1,111 @@
+#pragma once
+// Step 55: Welcome screen component
+//
+// WelcomeScreen provides a VSCode-style welcome tab for the editor.
+// Shows recent files, quick actions, keybinding profile info, and tips.
+// Rendered as an ImGui panel or tab content.
+
+#include <string>
+#include <vector>
+#include <functional>
+
+struct WelcomeAction {
+    std::string label;
+    std::string description;
+    std::string shortcut;  // e.g. "Ctrl+N"
+};
+
+struct RecentFile {
+    std::string path;
+    std::string language;
+    std::string displayName;  // just the filename
+};
+
+class WelcomeScreen {
+public:
+    WelcomeScreen() {
+        // Default quick actions
+        actions_ = {
+            {"New File",        "Create a new empty file",               "Ctrl+N"},
+            {"Open File",       "Open an existing file",                 "Ctrl+O"},
+            {"Change Language", "Switch the active language mode",       ""},
+            {"Keybindings",     "Choose VSCode, JetBrains, or Emacs keys", ""},
+        };
+
+        tips_ = {
+            "Use the Language menu to switch between Python, C++, and Elisp.",
+            "The AST tab shows your code's abstract syntax tree in real time.",
+            "The Generated tab shows target-language output from the AST.",
+            "Switch keybinding profiles from the Keybindings menu.",
+            "Whetstone annotations (@Reclaim, @Owner, @Lifetime) express memory intent.",
+            "The Highlighted tab shows syntax coloring via tree-sitter.",
+        };
+    }
+
+    // --- Data access ---
+
+    const std::string& getTitle() const { return title_; }
+    void setTitle(const std::string& t) { title_ = t; }
+
+    const std::string& getSubtitle() const { return subtitle_; }
+    void setSubtitle(const std::string& s) { subtitle_ = s; }
+
+    const std::vector<WelcomeAction>& getActions() const { return actions_; }
+    void setActions(const std::vector<WelcomeAction>& a) { actions_ = a; }
+
+    const std::vector<RecentFile>& getRecentFiles() const { return recentFiles_; }
+    void addRecentFile(const std::string& path, const std::string& lang) {
+        // Extract display name from path
+        std::string name = path;
+        auto sep = path.find_last_of("/\\");
+        if (sep != std::string::npos) name = path.substr(sep + 1);
+        // Don't add duplicates
+        for (const auto& f : recentFiles_) {
+            if (f.path == path) return;
+        }
+        // Keep max 10 recent files
+        if (recentFiles_.size() >= 10) recentFiles_.pop_back();
+        recentFiles_.insert(recentFiles_.begin(), {path, lang, name});
+    }
+
+    void clearRecentFiles() { recentFiles_.clear(); }
+
+    const std::vector<std::string>& getTips() const { return tips_; }
+
+    // Get the next tip (cycles through)
+    std::string getNextTip() {
+        if (tips_.empty()) return "";
+        std::string tip = tips_[tipIndex_ % tips_.size()];
+        ++tipIndex_;
+        return tip;
+    }
+
+    // Get a specific tip by index
+    std::string getTip(size_t index) const {
+        if (index >= tips_.size()) return "";
+        return tips_[index];
+    }
+
+    // --- Visibility ---
+
+    bool isVisible() const { return visible_; }
+    void setVisible(bool v) { visible_ = v; }
+    void show() { visible_ = true; }
+    void hide() { visible_ = false; }
+
+    // --- Version info ---
+
+    const std::string& getVersion() const { return version_; }
+    void setVersion(const std::string& v) { version_ = v; }
+
+private:
+    std::string title_    = "Whetstone Editor";
+    std::string subtitle_ = "Semantic Annotation DSL for Cross-Language Code Generation";
+    std::string version_  = "0.3.0";
+    bool visible_         = true;
+
+    std::vector<WelcomeAction> actions_;
+    std::vector<RecentFile>    recentFiles_;
+    std::vector<std::string>   tips_;
+    size_t tipIndex_ = 0;
+};